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Title: The Glaciers of the Alps
Being a narrative of excursions and ascents, etc.
Author: John Tyndall
Release Date: November 2, 2010 [EBook #34192]
Language: English
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[Illustration: THE MER DE GLACE
Showing the Cleft Station at Trélaporte, les Echelets, the Tacul, the
Périades and the Grande Jorasse.]
THE
GLACIERS OF THE ALPS.
BEING
A NARRATIVE OF EXCURSIONS AND ASCENTS,
AN ACCOUNT OF THE ORIGIN AND PHENOMENA OF GLACIERS,
AND
AN EXPOSITION OF THE PHYSICAL PRINCIPLES
TO WHICH THEY ARE RELATED.
BY JOHN TYNDALL, F.R.S.
WITH ILLUSTRATIONS.
_NEW EDITION._
LONGMANS, GREEN, AND CO.
LONDON, NEW YORK, AND BOMBAY.
1896.
_All rights reserved_
TO
MICHAEL FARADAY,
THIS BOOK
IS AFFECTIONATELY INSCRIBED.
1860.
PREFACE.
In the following work I have not attempted to mix Narrative and Science,
believing that the mind once interested in the one, cannot with
satisfaction pass abruptly to the other. The book is therefore divided
into Two Parts: the first chiefly narrative, and the second chiefly
scientific.
In Part I. I have sought to convey some notion of the life of an Alpine
explorer, and of the means by which his knowledge is acquired. In Part
II. an attempt is made to classify such knowledge, and to refer the
observed phenomena to their physical causes.
The Second Part of the work is written with a desire to interest
intelligent persons who may not possess any special scientific culture.
For their sakes I have dwelt more fully on principles than I should have
done in presence of a purely scientific audience. The brief sketch of
the nature of Light and Heat, with which Part II. is commenced, will
not, I trust, prove uninteresting to the reader for whom it is more
especially designed.
Should any obscurity exist as to the meaning of the terms Structure,
Dirt-bands, Regelation, Interference, and others, which occur in Part
I., it will entirely disappear in the perusal of Part II.
Two ascents of Mont Blanc and two of Monte Rosa are recorded; but the
aspects of nature, and other circumstances which attracted my attention,
were so different in the respective cases, that repetition was scarcely
possible.
The numerous interesting articles on glaciers which have been published
during the last eighteen months, and the various lively discussions to
which the subject has given birth, have induced me to make myself better
acquainted than I had previously been with the historic aspect of the
question. In some important cases I have stated, with the utmost
possible brevity, the results of my reading, and thus, I trust,
contributed to the formation of a just estimate of men whose labours in
this field were long anterior to my own.
J. T.
_Royal Institution, June, 1860._
PREFATORY NOTE.
"Glaciers of the Alps" was published nearly six and thirty years ago,
and has been long out of print, its teaching in a condensed form having
been embodied in the little book called "Forms of Water." The two books
are, however, distinct in character; each appears to me to supplement
the other; and as the older work is still frequently asked for, I have,
at the suggestion of my husband's Publishers, consented to the present
reprint, which may be followed later on by a reprint of "Hours of
Exercise."
Before reproducing a book written so long ago, I sought to assure myself
that it contained nothing touching the views of others which my husband
might have wished at the present time to alter or omit. With this object
I asked Lord Kelvin to be good enough to read over for me the pages
which deal with the history of the subject and with discussions in which
he himself took an active part. In kind response he writes:--"... After
carefully going through all the passages relating to those old
differences I could not advise the omission of any of them from the
reprint. There were, no doubt, some keen differences of opinion and
judgement among us, and other friends now gone from us, but I think the
statements on controversial points in this beautiful and interesting
book of your husband's are all thoroughly courteous and considerate of
feelings, and have been felt to be so by those whose views were
contested or criticised in them."
The current spelling of Swiss names has changed considerably since
"Glaciers of the Alps" was written, but, except in the very few cases
where an obvious oversight called for correction, the text has been left
unaltered. Only the Index has been made somewhat fuller than it was.
L. C. T.
_January, 1896._
CONTENTS.
PART I.
Page
1.--Introductory. 1
Visit to Penrhyn; the Cleavage of Slate Rocks; Sedgwick's
theory--its difficulties; Sharpe's observations; Sorby's
experiments; Lecture at the Royal Institution; Glacier
Lamination; arrangement of an expedition to Switzerland
2.--Expedition of 1856: the Oberland. 9
Valley of Lauterbrunnen; Pliability of rocks; the Wengern
Alp; the Jungfrau and Silberhorn; Ice avalanches; Glaciers
formed from them; Scene from the Little Scheideck; the Lower
Grindelwald Glacier; the Heisse Platte--its Avalanches; Ice
Minarets and Blocks; Echoes of the Wetterhorn; analogy with
the Reflection of Light from angular mirrors; the
Reichenbach Cascade; Handeck Fall; the Grimsel; the Unteraar
Glacier; hut of M. Dollfuss; Hôtel des Neufchâtelois; the
Rhone glacier from the Mayenwand; expedition up the glacier;
Coloured Rings round the sun; crevasses of the _névé_;
extraordinary meteorological phenomenon; Spirit of the
Brocken
3.--The Tyrol. 23
Kaunserthal and the Gebatsch Alp; Senner or Cheesemakers;
Gebatsch Glacier; a night in a cowshed; passage to
Lantaufer; a chamois on the rocks; my Guide; the atmospheric
snow-line; passage of the Stelvio; Colour of fresh snow;
Bormio; the pass recrossed by night; aspect of the
mountains; Meran to Unserfrau; passage of the Hochjoch to
Fend; singular hailstorm; wild glacier region; hidden
crevasses; First Paper presented to the Royal Society
4.--Expedition of 1857: the Lake of Geneva. 33
Blueness of the water; the head of the Lake; appearance of
the Rhone; subsidence of particles; Mirage
5.--Chamouni and the Montanvert. 37
Arrival; Coloured Shadows on the snow; Source of the
Arveiron; fall of the Vault; "Sunrise in the Valley of
Chamouni;" Scratched Rocks; quarters at the Montanvert
6.--The Mer de Glace. 42
Not a _Sea_ but a _River_ of ice; Wave-forms on its surface;
their explanation; Structure and Strata; Glacier Tables;
first view of the Dirt Bands; influence of Illumination in
rendering them visible; the Eye incapable of detecting
differences between intense lights
7. 46
Measurements commenced; the "Cleft Station" at Trélaporte;
Regelation of snow granules; two chamois; view of the Mer de
Glace and its Tributaries; _Séracs_ of the Col du Géant;
Sliding and Viscous theories; Rending of the ice; Striæ on
its surface; White Ice-seams
8. 57
Alone upon the glacier; Lakes and Rivulets; parallel between
Glacier and Geological disturbance; splendid rainbow; aspect
of the glacier at the base of the Séracs; visit to the Chief
Guide at Chamouni; Liberties granted
9.--The Jardin. 61
Glacier du Talèfre; Jardin divides the névé; Blue Veins near
the summit; surrounding scene; Moraines and Avalanches;
Cascade du Talèfre; dangers on approaching it from above
10. 64
Lightning and Rain; Spherical hailstones; an evening among
the crevasses; Dangerous Leap; ice-practice; preparations
for an ascent of Mont Blanc
11.--First Ascent of Mont Blanc (1857). 68
Across the mountain to the Glacier des Bossons; its
crevasses; Ladder left behind; consequent difficulties; the
Grands Mulets; Twinkling and change of Colour of the Stars;
moonlight on the mountains; start with one guide;
difficulties among the crevasses; the Petit Plateau; Séracs
of the Dôme du Goûter; bad condition of snow; the Grand
Plateau; Coloured Spectra round the sun; the lost Guides;
the Route missed; dangerous ice-slope; Guide exhausted;
cutting steps; cheerless prospect; the Corridor; the Mur de
la Côte; the Petits Mulets; food and drink disappear;
Physiological experiences on the Calotte; Summit attained;
the Clouds and Mountains; experiment on Sound; colour of the
snow; the descent; a solitary prisoner; second night at the
Grands Mulets; Inflammation of eyes; a blind man among the
crevasses; descent to Chamouni; thunder on Mont Blanc
12. 86
Life at the Montanvert; glacier "Blower;" Cascade of the
Talèfre; difficulties in setting out lines; departure from
the Montanvert; my hosts; prospect from the Glacier des
Bois; Edouard Simond
13.--Expedition of 1858. 92
Origin and aim of the expedition; Laminated Structure of the
ice
14.--Passage of the Strahleck. 93
Unpromising weather; appearance of the glacier and of the
adjacent mountains; Transverse Protuberances; Dirt Bands;
Structure; a Slip on a snow slope; the Finsteraarhorn; the
Schreckhorn; extraordinary Atmospheric Effects; Summit of
the Strahleck; Grand Amphitheatre; mutations of the clouds;
descent of the rocks; a Bergschrund; fog in the valley;
descent to the Grimsel
15. 99
Ancient Glaciers in the valley of Hasli; Rounded, Polished,
and Striated Rocks; level of the ancient ice; Groovings on
the Grimsel Pass; glacier of the Rhone; descent of the Rhone
valley; the Æggischhorn; Cloud Iridescences; the Aletsch
glacier; the Märjelen See; Icebergs; Tributaries of the
Aletsch; Grand glacier-region; crevasses; a chamois deceived
16.--Ascent of the Finsteraarhorn. 104
Character of my Guide; iridescent cloud; evening on the
Faulberg; the Jungfrau and her neighbours; a Mountain Cave;
the Jungfrau before dawn; contemplated visit; the Grünhorn
Lücke; Magnificent Corridor; sunrise; névé of the Viesch
glacier; halt at the base of the Finsteraarhorn; Spurs and
Couloirs of the mountain; Pyramidal Crest; scene of
Agassiz's observations; a hard climb; discipline of such an
ascent; Boiling Point; Registering Thermometer, its fate;
daring utterance; descent by glissades; the Viesch glacier;
hidden crevasses; a brave and competent guide
17. 119
Subsequent days at the Æggischhorn; Afloat on the Icebergs;
Bedding and Structure; Ancient Moraines of the Aletsch;
Scratched Rocks; passage of the mountains to the end of the
glacier; a wild gorge; arrival at Zermatt; the Riffelberg
18.--First Ascent of Monte Rosa. 122
The ascent new to myself and my guide; directions; Ulrich
Lauener; Ominous Clouds; passage of the Görner Glacier;
Roches Moutonnées; Avalanche from the Twins; gradual advance
of clouds; bridged chasms; Scene from a cliff; apparent
atmospheric struggle; Sound of the snow; Dangerous Edge;
Overhanging Cornice; staff driven through it; increased
obscurity; Rocky Crest; loss of pocket-book; Summit
attained; Boiling Point; fall of snow; exquisite forms of
the Snow Crystals; a shower of frozen blossoms; the descent;
mode of attachment; Startling Avalanche; Blue Light emitted
from the fissures of the fresh snow; Stifling Heat; return
to the Riffel
19. 133
The Rothe Kumm; pleasant companions; difficult descent;
temperatures of rock, air, and grass; Singular Cavern in the
ice; Structure and Stratification
20.--The Görner Grat and the Riffelhorn; Magnetic Phenomena. 137
Formation and Dissipation of clouds; Scene from the Görner
Grat; Magnetism of the Rocks; the Compass and Sun at
variance; ascent of the Riffelhorn; Magnetic effects; places
of most intense action; Scratched and Polished Rocks;
Exfoliation of crust produced by the sliding of ancient
glaciers; Magnetic Polarity; Consequent Points; Bearings
from the Riffelhorn; action on a Distant Needle
21. 145
Fog on the Riffelberg; its dissipation; Sunset from the
Görner Grat; Cloud-wreaths on the Matterhorn; Streamers of
Flame; grand Interference Phenomenon; investigation of
Structure; the Görnerhorn glacier; Western glacier of Monte
Rosa; the Schwarze, Trifti, and Théodule glaciers; welding
of the Tributaries to parallel Strips; Temptation
22.--Second Ascent of Monte Rosa (1858). 151
A Light Scrip; my Guide lent; a substitute; a party on the
mountain; across the glacier and up the rocks; the guide
expostulates; among the crevasses; the guide halts; left
alone; beauty of the mountain; splendid effects of
Diffraction; Cheer from the summit; on the Kamm; climbers
meet; among the rocks; Alone on the Summit; the Axe slips;
the prospect; the descent; serious accident; a word on
climbing alone
23. 160
The Furgge glacier; thunder and lightning; the Weissthor
given up; excursion by Stalden to Saas; Herr Imseng; the
Mattmark See and Hotel; ascent of a boulder; Snow-storm;
cold quarters; the Monte Moro; the Allalein glacier; a noble
vault; Structure and Dirt-bands; stormy weather; Avalanches
at Saas; the Fée glacier; Frozen dust on the
Mischabelhörner; Snow, Vapour, and Cloud; curious effect on
the hearing; "a Terrible Hole;" singular group; a Song from
'The Robbers'
24. 168
Need of observations on Alpine Temperature; Balmat's
intention; aid from the Royal Society; Difficulties at
Chamouni in 1858; the Intendant memorialised; his response;
the Séracs revisited; Crevasses and Crumples; bad weather;
thermometers placed at the Jardin; Avalanches of the
Talèfre; wondrous sky
25.--Second Ascent of Mont Blanc (1858). 177
Shadows of the Aiguilles; Silver Trees at sunrise; M.
Necker's letter; Birds as Sparks and Stars against the sky;
crevasse bridged; ladder rejected; a hunt for a _pont_;
crevasses crossed; Magnificent Sunset; illuminated clouds;
Storm on the Grands Mulets; a Comet discovered; start by
starlight; the Petit Plateau a reservoir for avalanches;
Balmat's warning; the Grand Plateau at dawn; blue of the
ice; Balmat in danger; Clouds upon the Calotte; the Summit;
wind and snow-dust; Balmat frostbitten; halt on the Calotte;
descent to Chamouni; good conduct of porters
26. 192
Hostility of Chief Guide; Procès Verbal; the British
Association; application to the Sardinian authorities;
President's Letter; Royal Society; Testimonial to Balmat
27.--Winter Expedition to the Mer de Glace, 1859. 195
First defeat and fresh attempt; Geneva to Chamouni; deep
snow; Desolation; slow progress; a horse in the snow; a
struggle; Chamouni on Christmas night; mountains hidden;
Climb to the Montanvert; Snow on the Pines; débris of
avalanches; Breaking of snow; Atmospheric Changes; the
mountains concealed and revealed; colour of the snow; the
Montanvert in Winter; footprints in the snow; wonderful
frost figures; Crystal Curtain; the Mer de Glace in Winter;
the first night; "a rose of dawn;" Crimson Banners of the
Aiguilles; the stakes fixed; a Hurricane on the glacier; the
second night; Wild Snow-storm; a man in a crevasse; calm;
Magnificent Snow Crystals; Sound through the falling snow;
swift descent; Source of the Arveiron; Crystal Cave;
appearance of water; westward from the vault; Majestic
Scene; Farewell
PART II.
1.--Light and Heat. 223
What is Light?--notion of the ancients; requires Time to
pass through Space; Römer, Bradley, Fizeau; Emission Theory
supported by Newton, opposed by Huyghens; the Wave Theory
established by Young and Fresnel; Theory explained; nature
of Sound; of Music; of Pitch; nature of Light; of Colour;
two sounds may produce silence; two rays of light may
produce darkness; two rays of heat may produce cold; Length
and Number of waves of light; Liquid Waves; Interference;
Diffraction; Colours of Thin Plates; applications of the
foregoing to cloud iridescences, luminous trees, twinkling
of stars, the Spirit of the Brocken, &c.
2.--Radiant Heat. 239
The Sun emits a multitude of Non-luminous Rays; Rays of Heat
differ from rays of Light as one colour differs from
another; the same ray may produce the sensations of light
and heat
3.--Qualities of Heat. 241
Heat a kind of Motion; system of exchanges; Luminous and
Obscure Heat; Absorption by Gases; gases may be transparent
to light, but opaque to heat; Heat selected from luminous
sources; the Atmosphere acts the part of a Ratchet-wheel;
possible heat of a Distant Planet; causes of Cold in the
upper strata of the Earth's Atmosphere
4.--Origin of Glaciers. 248
Application of principles; the Snow-line; its meaning;
waters piled annually in a solid form on the summits of the
hills; the Glaciers furnish the chief means of escape;
superior and inferior snow-line
5. 249
Whiteness of snow; whiteness of ice; Round air-bubbles;
melting and freezing; Conversion of snow into ice by
Pressure
6.--Colour of Water and Ice. 253
Waves of Ether not entangled; they are separated in the
prism; they are differently absorbed; Colour due to this;
Water and Ice blue; water and ice opaque to radiant heat;
Long Waves shivered on the molecules; Experiment; Grotto of
Capri; the Laugs of Iceland
7.--Colours of the Sky. 257
Newton's idea; Goethe's Theory; Clausius and Brücke;
Suspended Particles; singular effect on a painting explained
by Goethe; Light separated without Absorption; Reflected and
Transmitted light; blueness of milk and juices; the Sun
through London smoke; Experiments; Blue of the Eye; Colours
of Steam; the Lake of Geneva
8.--The Moraines. 263
Glacier loaded along its edges by the ruins of the
mountains; Lateral Moraines; Medial Moraines; their number
_one_ less than the number of Tributaries; Moraines of the
Mer de Glace; successive shrinkings; Glacier Tables
explained; 'Dip' of stones upon the glacier enables us to
draw the Meridian Line; type 'Table;' Sand Cones; moraines
engulfed and disgorged; transparency of ice under the
moraines
9.--Glacier Motion,--Preliminary. 269
Névé and Glacier; First Measurements; Hugi and Agassiz;
Escher's defeat on the Aletsch; Piles fixed across the Aar
glacier by Agassiz in 1841; Professor Forbes invited by M.
Agassiz; Forbes's first observations on the Mer de Glace in
1842; motion of Agassiz's piles measured by M. Wild; Centre
of the glacier moves quickest; State of the Question
10.--Motion of the Mer de Glace. 275
The Theodolite; mode of measurement; first line; Centre
Point not the quickest; second line; former result
confirmed; Law of Motion sought; the glacier moves through a
Sinuous Valley; effect of Flexure; Western half of glacier
moves quickest; Point of Maximum Motion crosses axis;
Eastern half moves quickest; Locus of Point of Maximum
Motion; New Law; Motion of the Géant; motion of the Léchaud;
Squeezing of the Tributaries through the Neck of the valley
at Trélaporte; the Léchaud a Driblet
11.--Ice Wall at the Tacul,--Velocities of Top and Bottom. 289
First attempt by Mr. Hirst; second attempt, stakes fixed at
Top, Bottom, and Centre; dense fog; the stakes lost; process
repeated; Velocities determined
12.--Winter Motion of the Mer de Glace. 294
First line, Above the Montanvert; second line, Below the
Montanvert; Ratio of winter to summer motion
13.--Cause of Glacier Motion,--De Saussure's Theory. 296
First attempt at a Theory by Scheuchzer in 1705;
Charpentier's theory, or the Theory of Dilatation; Agassiz's
theory; Altmann and Grüner; theory of De Saussure, or the
Sliding Theory; in part true; strained interpretation of
this theory
14.--Rendu's Theory. 299
Character of Rendu; his Essay entitled 'Théorie des Glaciers
de la Savoie;' extracts from the essay; he ascribes
"circulation" to natural forces; classifies glaciers;
assigns the cause of the conversion of snow into ice;
notices Veined Structure; "time and affinity;" notices
Regelation; diminution of _glaciers réservoirs_; Remarkable
Passage; announces Swifter Motion of Centre; North British
Review; Discrepancies explained by Rendu; Liquid Motion
ascribed to glacier; all the phenomena of a River reproduced
upon the Mer de Glace; Ratio of Side and Central velocities;
Errors removed
15. 308
Anticipations of Rendu confirmed by Agassiz and Forbes;
analogies with Liquid Motion established by Forbes; his
Measurements in 1842; measurements in 1844 and 1846;
Measurements of Agassiz and Wild in 1842, 1843, 1844, and
1845; Agassiz notices the "migration" of the Point of
Swiftest Motion; true meaning of this observation; Summary
of contributions on this part of the question
16.--Forbes's Theory. 311
Discussions as to its meaning; Facts and Principles;
definition of theory; Some Experiments on the Mer de Glace
to test the Viscosity of the Ice
17.--The Crevasses. 315
Caused by the Motion; Ice Sculpture; Fantastic Figures;
beauty of the crevasses of the highest glaciers; Birth of a
crevasse; Mechanical Origin; line of greatest strain;
Marginal Crevasses; Transverse Crevasses; Longitudinal
Crevasses; Bergschrunds; Influence of Flexure; why the
Convex Sides of glaciers are most crevassed
18. 325
Further considerations on Viscosity; Numerical Test;
formation of crevasses opposed to viscosity
19.--Heat and Work. 328
Connexion of Natural Forces; Equivalence of Heat and Work;
heat produced by Mechanical Action; heat consumed in
producing work; Chemical Attractions; Attraction of
Gravitation; amount of heat which would be produced by the
stoppage of the Earth in its Orbit; amount produced by the
falling of the Earth into the Sun; shifting of Atoms; heat
consumed in Molecular Work; Specific Heat; Latent Heat;
'friability' of ice near its melting point; Rotten Ice and
softened Wax
20. 334
Papers presented to the Royal Society by Professor Forbes in
1846; Capillary Hypothesis of glacier motion; hypothesis
examined
21.--Thomson's Theory. 340
Statement of theory; influence of Pressure on the Melting
Point of Ice; difficulties of theory; Calculation of
requisite Pressure; Actual pressure insufficient
22.--Pressure Theory. 346
Pressure and Tension; possible experiments; Ice may be
moulded into Vases and Statuettes or coiled into Knots; this
no proof of Viscosity; Actual Experiments; a sphere of ice
moulded to a lens; a lens moulded to a cylinder; a lump of
ice moulded to a cup; straight bars of ice bent; ice thus
moulded incapable of being sensibly stretched; when Tension
is substituted for Pressure, analogy with viscous body
breaks down
23.--Regelation. 351
Faraday's first experiments; Freezing together of pieces of
ice at 32°; Freezing in Hot Water; Faraday's recent
experiments; Regelation not due to Pressure nor to Capillary
Attraction; it takes place in vacuo; fracture and
regelation; no viscidity discovered
24.--Crystallization and Internal Liquefaction. 353
How crystals are 'nursed;' Snow-Crystals; Crystal Stars
formed in Water; Arrangement of Atoms of Lake Ice;
dissection of ice by a sunbeam; Liquid Flowers formed in
ice; associated Vacuous Spots; curious sounds; their
explanation; Cohesion of water when free from air; liquid
snaps like a broken spring; Ebullition converted into
Explosion; noise of crepitation; Water-cells in glacier ice;
Vacuous Spots mistaken for Bubbles; not Flattened by
Pressure; experiments; Cause of Regelation
25.--The Moulins. 362
Their character; Depth of Moulin on Grindelwald Glacier;
Explanation the Grand Moulin of the Mer de Glace; Motion of
moulins
26.--Dirt-Bands of the Mer de Glace. 367
Their discovery by Professor Forbes; view of Bands from a
point near the Flégère; Bands as seen from Les Charmoz; Skew
Surface of glacier; aspect of Bands from the Cleft Station;
Origin of bands; tendency to become straight; differences
between observers
27.--Veined Structure of Glaciers. 376
General appearance; Grooves upon the glacier; first
observations; description by M. Guyot; observations of
Professor Forbes; Structure and Stratification; subject
examined; Marginal Structure; Transverse Structure;
Longitudinal Structure; experimental illustrations; the
Structure Complementary to the Crevasses; glaciers of the
Oberland, Valais, and Savoy examined with reference to this
question
28.--The Veined Structure and Differential Motion. 395
Marginal Structure Oblique to sides; Drag towards the
centre; difficulties of theory which ascribes the structure
to Differential Sliding; it persists _across_ the lines of
maximum sliding
29.--The Ripple Theory of the Veined Structure. 398
Ripples in Water supposed to correspond to Glacier
Structure; analysis of theory; observation of the MM. Weber;
water dropping from an oar; stream cleft by an obstacle; Two
Divergent lines of Ripple; Single Line produced by Lateral
Obstacle; Direction of ripples compounded of River's motion
and Wave motion; Structure and Ripples due to different
causes; their positions also different
30.--The Veined Structure and Pressure. 404
Supposed case of pressed prism of glass; Experiments of
Nature; Quartz-pebbles flattened and indented; Pressure
would produce Lamination; Tangential Action
31.--The Veined Structure and the Liquefaction of Ice by Pressure. 408
Influence of pressure on Melting and Boiling points; some
substances swell, others shrink in melting; effects of
pressure different on the two classes of bodies; Theoretic
Anticipation by Mr. James Thomson; Melting point of Ice
lowered by pressure; Internal Liquefaction of a prism of
solid ice by pressure; Liquefaction in Layers; application
to the Veined Structure
32.--White Ice-Seams of the Glacier du Géant. 413
Aspect of Seams; they sweep across the glacier concentric
with Structure; Structure at the base of the Talèfre
cascade; Crumples; Scaling off by pressure; Origin of seams
of White Ice
33. 419
Glacier du Géant in a state of Longitudinal Compression;
Measurements which prove that its hinder parts are advancing
upon those in front; Shortening of its Undulations;
Squeezing of white Ice-seams; development of Veined
Structure
Summary 422
Appendix 427
Index 441
ILLUSTRATIONS.
The Mer de Glace.--Showing the Cleft Station at Trélaporte,
the Echelets, the Tacul, the Périades, and the Grand
Jorasse. _Frontispiece_
Fig. Page
1. Ice Minaret 14
2. Diagram of an angular reflector 16
3, 4. Boats' sails inverted by Atmospheric Refraction 35
5. Wave-like forms on the Mer de Glace 43
6. Glacier Table 44
7. Tributaries of the Mer de Glace 53
8. Magnetic Boulder of the Riffelhorn 143
9, 10, 11, 12. Luminous Trees projected against the sky
at sunrise 180, 181
13. Snow on the Pines 201
14, 15. Snow Crystals 214
16. Chasing produced by waves 233
17. Diagram explanatory of Interference 234
18. Interference Spectra, produced by Diffraction _To face_ 235
19. Moraines of the Mer de Glace " 264
20. Typical section of a glacier Table 266
21. Locus of the Point of Maximum Motion 286
22. Inclinations of ice cascade of the Glacier des Bois 313
23. Inclinations of Mer de Glace above l'Angle 314
24. Fantastic Mass of ice 316
25. Diagram explanatory of the mechanical origin of Crevasses 318
26. Diagram showing the line of Greatest Strain 319
27A, B. Section and Plan of a portion of the Lower
Grindelwald Glacier 322
28. Diagram illustrating the crevassing of Convex Sides
of glacier 323
29. Diagram illustrating test of viscosity 326
30, 31, 32, 33. Moulds used in experiments with ice 346-348
34. Liquid Flowers in lake ice 355
35. Dirt-bands of the Mer de Glace, as seen from a
point near the Flégère _To face_ 367
36. Ditto, as seen from les Charmoz " 368
37. Ditto, as seen from the Cleft Station, Trélaporte " 369
38. Plan of Dirt-bands taken from Johnson's 'Physical Atlas' 374
39. Veined Structure on the walls of crevasses 381
40. Figure explanatory of the Marginal Structure 383
41. Plan of part of ice-fall, and of glacier below
it (Glacier of the Rhone) 386
42. Section of ditto 386
43. Figure explanatory of Longitudinal Structure 388
44. Structure and bedding on the Great Aletsch Glacier 391
45, 46. Structure and Stratification on the Furgge glacier 394
47. Diagram illustrating Differential Motion 395
48, 49. Diagrams explanatory of the formation of Ripples 400, 403
50, 51. Appearance of a prism of ice partially liquefied
by Pressure. 410
52, 53. Figures illustrative of compression and liquefaction
of ice. 411
54, 55. Sections of White Ice-seams 414
56, 57. Variations in the Dip of the Veined Structure 414, 415
58. Section of three glacier Crumples 416
59. Wall of a crevasse, with incipient crumpling 416
60. Plan of a Stream on the Glacier du Géant 418
61. Plan of a Seam of White Ice on ditto 418
PART I.
CHIEFLY NARRATIVE.
Ages are your days,
Ye grand expressors of the present tense
And types of permanence;
Firm ensigns of the fatal Being
Amid these coward shapes of joy and grief
That will not bide the seeing.
Hither we bring
Our insect miseries to the rocks,
And the whole flight with pestering wing
Vanish and end their murmuring,
Vanish beside these dedicated blocks.
Emerson
GLACIERS OF THE ALPS.
INTRODUCTORY.
(1.)
In the autumn of 1854 I attended the meeting of the British Association
at Liverpool; and, after it was over, availed myself of my position to
make an excursion into North Wales. Guided by a friend who knew the
country, I became acquainted with its chief beauties, and concluded the
expedition by a visit to Bangor and the neighbouring slate quarries of
Penrhyn.
From my boyhood I had been accustomed to handle slates; had seen them
used as roofing materials, and had worked the usual amount of arithmetic
upon them at school; but now, as I saw the rocks blasted, the broken
masses removed to the sheds surrounding the quarry, and there cloven
into thin plates, a new interest was excited, and I could not help
asking after the cause of this extraordinary property of cleavage. It
sufficed to strike the point of an iron instrument into the edge of a
plate of rock to cause the mass to yield and open, as wood opens in
advance of a wedge driven into it. I walked round the quarry and
observed that the planes of cleavage were everywhere parallel; the rock
was capable of being split in one direction only, and this direction
remained perfectly constant throughout the entire quarry.
[Sidenote: CLEAVAGE OF SLATE ROCKS.]
I was puzzled, and, on expressing my perplexity to my companion, he
suggested that the cleavage was nothing more than the layers in which
the rock had been originally deposited, and which, by some subsequent
disturbance, had been set on end, like the strata of the sandstone rocks
and chalk cliffs of Alum Bay. But though I was too ignorant to combat
this notion successfully, it by no means satisfied me. I did not know
that at the time of my visit this very question of slaty cleavage was
exciting the greatest attention among English geologists, and I quitted
the place with that feeling of intellectual discontent which, however
unpleasant it may be for a time, is very useful as a stimulant, and
perhaps as necessary to the true appreciation of knowledge as a healthy
appetite is to the enjoyment of food.
On inquiry I found that the subject had been treated by three English
writers, Professor Sedgwick, Mr. Daniel Sharpe, and Mr. Sorby. From
Professor Sedgwick I learned that cleavage and stratification were
things totally distinct from each other; that in many cases the strata
could be observed with the cleavage passing through them at a high
angle; and that this was the case throughout vast areas in North Wales
and Cumberland. I read the lucid and important memoir of this eminent
geologist with great interest: it placed the data of the problem before
me, as far as they were then known, and I found myself, to some extent
at least, in a condition to appreciate the value of a theoretic
explanation.
Everybody has heard of the force of gravitation, and of that of
cohesion; but there is a more subtle play of forces exerted by the
molecules of bodies upon each other when these molecules possess
sufficient freedom of action. In virtue of such forces, the ultimate
particles of matter are enabled to build themselves up into those
wondrous edifices which we call crystals. A diamond is a crystal
self-erected from atoms of carbon; an amethyst is a crystal built up
from particles of silica; Iceland spar is a crystal built by particles
of carbonate of lime. By artificial means we can allow the particles of
bodies the free play necessary to their crystallization. Thus a solution
of saltpetre exposed to slow evaporation produces crystals of saltpetre;
alum crystals of great size and beauty may be obtained in a similar
manner; and in the formation of a bit of common sugar-candy there are
agencies at play, the contemplation of which, as mere objects of
thought, is sufficient to make the wisest philosopher bow down in
wonder, and confess himself a child.
[Sidenote: CRYSTALLIZATION THEORY.]
The particles of certain crystalline bodies are found to arrange
themselves in layers, like courses of atomic masonry, and along these
layers such crystals may be easily cloven into the thinnest laminæ. Some
crystals possess _one_ such direction in which they may be cloven, some
several; some, on the other hand, may be split with different facility
in different directions. Rock salt may be cloven with equal facility in
three directions at right angles to each other; that is, it may be split
into cubes; calcspar may be cloven in three directions oblique to each
other; that is, into rhomboids. Heavy spar may also be cloven in three
directions, but one cleavage is much more perfect, or more _eminent_ as
it is sometimes called, than the rest. Mica is a crystal which cleaves
very readily in one direction, and it is sufficiently tough to furnish
films of extreme tenuity: finally, any boy, with sufficient skill, who
tries a good crystal of sugar-candy in various directions with the blade
of his penknife, will find that it possesses one direction in
particular, along which, if the blade of the knife be placed and struck,
the crystal will split into plates possessing clean and shining surfaces
of cleavage.
[Sidenote: POLAR FORCES.]
Professor Sedgwick was intimately acquainted with all these facts, and a
great many more, when he investigated the cleavage of slate rocks; and
seeing no other explanation open to him, he ascribed to slaty cleavage a
crystalline origin. He supposed that the particles of slate rock were
acted on, after their deposition, by "polar forces," which so arranged
them as to produce the cleavage. According to this theory, therefore,
Honister Crag and the cliffs of Penrhyn are to be regarded as portions
of enormous crystals; a length of time commensurate with the vastness of
the supposed action being assumed to have elapsed between the deposition
of the rock and its final crystallization.
When, however, we look closely into this bold and beautiful hypothesis,
we find that the only analogy which exists between the physical
structure of slate rocks and of crystals is this single one of cleavage.
Such a coincidence might fairly give rise to the conjecture that both
were due to a common cause; but there is great difficulty in accepting
this as a theoretic truth. When we examine the structure of a slate
rock, we find that the substance is composed of the débris of former
rocks; that it was once a fine mud, composed of particles of _sensible
magnitude_. Is it meant that these particles, each taken as a whole,
were re-arranged after deposition? If so, the force which effected such
an arrangement must be wholly different from that of crystallization,
for the latter is essentially _molecular_. What is this force? Nature,
as far as we know, furnishes none competent, under the conditions, to
produce the effect. Is it meant that the molecules composing these
sensible particles have re-arranged themselves? We find no evidence of
such an action in the individual fragments: the mica is still mica, and
possesses all the properties of mica; and so of the other ingredients of
which the rock is composed. Independent of this, that an aggregate of
heterogeneous mineral fragments should, without any assignable external
cause, so shift its molecules as to produce a plane of cleavage common
to them all, is, in my opinion, an assumption too heavy for any theory
to bear.
Nevertheless, the paper of Professor Sedgwick invested the subject of
slaty cleavage with an interest not to be forgotten, and proved the
stimulus to further inquiry. The structure of slate rocks was more
closely examined; the fossils which they contained were subjected to
rigid scrutiny, and their shapes compared with those of the same species
taken from other rocks. Thus proceeding, the late Mr. Daniel Sharpe
found that the fossils contained in slate rocks are distorted in shape,
being uniformly flattened out in the direction of the planes of
cleavage. Here, then, was a fact of capital importance,--the shells
became the indicators of an action to which the mass containing them had
been subjected; they demonstrated the operation of pressure acting at
right angles to the planes of cleavage.
[Sidenote: MECHANICAL THEORY.]
The more the subject was investigated, the more clearly were the
evidences of pressure made out. Subsequent to Mr. Sharpe, Mr. Sorby
entered upon this field of inquiry. With great skill and patience he
prepared sections of slate rock, which he submitted to microscopic
examination, and his observations showed that the evidences of pressure
could be plainly traced, even in his minute specimens. The subject has
been since ably followed up by Professors Haughton, Harkness, and
others; but to the two gentlemen first mentioned we are, I think,
indebted for the prime facts on which rests the _mechanical theory_ of
slaty cleavage.[A]
[Sidenote: LECTURE AT THE ROYAL INSTITUTION.]
The observations just referred to showed the co-existence of the two
phenomena, but they did not prove that pressure and cleavage stood to
each other in the relation of cause and effect. "Can the pressure
produce the cleavage?" was still an open question, and it was one which
mere reasoning, unaided by experiment, was incompetent to answer.
Sharpe despaired of an experimental solution, regarding our means as
inadequate, and our time on earth too short to produce the result. Mr.
Sorby was more hopeful. Submitting mixtures of gypsum and oxide of iron
scales to pressure, he found that the scales set themselves
approximately at right angles to the direction in which the pressure was
applied. The position of the scales resembled that of the plates of mica
which his researches had disclosed to him in slate rock, and he inferred
that the presence of such plates, and of flat or elongated fragments
generally, lying all in the same general direction, was the cause of
slaty cleavage. At the meeting of the British Association at Glasgow, in
1855, I had the pleasure of seeing some of Mr. Sorby's specimens, and,
though the cleavage they exhibited was very rough, still, the tendency
to yield at right angles to the direction in which the pressure had been
applied, appeared sufficiently manifest.
At the time now referred to I was engaged, and had been for a long time
previously, in examining the effects of pressure upon the magnetic
force, and, as far back as 1851, I had noticed that some of the bodies
which I had subjected to pressure exhibited a cleavage of surpassing
beauty and delicacy. The bearing of such facts upon the present question
now forcibly occurred to me. I followed up the observations; visited
slate yards and quarries, observed the exfoliation of rails, the fibres
of iron, the structure of tiles, pottery, and cheese, and had several
practical lessons in the manufacture of puff-paste and other laminated
confectionery. My observations, I thought, pointed to a theory of slaty
cleavage different from any previously given, and which, moreover,
referred a great number of apparently unrelated phenomena to a common
cause. On the 10th of June, 1856, I made them the subject of a Friday
evening's discourse at the Royal Institution.[B]
[Sidenote: ORIGIN OF RESEARCHES.]
Such are the circumstances, apparently remote enough, under which my
connexion with glaciers originated. My friend Professor Huxley was
present at the lecture referred to: he was well acquainted with the work
of Professor Forbes, entitled 'Travels in the Alps,' and he surmised
that the question of slaty cleavage, in its new aspect, might have some
bearing upon the laminated structure of glacier-ice discussed in the
work referred to. He therefore urged me to read the 'Travels,' which I
did with care, and the book made the same impression upon me that it had
produced upon my friend. We were both going to Switzerland that year,
and it required but a slight modification of our plans to arrange a
joint excursion over some of the glaciers of the Oberland, and thus
afford ourselves the means of observing together the veined structure of
the ice.
Had the results of this arrangement been revealed to me beforehand, I
should have paused before entering upon an investigation which required
of me so long a renunciation of my old and more favourite pursuits. But
no man knows when he commences the examination of a physical problem
into what new and complicated mental alliances it may lead him. No
fragment of nature can be studied alone; each part is related to every
other part; and hence it is, that, following up the links of law which
connect phenomena, the physical investigator often finds himself led far
beyond the scope of his original intentions, the danger in this respect
augmenting in direct proportion to the wish of the inquirer to render
his knowledge solid and complete.
[Sidenote: A BOY'S BOOK.]
When the idea of writing this book first occurred to me, it was not my
intention to confine myself to the glaciers alone, but to make the work
a vehicle for the familiar explanation of such general physical
phenomena as had come under my notice. Nor did I intend to address it to
a cultured man of science, but to a youth of average intelligence, and
furnished with the education which England now offers to the young. I
wished indeed to make it a boy's class-book, which should reveal the
mode of life, as well as the scientific objects, of an explorer of the
Alps. The incidents of the past year have caused me to deviate, in some
degree, from this intention, but its traces will be sufficiently
manifest; and this reference to it will, I trust, excuse an occasional
liberty of style and simplicity of treatment which would be out of place
if intended for a reader of riper years.
FOOTNOTES:
[A] Mr. Sorby has drawn my attention to an able and interesting paper by
M. Bauer, in Karsten's 'Archiv' for 1846; in which it is announced that
cleavage is a tension of the mass _produced by pressure_. The author
refers to the experiments of Mr. Hopkins as bearing upon the question.
[B] See Appendix.
[Sidenote: THE OBERLAND. 1856.]
EXPEDITION OF 1856.
THE OBERLAND.
(2.)
On the 16th of August, 1856, I received my Alpenstock from the hands of
Dr. Hooker, in the garden of the Pension Ober, at Interlaken. It bore my
name, not marked, however, by the vulgar brands of the country, but by
the solar beams which had been converged upon it by the pocket lens of
my friend. I was the companion of Mr. Huxley, and our first aim was to
cross the Wengern Alp. Light and shadow enriched the crags and green
slopes as we advanced up the valley of Lauterbrunnen, and each occupied
himself with that which most interested him. My companion examined the
drift, I the cleavage, while both of us looked with interest at the
contortions of the strata to our left, and at the shadowy, unsubstantial
aspect of the pines, gleaming through the sunhaze to our right.
[Sidenote: FOLDED ROCKS. 1856.]
What was the physical condition of the rock when it was thus bent and
folded like a pliant mass? Was it necessarily softer than it is at
present? I do not think so. The shock which would crush a railway
carriage, if communicated to it at once, is harmless when distributed
over the interval necessary for the pushing in of the buffer. By
suddenly stopping a cock from which water flows you may burst the
conveyance pipe, while a slow turning of the cock keeps all safe. Might
not a solid rock by ages of pressure be folded as above? It is a
physical axiom that no body is perfectly hard, none perfectly soft, none
perfectly elastic. The hardest body subjected to pressure yields,
however little, and the same body when the pressure is removed cannot
return to its original form. If it did not yield in the slightest degree
it would be perfectly hard; if it could completely return to its
original shape it would be perfectly elastic.
Let a pound weight be placed upon a cube of granite; the cube is
flattened, though in an infinitesimal degree. Let the weight be removed,
the cube _remains_ a little flattened; it cannot quite return to its
primitive condition. Let us call the cube thus flattened No. 1. Starting
with No. 1 as a new mass, let the pound weight be laid upon it; the mass
yields, and on removing the weight it cannot return to the dimensions of
No. 1; we have a more flattened mass, No. 2. Proceeding in this manner,
it is manifest that by a repetition of the process we should produce a
series of masses, each succeeding one more flattened than the former.
This appears to be a necessary consequence of the physical axiom
referred to above.
Now if, instead of removing and replacing the weight in the manner
supposed, we cause it to rest continuously upon the cube, the
flattening, which above was intermittent, will be continuous; no matter
how hard the cube may be, there will be a gradual yielding of its mass
under the pressure. Apply this to squeezed rocks--to those, for example,
which form the base of an obelisk like the Matterhorn; that this base
must yield, seems a certain consequence of the physical constitution of
matter: the conclusion seems inevitable that the mountain is sinking by
its own weight. Let two points be fixed, one near the summit, the other
near the base of the obelisk; next year these points will have
approached each other. Whether the amount of approach in a human
lifetime be measureable we know not; but it seems certain that ages
would leave their impress upon the mass, and render visible to the eye
an action which at present is appreciable by the imagination only.
[Sidenote: THE JUNGFRAU AND SILBERHORN. 1856.]
We halted on the night of the 16th at the Jungfrau Hotel, and next
morning we saw the beams of the rising sun fall upon the peaked snow of
the Silberhorn. Slowly and solemnly the pure white cone appeared to rise
higher and higher into the sunlight, being afterwards mottled with gold
and gloom, as clouds drifted between it and the sun. I descended alone
towards the base of the mountain, making my way through a rugged gorge,
the sides of which were strewn with pine-trees, splintered, broken
across, and torn up by the roots. I finally reached the end of a
glacier, formed by the snow and shattered ice which fall from the
shoulders of the Jungfrau. The view from this place had a savage
magnificence such as I had not previously beheld, and it was not without
some slight feeling of awe that I clambered up the end of the glacier.
It was the first I had actually stood upon. The loneliness of the place
was very impressive, the silence being only broken by fitful gusts of
wind, or by the weird rattle of the débris which fell at intervals from
the melting ice.
[Sidenote: AVALANCHES. 1856.]
Once I noticed what appeared to be the sudden and enormous augmentation
of the waters of a cascade, but the sound soon informed me that the
increase was due to an avalanche which had chosen the track of the
cascade for its rush. Soon afterwards my eyes were fixed upon a white
slope some thousands of feet above me; I saw the ice give way, and,
after a sensible interval, the thunder of another avalanche reached me.
A kind of zigzag channel had been worn on the side of the mountain, and
through this the avalanche rushed, hidden at intervals, and anon
shooting forth, and leaping like a cataract down the precipices. The
sound was sometimes continuous, but sometimes broken into rounded
explosions which seemed to assert a passionate predominance over the
general level of the roar. These avalanches, when they first give way,
usually consist of enormous blocks of ice, which are more and more
shattered as they descend. Partly to the echoes of the first crash, but
mainly, I think, to the shock of the harder masses which preserve their
cohesion, the explosions which occur during the descent of the avalanche
are to be ascribed. Much of the ice is crushed to powder; and thus, when
an avalanche pours cataract-like over a ledge, the heavier masses, being
less influenced by the atmospheric resistance, shoot forward like
descending rockets, leaving the lighter powder in trains behind them.
Such is the material of which a class of the smaller glaciers in the
Alps is composed. They are the products of avalanches, the crushed ice
being recompacted into a solid mass, which exhibits on a smaller scale
most of the characteristics of the large glaciers.
After three hours' absence I reascended to the hotel, breakfasted, and
afterwards returned with Mr. Huxley to the glacier. While we were
engaged upon it the weather suddenly changed; lightning flashed about
the summits of the Jungfrau, and thunder "leaped" among her crags. Heavy
rain fell, but it cleared up afterwards with magical speed, and we
returned to our hotel. Heedless of the forebodings of many prophets of
evil weather we set out for Grindelwald. The scene from the summit of
the Little Scheideck was exceedingly grand. The upper air exhibited a
commotion which we did not experience; clouds were wildly driven against
the flanks of the Eiger, the Jungfrau thundered behind, while in front
of us a magnificent rainbow, fixing one of its arms in the valley of
Grindelwald, and, throwing the other right over the crown of the
Wetterhorn, clasped the mountain in its embrace. Through jagged
apertures in the clouds floods of golden light were poured down the
sides of the mountain. On the slopes were innumerable chalets,
glistening in the sunbeams, herds browsing peacefully and shaking their
mellow bells; while the blackness of the pine-trees, crowded into
woods, or scattered in pleasant clusters over alp and valley, contrasted
forcibly with the lively green of the fields.
[Sidenote: THE HEISSE PLATTE. 1856.]
At Grindelwald, on the 18th, we engaged a strong and competent guide,
named Christian Kaufmann, and proceeded to the Lower Glacier. After a
steep ascent, we gained a point from which we could look down upon the
frozen mass. At first the ice presented an appearance of utter
confusion, but we soon reached a position where the mechanical
conditions of the glacier revealed themselves, and where we might learn,
had we not known it before, that confusion is merely the unknown
intermixture of laws, and becomes order and beauty when we rise to their
comprehension. We reached the so-called Eismeer--Ice Sea. In front of us
was the range of the Viescherhörner, and a vast snow slope, from which
one branch of the glacier was fed. Near the base of this _névé_, and
surrounded on all sides by ice, lay a brown rock, to which our attention
was directed as a place noted for avalanches; on this rock snow or ice
never rests, and it is hence called the _Heisse Platte_--the Hot Plate.
At the base of the rock, and far below it, the glacier was covered with
clean crushed ice, which had fallen from a crown of frozen cliffs
encircling the brow of the rock. One obelisk in particular signalised
itself from all others by its exceeding grace and beauty. Its general
surface was dazzling white, but from its clefts and fissures issued a
delicate blue light, which deepened in hue from the edges inwards. It
stood upon a pedestal of its own substance, and seemed as accurately
fixed as if rule and plummet had been employed in its erection. Fig. 1
represents this beautiful minaret of ice.
[Sidenote: ICE MINARET. 1856.]
[Illustration: Fig. 1. Ice Minaret.]
While we were in sight of the Heisse Platte, a dozen avalanches rushed
downwards from its summit. In most cases we were informed of the descent
of an avalanche by the sound, but sometimes the white mass was seen
gliding down the rock, and scattering its _smoke_ in the air, long
before the sound reached us. It is difficult to reconcile the
insignificant appearance presented by avalanches, when seen from a
distance, with the volume of sound which they generate; but on this day
we saw sufficient to account for the noise. One block of solid ice which
we found below the Heisse Platte measured 7 feet 6 inches in length, 5
feet 8 inches in height, and 4 feet 6 inches in depth. A second mass was
10 feet long, 8 feet high, and 6 feet wide. It contained therefore 480
cubic feet of ice, which had been cast to a distance of nearly 1000
yards down the glacier. The shock of such hard and ponderous projectiles
against rocks and ice, reinforced by the echoes from the surrounding
mountains, will appear sufficient to account for the peals by which
their descent is accompanied.
[Sidenote: ECHOES OF THE WETTERHORN. 1856.]
A second day, in company with Dr. Hooker, completed the examination of
this glacier in 1856; after which I parted from my friends, Mr. Huxley
intending to rejoin me at the Grimsel. On the morning of the 20th of
August I strapped on my knapsack and ascended the green slopes from
Grindelwald towards the Great Scheideck. Before reaching the summit I
frequently heard the wonderful echoes of the Wetterhorn. Some travellers
were in advance of me, and to amuse them an alpine horn was blown. The
direct sound was cut off from me by a hill, but the echoes talked down
to me from the mountain walls. The sonorous waves arrived after one,
two, three, and more reflections, diminishing gradually in intensity,
but increasing in softness, as if in its wanderings from crag to crag
the sound had undergone a kind of sifting process, leaving all its
grossness behind, and returning in delightful flute notes to the ear.
Let us investigate this point a little. If two looking-glasses be placed
perfectly parallel to each other, with a lighted candle between them, an
infinite series of images of the candle will be seen at both sides, the
images diminishing in brightness the further they recede. But if the
looking-glasses, instead of being parallel, enclose an angle, a limited
number of images only will be seen. The smaller the angle which the
reflectors make with each other, or, in other words, the nearer they
approach parallelism, the greater will be the number of images observed.
To find the number of images the following is the rule:--Divide 360, or
the number of degrees in a circle, by the number of degrees in the angle
enclosed by the two mirrors, the quotient will be _one more_ than the
number of images; or, counting the object itself, the quotient is always
equal to the number of images plus the object. In Fig. 2 I have given
the number and position of the images produced by two mirrors placed at
an angle of 45°. A B and B C mark the edges of the mirrors, and 0
represents the candle, which, for the sake of simplicity, I have placed
midway between them. Fix one point of a pair of compasses at B, and with
the distance B 0 sweep a circle:--_all the images will be ranged upon
the circumference of this circle_. The number of images found by the
foregoing rule is 7, and their positions are marked in the figure by the
numbers 1, 2, 3, &c.
[Illustration: Fig. 2. Diagram of an angular reflector.]
[Sidenote: ECHOES EXPLAINED. 1856.]
Suppose the _ear_ to occupy the place of the eye, and that _a sounding
body_ occupies the place of the luminous one, we should then have just
as many _echoes_ as we had _images_ in the former case. These echoes
would diminish in loudness just as the images of the candle diminish in
brightness. At each reflection a portion both of sound and light is
lost; hence the oftener light is reflected the dimmer it becomes, and
the oftener sound is reflected the fainter it is.
Now the cliffs of the Wetterhorn are so many rough angular reflectors of
the sound: some of them send it back directly to the listener, and we
have a first echo; some of them send it on to others from which it is
again reflected, forming a second echo. Thus, by repeated reflection,
successive echoes are sent to the ear, until, at length, they become so
faint as to be inaudible. The sound, as it diminishes in intensity,
appears to come from greater and greater distances, as if it were
receding into the mountain solitudes; the final echoes being
inexpressibly soft and pure.
[Sidenote: REICHENBACH AND HANDECK. 1856.]
After crossing the Scheideck I descended to Meyringen, visiting the
Reichenbach waterfall on my way. A peculiarity of the descending water
here is, that it is broken up in one of the basins into nodular masses,
each of which in falling leaves the light foaming mass which surrounds
it as a train in the air behind; the effect exactly resembles that of
the avalanches of the Jungfrau, in which the more solid blocks of ice
shoot forward in advance of the lighter débris, which is held back by
the friction of the air.
Next day I ascended the valley of Hasli, and observed upon the rocks and
mountains the action of ancient glaciers which once filled the valley to
the height of more than a thousand feet above its present level. I
paused, of course, at the waterfall of Handeck, and stood for a time
upon the wooden bridge which spans the river at its top. The Aar comes
gambolling down to the bridge from its parent glacier, takes one short
jump upon a projecting ledge, boils up into foam, and then leaps into a
chasm, from the bottom of which its roar ascends through the gloom. A
rivulet named the Aarlenbach joins the Aar from the left in the very
jaws of the chasm: falling, at first, upon a projection at some depth
below the edge, and, rebounding from this, it darts at the Aar, and both
plunge together like a pair of fighting demons to the bottom of the
gorge. The foam of the Aarlenbach is white, that of the Aar is yellow,
and this enables the observer to trace the passage of the one cataract
_through_ the other. As I stood upon the bridge the sun shone brightly
upon the spray and foam; my shadow was oblique to the river, and hence a
symmetrical rainbow could not be formed in the spray, but one half of a
lovely bow, with its base in the chasm, leaned over against the opposite
rocks, the colours advancing and retreating as the spray shifted its
position. I had been watching the water intently for some time, when a
little Swiss boy, who stood beside me, observed, in his trenchant
German, "There plunge stones ever downwards." The stones were palpable
enough, carried down by the cataract, and sometimes completely breaking
loose from it, but I did not see them until my attention was withdrawn
from the water.
[Sidenote: HUT OF M. DOLLFUSS. 1856.]
On my arrival at the Grimsel I found Mr. Huxley already there, and,
after a few minutes' conversation, we decided to spend a night in a hut
built by M. Dollfuss in 1846, beside the Unteraar glacier, about 2000
feet above the Hospice. We hoped thus to be able to examine the glacier
to its origin on the following day. Two days' food and some blankets
were sent up from the Hospice, and, accompanied by our guide, we
proceeded to the glacier.
[Sidenote: HÔTEL DES NEUFCHÂTELOIS. 1856.]
Having climbed a great terminal moraine, and tramped for a considerable
time amid loose shingle and boulders, we came upon the ice. The finest
specimens of "tables" which I have ever seen are to be found upon this
glacier--huge masses of clean granite poised on pedestals of ice. Here
are also "dirt-cones" of the largest size, and numerous shafts, the
forsaken passages of ancient "moulins," some filled with water, others
simply with deep blue light. I reserve the description and explanation
of both cones and moulins for another place. The surfaces of some of the
small pools were sprinkled lightly over with snow, which the water
underneath was unable to melt; a coating of snow granules was thus
formed, flexible as chain armour, but so close that the air could not
escape through it. Some bubbles which had risen through the water had
lifted the coating here and there into little rounded domes, which, by
gentle pressure, could be shifted hither and thither, and several of
them collected into one. We reached the hut, the floor of which appeared
to be of the original mountain slab; there was a space for cooking
walled off from the sleeping-room, half of which was raised above the
floor, and contained a quantity of old hay. The number 2404 mètres, the
height, I suppose, of the place above the sea, was painted on the
door, behind which were also the names of several well-known
observers--Agassiz, Forbes, Desor, Dollfuss, Ramsay, and others--cut in
the wood. A loft contained a number of instruments for boring, a
surveyor's chain, ropes, and other matters. After dinner I made my way
alone towards the junction of the Finsteraar and Lauteraar glaciers,
which unite at the Abschwung to form the trunk stream of the Unteraar
glacier. Upon the great central moraine which runs between the branches
were perched enormous masses of rock, and, under the overhanging ledge
of one of these, M. Agassiz had his _Hôtel des Neufchâtelois_. The rock
is still there, bearing traces of names now nearly obliterated by the
weather, while the fragments around also bear inscriptions. There in the
wilderness, in the gray light of evening, these blurred and faded
evidences of human activity wore an aspect of sadness. It was a temple
of science now in ruins, and I a solitary pilgrim to the desecrated
blocks. As the day declined, rain began to fall, and I turned my face
towards my new home; where in due time we betook ourselves to our hay,
and waited hopefully for the morning.
But our hopes were doomed to disappointment. A vast quantity of snow
fell during the night, and, when we arose, we found the glacier covered,
and the air thick with the descending flakes. We waited, hoping that it
might clear up, but noon arrived and passed without improvement; our
fire-wood was exhausted, the weather intensely cold, and, according to
the men's opinion, hopelessly bad; they opposed the idea of ascending
further, and we had therefore no alternative but to pack up and move
downwards. What was snow at the higher elevations changed to rain lower
down, and drenched us completely before we reached the Grimsel. But
though thus partially foiled in our design, this visit taught us much
regarding the structure and general phenomena of the glacier.
[Sidenote: THE RHONE GLACIER. 1856.]
The morning of the 24th was clear and calm: we rose with the sun,
refreshed and strong, and crossed the Grimsel pass at an early hour. The
view from the summit of the pass was lovely in the extreme; the sky a
deep blue, the surrounding summits all enamelled with the newly-fallen
snow, which gleamed with dazzling whiteness in the sunlight. It was
Sunday, and the scene was itself a Sabbath, with no sound to disturb its
perfect rest. In a lake which we passed the mountains were mirrored
without distortion, for there was no motion of the air to ruffle its
surface. From the summit of the Mayenwand we looked down upon the Rhone
glacier, and a noble object it seemed,--I hardly know a finer of its
kind in the Alps. Forcing itself through the narrow gorge which holds
the ice cascade in its jaws, and where it is greatly riven and
dislocated, it spreads out in the valley below in such a manner as
clearly to reveal to the mind's eye the nature of the forces to which it
is subjected. Longfellow's figure is quite correct; the glacier
resembles a vast gauntlet, of which the gorge represents the wrist;
while the lower glacier, cleft by its fissures into finger-like ridges,
is typified by the hand.
Furnishing ourselves with provisions at the adjacent inn, we devoted
some hours to the examination of the lower portion of the glacier. The
dirt upon its surface was arranged in grooves as fine as if produced by
the passage of a rake, while the laminated structure of the deeper ice
always corresponded to the superficial grooving. We found several
shafts, some empty, some filled with water. At one place our attention
was attracted by a singular noise, evidently produced by the forcing of
air and water through passages in the body of the glacier; the sound
rose and fell for several minutes, like a kind of intermittent snore,
reminding one of Hugi's hypothesis that the glacier was alive.
[Sidenote: RINGS AROUND THE SUN. 1856.]
We afterwards climbed to a point from which the whole glacier was
visible to us from its origin to its end. Adjacent to us rose the mighty
mass of the Finsteraarhorn, the monarch of the Oberland. The Galenstock
was also at hand, while round about the _névé_ of the glacier a mountain
wall projected its jagged outline against the sky. At a distance was the
grand cone of the Weisshorn, then, and I believe still, unscaled;[A]
further to the left the magnificent peaks of the Mischabel; while
between them, in savage isolation, stood the obelisk of the Matterhorn.
Near us was the chain of the Furca, all covered with shining snow, while
overhead the dark blue of the firmament so influenced the general scene
as to inspire a sentiment of wonder approaching to awe. We descended to
the glacier, and proceeded towards its source. As we advanced an unusual
light fell upon the mountains, and looking upwards we saw a series of
coloured rings, drawn like a vivid circular rainbow quite round the sun.
Between the orb and us spread a thin veil of cloud on which the circles
were painted; the western side of the veil soon melted away, and with it
the colours, but the eastern half remained a quarter of an hour longer,
and then in its turn disappeared. The crevasses became more frequent and
dangerous as we ascended. They were usually furnished with overhanging
eaves of snow, from which long icicles depended, and to tread on which
might be fatal. We were near the source of the glacier, but the time
necessary to reach it was nevertheless indefinite, so great was the
entanglement of fissures. We followed one huge chasm for some hundreds
of yards, hoping to cross it; but after half an hour's fruitless effort
we found ourselves baffled and forced to retrace our steps.
[Sidenote: SPIRIT OF THE BROCKEN. 1856.]
The sun was sloping to the west, and we thought it wise to return; so
down the glacier we went, mingling our footsteps with the tracks of
chamois, while the frightened marmots piped incessantly from the rocks.
We reached the land once more, and halted for a time to look upon the
scene within view. The marvellous blueness of the sky in the earlier
part of the day indicated that the air was charged, almost to
saturation, with transparent aqueous vapour. As the sun sank the shadow
of the Finsteraarhorn was cast through the adjacent atmosphere, which,
thus deprived of the direct rays, curdled up into visible fog. The
condensed vapour moved slowly along the flanks of the mountain, and
poured itself cataract-like into the valley of the Rhone. Here it met
the sun again, which reduced it once more to the invisible state. Thus,
though there was an incessant supply from the generator behind, the fog
made no progress; as in the case of the moving glacier, the end of the
cloud-river remained stationary where consumption was equal to supply.
Proceeding along the mountain to the Furca, we found the valley at the
further side of the pass also filled with fog, which rose, like a wall,
high above the region of actual shadow. Once on turning a corner an
exclamation of surprise burst simultaneously from my companion and
myself. Before each of us and against the wall of fog, stood a spectral
image of a man, of colossal dimensions; dark as a whole, but bounded by
a coloured outline. We stretched forth our arms; the spectres did the
same. We raised our alpenstocks; the spectres also flourished their
bâtons. All our actions were imitated by these fringed and gigantic
shades. We had, in fact, _the Spirit of the Brocken_ before us in
perfection.
At the time here referred to I had had but little experience of alpine
phenomena. I had been through the Oberland in 1850, but was then too
ignorant to learn much from my excursion. Hence the novelty of this
day's experience may have rendered it impressive: still even now I think
there was an intrinsic grandeur in its phenomena which entitles the day
to rank with the most remarkable that I have spent among the Alps. At
the Furca, to my great regret, the joint ramblings of my friend and
myself ended; I parted from him on the mountain side, and watched him
descending, till the gray of evening finally hid him from my view.
FOOTNOTES:
[A] The Weisshorn was first scaled, by Tyndall, in 1861.--L. C. T.
[Sidenote: THE TYROL. 1856.]
THE TYROL.
(3.)
My subsequent destination was Vienna; but I wished to associate with my
journey thither a visit to some of the glaciers of the Tyrol. At
Landeck, on the 29th of August, I learned that the nearest glacier was
that adjacent to the Gebatsch Alp, at the head of the Kaunserthal; and
on the following morning I was on my way towards this valley. I sought
to obtain a guide at Kaltebrunnen, but failed; and afterwards walked to
the little hamlet of Feuchten, where I put up at a very lonely inn. My
host, I believe, had never seen an Englishman, but he had heard of such,
and remarked to me in his patois with emphasis, "_Die Engländer sind die
kühnsten Leute in dieser Welt._" Through his mediation I secured a
chamois-hunter, named Johann Auer, to be my guide, and next morning I
started with this man up the valley. The sun, as we ascended, smote the
earth and us with great power; high mountains flanked us on either side,
while in front of us, closing the view, was the mass of the Weisskugel,
covered with snow. At three o'clock we came in sight of the glacier,
and soon afterwards I made the acquaintance of the _Senner_ or
cheesemakers of the Gebatsch Alp.
[Sidenote: THE GEBATSCH ALP. 1856.]
The chief of these was a fine tall fellow, with free, frank countenance,
which, however, had a dash of the mountain wildness in it. His feet were
bare, he wore breeches, and fragments of stockings partially covered his
legs, leaving a black zone between the upper rim of the sock and the
breeches. His feet and face were of the same swarthy hue; still he was
handsome, and in a measure pleasant to look upon. He asked me what he
could cook for me, and I requested some bread and milk; the former was a
month old, the latter was fresh and delicious, and on these I fared
sumptuously. I went to the glacier afterwards with my guide, and
remained upon the ice until twilight, when we returned, guided by no
path, but passing amid crags grasped by the gnarled roots of the pine,
through green dells, and over bilberry knolls of exquisite colouring. My
guide kept in advance of me singing a Tyrolese melody, and his song and
the surrounding scene revived and realised all the impressions of my
boyhood regarding the Tyrol.
Milking was over when we returned to the chalet, which now contained
four men exclusive of myself and my guide. A fire of pine logs was made
upon a platform of stone, elevated three feet above the floor; there was
no chimney, as the smoke found ample vent through the holes and fissures
in the sides and roof. The men were all intensely sunburnt, the
legitimate brown deepening into black with beard and dirt. The chief
senner prepared supper, breaking eggs into a dish, and using his black
fingers to empty the shell when the albumen was refractory. A fine erect
figure he was as he stood in the glowing light of the fire. All the men
were smoking, and now and then a brand was taken from the fire to light
a renewed pipe, and a ruddy glare flung thereby over the wild
countenance of the smoker. In one corner of the chalet, and raised high
above the ground, was a large bed, covered with clothes of the most
dubious black-brown hue; at one end was a little water-wheel turned by a
brook, which communicated motion to a churndash which made the butter.
The beams and rafters were covered with cheeses, drying in the warm
smoke. The senner, at my request, showed me his storeroom, and explained
to me the process of making cheese, its interest to me consisting in its
bearing upon the question of slaty cleavage. Three gigantic masses of
butter were in the room, and I amused my host by calling them
butter-glaciers. Soon afterwards a bit of cotton was stuck in a lump of
grease, which was placed in a lantern, and the wick ignited; the
chamois-hunter took it, and led the way to our resting-place, I having
previously declined a good-natured invitation to sleep in the big black
bed already referred to.
[Sidenote: AN ALPINE CHALET. 1856.]
There was a cowhouse near the chalet, and above it, raised on pillars of
pine, and approached by a ladder, was a loft, which contained a quantity
of dry hay: this my guide shook to soften the lumps, and erected an
eminence for my head. I lay down, drawing my plaid over me, but Auer
affirmed that this would not be a sufficient protection against the
cold; he therefore piled hay upon me to the shoulders, and proposed
covering up my head also. This, however, I declined, though the biting
coldness of the air, which sometimes blew in upon us, afterwards proved
to me the wisdom of the suggestion. Having set me right, my
chamois-hunter prepared a place for himself, and soon his heavy
breathing informed me that he was in a state of bliss which I could only
envy. One by one the stars crossed the apertures in the roof. Once the
Pleiades hung above me like a cluster of gems; I tried to admire them,
but there was no fervour in my admiration. Sometimes I dozed, but
always as this was about to deepen into positive sleep it was rudely
broken by the clamour of a group of pigs which occupied the ground-floor
of our dwelling. The object of each individual of the group was to
secure for himself the maximum amount of heat, and hence the outside
members were incessantly trying to become inside ones. It was the
struggle of radical and conservative among the pachyderms, the politics
being determined by the accident of position.
[Sidenote: THE GEBATSCH GLACIER. 1856.]
I rose at five o'clock on the 1st of September, and after a breakfast of
black bread and milk ascended the glacier as far as practicable. We once
quitted it, crossed a promontory, and descended upon one of its
branches, which was flanked by some fine old moraines. We here came upon
a group of seven marmots, which with yells of terror scattered
themselves among the rocks. The points of the glacier beyond my reach I
examined through a telescope; along the faces of the sections the lines
of stratification were clearly shown; and in many places where the mass
showed manifest signs of lateral pressure, I thought I could observe the
cleavage passing though the strata. The point, however, was too
important to rest upon an observation made from such a distance, and I
therefore abstained from mentioning it subsequently. I examined the
fissures and the veining, and noticed how the latter became most perfect
in places where the pressure was greatest. The effect of _oblique_
pressure was also finely shown: at one place the thrust of the
descending glacier was opposed by the resistance offered by the side of
the valley, the direction of the force being oblique to the side; the
consequence was a structure nearly parallel to the valley, and
consequently oblique to the thrust which I believe to be its cause.
[Sidenote: A CHAMOIS ON THE ROCKS. 1856.]
After five hours' examination we returned to our chalet, where we
refreshed ourselves, put our things in order, and faced a nameless
"Joch," or pass; our aim being to cross the mountains into the valley of
Lantaufer, and reach Graun that evening. After a rough ascent over the
alp we came to the dead crag, where the weather had broken up the
mountains into ruinous heaps of rock and shingle. We reached the end of
a glacier, the ice of which was covered by sloppy snow, and at some
distance up it came upon an islet of stones and débris, where we paused
to rest ourselves. My guide, as usual, ranged over the summits with his
telescope, and at length exclaimed, "I see a chamois." The creature
stood upon a cliff some hundreds of yards to our left, and seemed to
watch our movements. It was a most graceful animal, and its life and
beauty stood out in forcible antithesis to the surrounding savagery and
death.
On the steep slopes of the glacier I was assisted by the hand of my
guide. In fact, on this day I deemed places dangerous, and dreaded them
as such, which subsequent practice enabled me to regard with perfect
indifference; so much does what we call courage depend upon habit, or on
the fact of knowing that we have really nothing to fear. Doubtless there
are times when a climber has to make up his mind for very unpleasant
possibilities, and even gather calmness from the contemplation of the
worst; but in most cases I should say that his courage is derived from
the latent feeling that the chances of safety are immensely in his
favour.
[Sidenote: PASSAGE OF A JOCH. 1856.]
After a tough struggle we reached the narrow row of crags which form the
crest of the pass, and looked into the world of mountain and cloud on
the other side. The scene was one of stern grandeur--the misty lights
and deep cloud-glooms being so disposed as to augment the impression of
vastness which the scene conveyed. The breeze at the summit was
exceedingly keen, but it gave our muscles tone, and we sprang swiftly
downward through the yielding débris which here overlies the mountain,
and in which we sometimes sank to the knees. Lower down we came once
more upon the ice. The glacier had at one place melted away from its
bounding cliff, which rose vertically to our right, while a wall of ice
60 or 80 feet high was on our left. Between the two was a narrow
passage, the floor of which was snow, which I knew to be hollow beneath:
my companion, however, was in advance of me, and he being the heavier
man, where he trod I followed without hesitation. On turning an angle of
the rock I noticed an expression of concern upon his countenance, and he
muttered audibly, "I did not expect this." The snow-floor had, in fact,
given way, and exposed to view a clear green lake, one boundary of which
was a sheer precipice of rock, and the other the aforesaid wall of ice;
the latter, however, curved a little at its base, so as to form a short
steep slope which overhung the water. My guide first tried the slope
alone; biting the ice with his shoe-nails, and holding on by the spike
of his bâton, he reached the other side. He then returned, and,
divesting myself of all superfluous clothes, as a preparation for the
plunge which I fully expected, I also passed in safety. Probably the
consciousness that I had water to fall into instead of pure space,
enabled me to get across without anxiety or mischance; but had I, like
my guide, been unable to swim, my feelings would have been far
different.
This accomplished, we went swiftly down the valley, and the more I saw
of my guide the more I liked him. He might, if he wished, have made his
day's journey shorter by stopping before he reached Graun, but he would
not do so. Every word he said to me regarding distances was true, and
there was not the slightest desire shown to magnify his own labour. I
learnt by mere accident that the day's work had cut up his feet, but his
cheerfulness and energy did not bate a jot till he had landed me in the
Black Eagle at Graun. Next morning he came to my room, and said that he
felt sufficiently refreshed to return home. I paid him what I owed him,
when he took my hand, and, silently bending down his head, kissed it;
then, standing erect, he stretched forth his right hand, which I grasped
firmly in mine, and bade him farewell; and thus I parted from Johann
Auer, my brave and truthful chamois-hunter.
On the following day I met Dr. Frankland in the Finstermuntz pass, and
that night we bivouacked together at Mals. Heavy rain fell throughout
the night, but it came from a region high above that of liquidity. It
was first snow, which, as it descended through the warmer strata of the
atmosphere, was reduced to water. Overhead, in the air, might be traced
a surface, below which the precipitate was liquid, above which it was
solid; and this surface, intersecting the mountains which surround Mals,
marked upon them a beautifully-defined _snow-line_, below which the
pines were dark and the pastures green, but above which pines and
pastures and crags were covered with the freshly-fallen snow.
[Sidenote: THE STELVIO. 1856.]
[Sidenote: COLOUR OF FRESH SNOW. 1856.]
On the 2nd of September we crossed the Stelvio. The brown cone of the
well-known Madatschspitze was clear, but the higher summits were
clouded, and the fragments of sunshine which reached the lower world
wandered like gleams of fluorescent light over the glaciers. Near the
snow-line the partial melting of the snow had rendered it coarsely
granular, but as we ascended it became finer, and the light emitted from
its cracks and cavities a pure and deep blue. When a staff was driven
into the snow low down the mountain, the colour of the light in the
orifice was scarcely sensibly blue, but higher up this increased in a
wonderful degree, and at the summit the effect was marvellous. I struck
my staff into the snow, and turned it round and round; the surrounding
snow cracked repeatedly, and flashes of blue light issued from the
fissures. The fragments of snow that adhered to the staff were, by
contrast, of a beautiful pink yellow, so that, on moving the staff with
such fragments attached to it up and down, it was difficult to resist
the impression that a pink flame was ascending and descending in the
hole. As we went down the other side of the pass, the effect became more
and more feeble, until, near the snow-line, it almost wholly
disappeared.
We remained that night at the baths of Bormio, but the following
afternoon being fine we wished to avail ourselves of the fair weather to
witness the scene from the summit of the pass. Twilight came on before
we reached Santa Maria, but a gorgeous orange overspread the western
horizon, from which we hoped to derive sufficient light. It was a little
too late when we reached the top, but still the scene was magnificent. A
multitude of mountains raised their crowns towards heaven, while above
all rose the snow-white cone of the Ortler. Far into the valley the
giant stretched his granite limbs, until they were hid from us by
darkness. As this deepened, the heavens became more and more crowded
with stars, which blazed like gems over the heads of the mountains. At
times the silence was perfect, unbroken save by the crackling of the
frozen snow beneath our own feet; while at other times a breeze would
swoop down upon us, keen and hostile, scattering the snow from the roofs
of the wooden galleries in frozen powder over us. Long after night had
set in, a ghastly gleam rested upon the summit of the Ortler, while the
peaks in front deepened to a dusky neutral tint, the more distant ones
being lost in gloom. We descended at a swift pace to Trafoi, which we
reached before 11 P.M.
[Sidenote: SINGULAR HAILSTORM. 1856.]
Meran was our next resting-place, whence we turned through the
Schnalzerthal to Unserfrau, and thence over the Hochjoch to Fend. From
a religious procession we took a guide, who, though partly intoxicated,
did his duty well. Before reaching the summit of the pass we were
assailed by a violent hailstorm, each hailstone being a frozen cone with
a rounded end. Had not their motion through the air something to do with
the shape of these hailstones? The theory of meteorites now generally
accepted is that they are small planetary bodies drawn to the earth by
gravity, and brought to incandescence by friction against the earth's
atmosphere. Such a body moving through the atmosphere must have
condensed hot air in front of it, and rarefied cool air behind it; and
the same is true to a small extent of a hailstone. This distribution of
temperature must, I imagine, have some influence on the shape of the
stone. Possibly also the stratified appearance of some hailstones may be
connected with this action.[A]
[Sidenote: THE HOCHJOCH AND FEND. 1856.]
The hail ceased and the heights above us cleared as we ascended. At the
top of the pass we found ourselves on the verge of a great _névé_, which
lay between two ranges of summits, sloping down to the base of each
range from a high and rounded centre: a wilder glacier scene I have
scarcely witnessed. Wishing to obtain a more perfect view of the region,
I diverged from the track followed by Dr. Frankland and the guide, and
climbed a ridge of snow about half a mile to the right of them. A
glorious expanse was before me, stretching itself in vast undulations,
and heaping itself here and there into mountainous cones, white and
pure, with the deep blue heaven behind them. Here I had my first
experience of hidden crevasses, and to my extreme astonishment once
found myself in the jaws of a fissure of whose existence I had not the
slightest notice. Such accidents have often occurred to me since, but
the impression made by the first is likely to remain the strongest. It
was dark when we reached the wretched Wirthshaus at Fend, where, badly
fed, badly lodged, and disturbed by the noise of innumerable rats, we
spent the night. Thus ended my brief glacier expedition of 1856; and on
the observations then made, and on subsequent experiments, was founded a
paper presented to the Royal Society by Mr. Huxley and myself.[B]
FOOTNOTES:
[A] I take the following account of a grander storm of the above
character from Hooker's 'Himalayan Journals,' vol. ii. p. 405.
"On the 20th (March, 1849) we had a change in the weather: a violent
storm from the south-west occurred at noon, with hail of a strange form,
the stones being sections of hollow spheres, half an inch across and
upwards, formed of cones with truncated apices and convex bases: these
cones were aggregated together with their bases outwards. The large
masses were followed by a shower of the separate conical pieces, and
that by heavy rain. On the mountains this storm was most severe: the
stones lay at Darjeeling for seven days, congealed into masses of ice
several feet long and a foot thick in sheltered places: at Purneah,
fifty miles south, stones one and two inches across fell, probably as
whole spheres."
[B] 'Phil. Trans.' 1857, pp. 327-346.--L. C. T.
[Sidenote: THE LAKE OF GENEVA. 1857.]
EXPEDITION OF 1857.
THE LAKE OF GENEVA.
(4.)
The time occupied in the observations of 1856 embraced about five whole
days; and though these days were laborious and instructive, still so
short a time proved to be wholly incommensurate with the claims of so
wide a problem. During the subsequent experimental treatment of the
subject, I had often occasion to feel the incompleteness of my
knowledge, and hence arose the desire to make a second expedition to the
Alps, for the purpose of expanding, fortifying, or, if necessary,
correcting first impressions.
On Thursday, the 9th of July, 1857, I found myself upon the Lake of
Geneva, proceeding towards Vevey. I had long wished to see the waters of
this renowned inland sea, the colour of which is perhaps more
interesting to the man of science than to the poets who have sung about
it. Long ago its depth of blue excited attention, but no systematic
examination of the subject has, so far as I know, been attempted. It may
be that the lake simply exhibits the colour of pure water. Ice is blue,
and it is reasonable to suppose that the liquid obtained from the fusion
of ice is of the same colour; but still the question presses--"Is the
blue of the Lake of Geneva to be entirely accounted for in this way?"
The attempts which have been made to explain it otherwise show that at
least a doubt exists as to the sufficiency of the above explanation.
[Sidenote: BLUENESS OF THE WATER. 1857.]
It is only in its deeper portions that the colour of the lake is
properly seen. Where the bottom comes into view the pure effect of the
water is disturbed; but where the water is deep the colour is deep:
between Rolle and Nyon for example, the blue is superb. Where the blue
was deepest, however, it gave me the impression of turbidity rather than
of deep transparency. At the upper portion of the lake the water through
which the steamer passed was of a blue green. Wishing to see the place
where the Rhone enters the lake, I walked on the morning of the 10th
from Villeneuve to Novelle, and thence through the woods to the river
side. Proceeding along an embankment, raised to defend the adjacent land
from the incursions of the river, an hour brought me to the place where
it empties itself into the lake. The contrast between the two waters was
very great: the river was almost white with the finely divided matter
which it held in suspension; while the lake at some distance was of a
deep ultramarine.
The lake in fact forms a reservoir where the particles held in
suspension by the river have time to subside, and its waters to become
pure. The subsidence of course takes place most copiously at the head of
the lake; and here the deposit continues to form new land, adding year
by year to the thousands of acres which it has already left behind it,
and invading more and more the space occupied by the water. Innumerable
plates of mica spangled the fine sand which the river brought down, and
these, mixing with the water, and flashing like minute mirrors as the
sun's rays fell upon them, gave the otherwise muddy stream a silvery
appearance. Had I an opportunity I would make the following
experiments:--
(_a_.) Compare the colour of the light transmitted by a column of the
lake water fifteen feet long with that transmitted by a second column,
of the same length, derived from the melting of freshly fallen mountain
snow.
(_b_.) Compare in the same manner the colour of the ordinary water of
the lake with that of the same water after careful distillation.
(_c_.) Strictly examine whether the light transmitted by the ordinary
water contains an excess of red over that transmitted by the distilled
water: this latter point, as will be seen farther on, is one of peculiar
interest.
The length is fixed at fifteen feet, because I have found this length
extremely efficient in similar experiments.
[Illustration: Fig. 3, 4. Boats' sails inverted by Atmospheric
Refraction.]
[Sidenote: ATMOSPHERIC REFRACTION. 1857.]
On returning to the pier at Villeneuve, a peculiar flickering motion was
manifest upon the surface of the distant portions of the lake, and I
soon noticed that the coast line was inverted by atmospheric refraction.
It required a long distance to produce the effect: no trace of it was
seen about the Castle of Chillon, but at Vevey and beyond it, the whole
coast was clearly inverted; and the houses on the margin of the lake
were also imaged to a certain height. Two boats at a considerable
distance presented the appearance sketched in Figs. 3 and 4; the hull of
each, except a small portion at the end, was invisible, but the sails
seemed lifted up high in the air, with their inverted images below; as
the boats drew nearer the hulls appeared inverted, the apparent height
of the vessel above the surface of the lake being thereby nearly
doubled, while the sails and higher objects, in these cases, were
almost completely cut away. When viewed through a telescope the sensible
horizon of the lake presented a billowy tumultuous appearance, fragments
being incessantly detached from it and suspended in the air.
[Sidenote: MIRAGE. 1857.]
The explanation of this effect is the same as that of the mirage of the
desert, which may be found in almost any book on physics, and which so
tantalized the French soldiers in Egypt. They often mistook this aërial
inversion for the reflection from a lake, and on trial found hot and
sterile sand at the place where they expected refreshing waters. The
effect was shown by Monge, one of the learned men who accompanied the
expedition, to be due to the total reflection of very oblique rays at
the upper surface of the layer of rarefied air which was nearest to the
heated earth. A sandy plain, in the early part of the day, is peculiarly
favourable for the production of such effects; and on the extensive flat
strand which stretches between Mont St. Michel and the coast adjacent to
Avranches in Normandy, I have noticed Mont Tombeline reflected as if
glass instead of sand surrounded it and formed its mirror.
[Sidenote: CHAMOUNI AND THE MONTANVERT. 1857.]
CHAMOUNI AND THE MONTANVERT.
(5.)
On the evening of the 12th of July I reached Chamouni; the weather was
not quite clear, but it was promising; white cumuli had floated round
Mont Blanc during the day, but these diminished more and more, and the
light of the setting sun was of that lingering rosy hue which bodes good
weather. Two parallel beams of a purple tinge were drawn by the shadows
of the adjacent peaks, straight across the Glacier des Bossons, and the
Glacier des Pèlerins was also steeped for a time in the same purple
light. Once when the surrounding red illumination was strong, the
shadows of the Grands Mulets falling upon the adjacent snow appeared of
a vivid green.
This green belonged to the class of _subjective_ colours, or colours
produced by contrast, about which a volume might be written. The eye
received the impression of green, but the colour was not external to the
eye. Place a red wafer on white paper, and look at it intently, it will
be surrounded in a little time by a green fringe: move the wafer bodily
away, and the entire space which it occupied upon the paper will appear
green. A body may have its proper colour entirely masked in this way.
Let a red wafer be attached to a piece of red glass, and from a
moderately illuminated position let the sky be regarded through the
glass; the wafer will appear of a vivid green. If a strong beam of light
be sent through a red glass and caused to fall upon a screen, which at
the same time is moderately illuminated by a separate source of white
light, an opaque body placed in the path of the beam will cast a green
shadow upon the screen which may be seen by several hundred persons at
once. If a blue glass be used, the shadow will be yellow, which is the
complementary colour to blue.
[Sidenote: COLOURED SHADOWS. 1857.]
When we suddenly pass from open sunlight to a moderately illuminated
room, it appears dark at first, but after a little time the eye regains
the power of seeing objects distinctly. Thus one effect of light upon
the eye is to render it less sensitive, and light of any particular
colour falling upon the eye blunts its appreciation of that colour. Let
us apply this to the shadow upon the screen. This shadow is moderately
illuminated by a jet of white light; but the space surrounding it is
red, the effect of which upon the eye is to blind it in some degree to
the perception of red. Hence, when the feeble white light of the shadow
reaches the eye, the red component of this light is, as it were,
abstracted from it, and the eye sees the residual colour, which is
green. A similar explanation applies to the shadows of the Grands
Mulets.
On the 13th of July I was joined by my friend Mr. Thomas Hirst, and on
the 14th we examined together the end of the Mer de Glace. In former
times the whole volume of the Arveiron escaped from beneath the ice at
the end of the glacier, forming a fine arch at its place of issue. This
year a fraction only of the water thus found egress; the greater portion
of it escaping laterally from the glacier at the summit of the rocks
called _Les Mottets_, down which it tumbled in a fine cascade. The vault
at the end of the glacier was nevertheless respectable, and rather
tempting to a traveller in search of information regarding the structure
of the ice. Perhaps, however, Nature meant to give me a friendly warning
at the outset, for, while speculating as to the wisdom of entering the
cavern, it suddenly gave way, and, with a crash which rivalled thunder,
the roof strewed itself in ruins upon the floor.
[Sidenote: SUNRISE AT CHAMOUNI. 1857.]
Many years ago I had read with delight Coleridge's poem entitled
'Sunrise in the Valley of Chamouni,' and to witness in all perfection
the scene described by the poet, I waited at Chamouni a day longer than
was otherwise necessary. On the morning of Wednesday, the 15th of July,
I rose before the sun; Mont Blanc and his wondrous staff of Aiguilles
were without a cloud; eastward the sky was of a pale orange which
gradually shaded off to a kind of rosy violet, and this again blended by
imperceptible degrees with the deep zenithal blue. The morning star was
still shining to the right, and the moon also turned a pale face towards
the rising day. The valley was full of music; from the adjacent woods
issued a gush of song, while the sound of the Arve formed a suitable
bass to the shriller melody of the birds. The mountain rose for a time
cold and grand, with no apparent stain upon his snows. Suddenly the
sunbeams struck his crown and converted it into a boss of gold. For some
time it remained the only gilded summit in view, holding communion with
the dawn while all the others waited in silence. These, in the order of
their heights, came afterwards, relaxing, as the sunbeams struck each in
succession, into a blush and smile.
[Sidenote: GLACIER DES BOIS. 1857.]
On the same day we had our luggage transported to the Montanvert, while
we clambered along the lateral moraine of the glacier to the Chapeau.
The rocks alongside the glacier were beautifully scratched and polished,
and I paid particular attention to them, for the purpose of furnishing
myself with a key to ancient glacier action. The scene to my right was
one of the most wonderful I had ever witnessed. Along the entire slope
of the Glacier des Bois, the ice was cleft and riven into the most
striking and fantastic forms. It had not yet suffered much from the
wasting influence of the summer weather, but its towers and minarets
sprang from the general mass with clean chiselled outlines. Some stood
erect, others leaned, while the white débris, strewn here and there over
the glacier, showed where the wintry edifices had fallen, breaking
themselves to pieces, and grinding the masses on which they fell to
powder. Some of them gave way during our inspection of the place, and
shook the valley with the reverberated noise of their fall. I
endeavoured to get near them, but failed; the chasms at the margin of
the glacier were too dangerous, and the stones resting upon the heights
too loosely poised to render persistence in the attempt excusable.
We subsequently crossed the glacier to the Montanvert, and I formally
took up my position there. The rooms of the hotel were separated from
each other by wooden partitions merely, and thus the noise of early
risers in one room was plainly heard in the next. For the sake of quiet,
therefore, I had my bed placed in the _château_ next door,--a little
octagonal building erected by some kind and sentimental Frenchman, and
dedicated "_à la Nature_." My host at first demurred, thinking the place
not "_propre_," but I insisted, and he acquiesced. True the stone floor
was dark with moisture, and on the walls a glistening was here and there
observable, which suggested rheumatism, and other penalties, but I had
had no experience of rheumatism, and trusted to the strength which
mountain air and exercise were sure to give me, for power to resist its
attacks. Moreover, to dispel some of the humidity, it was agreed that a
large pine fire should be made there on necessary occasions.
[Sidenote: QUARTERS AT THE MONTANVERT. 1857.]
Though singularly favoured on the whole, still our residence at the
Montanvert was sufficiently long to give us specimens of all kinds of
weather; and thus my château derived an interest from the mutations of
external nature. Sometimes no breath disturbed the perfect serenity of
the night, and the moon, set in a black-blue sky, turned a face of
almost supernatural brightness to the mountains, while in her absence
the thick-strewn stars alone flashed and twinkled through the
transparent air. Sometimes dull dank fog choked the valley, and heavy
rain plashed upon the stones outside. On two or three occasions we were
favoured by a thunderstorm, every peal of which broke into a hundred
echoes, while the seams of lightning which ran through the heavens
produced a wonderful intermittence of gloom and glare. And as I sat
within, musing on the experiences of the day, with my pine logs
crackling, and the ruddy fire-light gleaming over the walls, and lending
animation to the visages sketched upon them with charcoal by the guides,
I felt that my position was in every way worthy of a student of nature.
THE MER DE GLACE.
(6.)
[Sidenote: A RIVER OF ICE. 1857.]
The name "Mer de Glace" has doubtless led many who have never seen this
glacier to a totally erroneous conception of its character. Misled
probably by this term, a distinguished writer, for example, defines a
glacier to be a sheet of ice spread out upon the slope of a mountain;
whereas the Mer de Glace is indeed a _river_, and not a _sea_ of ice.
But certain forms upon its surface, often noticed and described, and
which I saw for the first time from the window of our hotel on the
morning of the 16th of July, suggest at once the origin of the name. The
glacier here has the appearance of a sea which, after it had been tossed
by a storm, had suddenly stiffened into rest. The ridges upon its
surface accurately resemble waves in shape, and this singular appearance
is produced in the following way:--
Some distance above the Montanvert--opposite to the Echelets--the
glacier, in passing down an incline, is rent by deep fissures, between
each two of which a ridge of ice intervenes. At first the edges of these
ridges are sharp and angular, but they are soon sculptured off by the
action of the sun. The bearing of the Mer de Glace being approximately
north and south, the sun at mid-day shines down the glacier, or rather
very obliquely across it; and the consequence is, that the fronts of the
ridges, which look downward, remain in shadow all the day, while the
backs of the ridges, which look up the glacier, meet the direct stroke
of the solar rays. The ridges thus acted upon have their hindmost angles
wasted off and converted into slopes which represent the _back_ of a
wave, while the opposite sides of the ridges, which are protected from
the sun, preserve their steepness, and represent the _front_ of the
wave. Fig. 5 will render my meaning at once plain.
[Sidenote: FROZEN WAVES. 1857.]
[Illustration: Fig. 5. Wave-like forms on the Mer de Glace.]
The dotted lines are intended to represent three of the ridges into
which the glacier is divided, with their interposed fissures; the dots
representing the boundaries of the ridges when the glacier is first
broken. The parallel shading lines represent the direction of the sun's
rays, which, falling obliquely upon the ridges, waste away the
right-hand corners, and finally produce wave-like forms.
We spent a day or two in making the general acquaintance of the glacier.
On the 16th we ascended till we came to the rim of the Talèfre basin,
from which we had a good view of the glacier system of the region. The
laminated structure of the ice was a point which particularly interested
me; and as I saw the exposed sections of the _névé_, counted the lines
of stratification, and compared these with the lines upon the ends of
the secondary glaciers, I felt the absolute necessity either of
connecting the veined _structure_ with the _strata_ by a continuous
chain of observations, or of proving by ocular evidence that they were
totally distinct from each other. I was well acquainted with the
literature of the subject, but nothing that I had read was sufficient to
prove what I required. Strictly speaking, nothing that had been written
upon the subject rose above the domain of _opinion_, while I felt that
without absolute _demonstration_ the question would never be set at
rest.
[Illustration: Fig. 6. Glacier Table.]
[Sidenote: GLACIER TABLES. 1857.]
On this day we saw some fine glacier tables; flat masses of rock, raised
high upon columns of ice: Fig. 6 is a sketch of one of the finest of
them. Some of them fell from their pedestals while we were near them,
and the clean ice-surfaces which they left behind sparkled with minute
stars as the small bubbles of air ruptured the film of water by which
they were overspread. I also noticed that "petit bruit de crépitation,"
to which M. Agassiz alludes, and which he refers to the rupture of the
ice by the expansion of the air-bubbles contained within it. When I
first read Agassiz's account of it, I thought it might be produced by
the rupture of the minute air-bubbles which incessantly escape from the
glacier. This, doubtless, produces an effect, but there is something in
the character of the sound to be referred, I think, to a less obvious
cause, which I shall notice further on.
[Sidenote: FIRST SIGHT OF THE DIRT-BANDS. 1857.]
At six P.M. this day I reached the Montanvert; and the same evening,
wrapping my plaid around me, I wandered up towards Charmoz, and from its
heights observed, as they had been observed fifteen years previously by
Professor Forbes, the _dirt-bands_ of the Mer de Glace. They were
different from any I had previously seen, and I felt a strong desire to
trace them to their origin. Content, however, with the performance of
the day, and feeling healthily tired by it, I lay down upon the bilberry
bushes and fell asleep. It was dark when I awoke, and I experienced some
difficulty and risk in getting down from the petty eminence referred to.
The illumination of the glacier, as remarked by Professor Forbes, has
great influence upon the appearance of the bands; they are best seen in
a subdued light, and I think for the following reasons:--
The dirt-bands are seen simply because they send less light to the eye
than the cleaner portions of the glacier which lie between them; two
surfaces, differently illuminated, are presented to the eye, and it is
found that this difference is more observable when the light is that of
evening than when it is that of noon.
It is only within certain limits that the eye is able to perceive
differences of intensity in different lights; beyond a certain
intensity, if I may use the expression, light ceases to be light, and
becomes mere pain. The naked eye can detect no difference in brightness
between the electric light and the lime light, although, when we come
to strict measurement, the former may possess many times the intensity
of the latter. It follows from this that we might reduce the ordinary
electric light to a fraction of its intensity, without any perceptible
change of brightness to the naked eye which looks at it. But if we
reduce the lime light in the same proportion the effect would be very
different. This light lies much nearer to the limit at which the eye can
appreciate differences of brightness, and its reduction might bring it
quite within this limit, and make it sensibly dimmer than before. Hence
we see that when two sources of intense light are presented to the eye,
by reducing both the lights in the same proportion, the _difference_
between them may become more perceptible.
[Sidenote: BANDS SEEN BEST BY TWILIGHT. 1857.]
Now the dirt-bands and the spaces between them resemble, in some
measure, the two lights above mentioned. By the full glare of noon both
are so strongly illuminated that the difference which the eye perceives
is very small; as the evening advances the light of both is lowered in
the same proportion, but the differential effect upon the eye is thereby
augmented, and the bands are consequently more clearly seen.
(7.)
On Friday, the 17th of July, we commenced our measurements. Through the
kindness of Sir Roderick Murchison, I found myself in the possession of
an excellent five-inch theodolite, an instrument with the use of which
both my friend Hirst and myself were perfectly familiar. We worked in
concert for a few days to familiarize our assistant with the mode of
proceeding, but afterwards it was my custom to simply determine the
position where a measurement was to be made, and to leave the execution
of it entirely to Mr. Hirst and our guide.
On the 20th of July I made a long excursion up the glacier, examining
the moraines, the crevasses, the structure, the moulins, and the
disintegration of the surface. I was accompanied by a boy named Edouard
Balmat,[A] and found him so good an iceman that I was induced to take
him with me on the following day also.
[Sidenote: THE CLEFT STATION. 1857.]
Looking upwards from the Montanvert to the left of the Aiguille de
Charmoz, a singular gap is observed in the rocky mountain wall, in the
centre of which stands a detached column of granite. Both cleft and
pillar are shown in the frontispiece, to the right. The eminence to the
left of this gap is signalised by Professor Forbes as one of the best
stations from which to view the Mer de Glace, and this point, which I
shall refer to hereafter as the _Cleft Station_, it was now my desire to
attain. From the Montanvert side a steep gully leads to the cleft; up
this couloir we proposed to try the ascent. At a considerable height
above the Mer de Glace, and closely hugging the base of the Aiguille de
Charmoz, is the small Glacier de Tendue, shown in the frontispiece, and
from which a steep slope stretches down to the Mer de Glace. This Tendue
is the most _talkative_ glacier I have ever known; the clatter of the
small stones which fall from it is incessant. Huge masses of granite
also frequently fall upon the glacier from the cliffs above it, and,
being slowly borne downwards by the moving ice, are at length seen
toppling above the terminal face of the glacier. The ice which supports
them being gradually melted, they are at length undermined, and sent
bounding down the slope with peal and rattle, according as the masses
among which they move are large or small. The space beneath the glacier
is cumbered with blocks thus sent down; some of them of enormous size.
[Sidenote: ROUGH ASCENT. 1857.]
The danger arising from this intermittent cannonade, though in reality
small, has caused the guides to swerve from the path which formerly led
across the slope to the promontory of Trélaporte. I say "small,"
because, even should a rock choose the precise moment at which a
traveller is passing to leap down, the boulders at hand are so large and
so capable of bearing a shock that the least presence of mind would be
sufficient to place him in safety. But presence of mind is not to be
calculated on under such circumstances, and hence the guides were right
to abandon the path.
Reaching the mouth of our gully after a rough ascent, we took to the
snow, instead of climbing the adjacent rocks. It was moist and soft, in
fact in a condition altogether favourable for the "regelation" of its
granules. As the foot pressed upon it the particles became cemented
together. A portion of the pressure was transmitted laterally, which
produced attachments beyond the boundary of the foot; thus as the latter
sank, it pressed upon a surface which became continually wider and more
rigid, and at length sufficiently strong to bear the entire weight of
the body; the pressed snow formed in fact a virtual _camel's foot_,
which soon placed a limit to the sinking. It is this same principle of
regelation which enables men to cross snow bridges in safety. By gentle
cautious pressure the loose granules of the substance are cemented into
a continuous mass, all sudden shocks which might cause the frozen
surfaces to snap asunder being avoided. In this way an arch of snow
fifteen or twenty inches in thickness may be rendered so firm that a
man will cross it, although it may span a chasm one hundred feet in
depth.
As we ascended, the incline became very steep, and once or twice we
diverged from the snow to the adjacent rocks; these were disintegrated,
and the slightest disturbance was sufficient to bring them down; some
fell, and from one of them I found it a little difficult to escape; for
it grazed my leg, inflicting a slight wound as it passed. Just before
reaching the cleft at which we aimed, the snow for a short distance was
exceedingly steep, but we surmounted it; and I sat for a time beside the
granite pillar, pleased to find that I could permit my legs to dangle
over a precipice without prejudice to my head.
[Sidenote: CHAMOIS ON THE MOUNTAINS. 1857.]
While we remained here a chamois made its appearance upon the rocks
above us. Deeming itself too near, it climbed higher, and then turned
round to watch us. It was soon joined by a second, and the two formed a
very pretty picture: their attitudes frequently changed, but they were
always graceful; with head erect and horns curved back, a light limb
thrown forward upon a ledge of rock, looking towards us with wild and
earnest gaze, each seemed a type of freedom and agility. Turning now to
the left, we attacked the granite tower, from which we purposed to scan
the glacier, and were soon upon its top. My companion was greatly
pleased--he was "très-content" to have reached the place--he felt
assured that many old guides would have retreated from that ugly gully,
with its shifting shingle and débris, and his elation reached its climax
in the declaration that, if I resolved to ascend Mont Blanc without a
guide, he was willing to accompany me.
[Sidenote: SCENE FROM THE STATION. 1857.]
From the position which we had attained, the prospect was exceedingly
fine, both of the glaciers and of the mountains. Beside us was the
Aiguille de Charmoz, piercing with its spikes of granite the clear air.
To my mind it is one of the finest of the Aiguilles, noble in mass, with
its summits singularly cleft and splintered. In some atmospheric
colourings it has the exact appearance of a mountain of cast copper, and
the manner in which some of its highest pinnacles are bent, suggesting
the idea of ductility, gives strength to the illusion that the mass is
metallic. At the opposite side of the glacier was the Aiguille Verte,
with a cloud poised upon its point: it has long been the ambition of
climbers to scale this peak, and on this day it was attempted by a young
French count with a long retinue of guides. He had not fair play, for
before we quitted our position we heard the rumble of thunder upon the
mountain, which indicated the presence of a foe more terrible than the
avalanches themselves. Higher to the right, and also at the opposite
side of the glacier, rose the Aiguille du Moine; and beyond was the
basin of the Talèfre, the ice cascade issuing from which appeared, from
our position, like the foam of a waterfall. Then came the Aiguille de
Léchaud, the Petite Jorasse, the Grande Jorasse, and the Mont Tacul; all
of which form a cradle for the Glacier de Léchaud. Mont Mallet, the
Périades, and the Aiguille Noire, came next, and then the singular
obelisk of the Aiguille du Géant, from which a serrated edge of cliff
descends to the summit of the "Col."
[Sidenote: SÉRACS OF THE COL DU GÉANT. 1857.]
Over the slopes of the Col du Géant was spread a coverlet of shining
snow, at some places apparently as smooth as polished marble, at others
broken so as to form precipices, on the pale blue faces of which the
horizontal lines of bedding were beautifully drawn. As the eye
approaches the line which stretches from the Rognon to the Aiguille
Noire, the repose of the _névé_ becomes more and more disturbed. Vast
chasms are formed, which however are still merely indicative of the
trouble in advance. If the glacier were lifted off we should probably
see that the line just referred to would lie along the summit of a
steep gorge; over this summit the glacier is pushed, and has its back
periodically broken, thus forming vast transverse ridges which follow
each other in succession down the slope. At the summit these ridges are
often cleft by fissures transverse to them, thus forming detached towers
of ice of the most picturesque and imposing character.[B] These towers
often fall; and while some are caught upon the platforms of the cascade,
others struggle with the slow energy of a behemoth through the débris
which opposes them, reach the edges of the precipices which rise in
succession along the fall, leap over, and, amid ice-smoke and
thunder-peals, fight their way downwards.
[Sidenote: GLACIER MOTION. 1857.]
A great number of secondary glaciers were in sight hanging on the steep
slopes of the mountains, and from them streams sped downwards, falling
over the rocks, and filling the valley with a low rich music. In front
of me, for example, was the Glacier du Moine, and I could not help
feeling as I looked at it, that the arguments drawn from the deportment
of such glaciers against the "sliding theory," and which are still
repeated in works upon the Alps, militate just as strongly against the
"viscous theory." "How," demands the antagonist of the sliding theory,
"can a secondary glacier exist upon so steep a slope? why does it not
slide down as an avalanche?" "But how," the person addressed may retort,
"can a mass which you assume to be viscous exist under similar
conditions? If it be viscous, what prevents it from rolling down?" The
sliding theory assumes the lubrication of the bed of the glacier, but on
this cold height the quantity melted is too small to lubricate the bed,
and hence the slow motion of these glaciers. Thus a sliding-theory man
might reason, and, if the external deportment of secondary glaciers were
to decide the question, De Saussure might perhaps have the best of the
argument.
And with regard to the current idea, originated by M. de Charpentier,
and adopted by Professor Forbes, that if a glacier slides it must slide
as an avalanche, it may be simply retorted that, in part, _it does so_;
but if it be asserted that an _accelerated motion_ is the necessary
motion of an avalanche, the statement needs qualification. An avalanche
on passing through a rough couloir soon attains a uniform velocity--its
motion being accelerated only up to the point when the sum of the
resistances acting upon it is equal to the force drawing it downwards.
These resistances are furnished by the numberless asperities which the
mass encounters, and which incessantly check its descent, and render an
accumulation of motion impossible. The motion of a man walking down
stairs may be on the whole uniform, but it is really made up of an
aggregate of small motions, each of which is accelerated; and it is easy
to conceive how a glacier moving over an uneven bed, when released from
one opposing obstacle will be checked by another, and its motion thus
rendered sensibly uniform.
[Sidenote: MORAINES. 1857.]
[Sidenote: TRIBUTARIES OF THE MER DE GLACE. 1857.]
[Illustration: Fig. 7. Tributaries of the Mer de Glace.]
From the Aiguille du Géant and Les Périades a glacier descended, which
was separated by the promontory of La Noire from the glacier proceeding
from the Col du Géant. A small moraine was formed between them, which is
marked _a_ upon the diagram, Fig. 7. The great mass of the glacier
descending from the Col du Géant came next, and this was bounded on the
side nearest to Trélaporte by a small moraine _b_, the origin of which I
could not see, its upper portion being shut out by a mountain
promontory. Between the moraine _b_ and the actual side of the valley
was another little glacier, derived from some of the lateral
tributaries. It was, however, between the moraines _a_ and _b_ that the
great mass of the Glacier du Géant really lay. At the promontory of the
Tacul the lateral moraines of the Glacier des Périades and of the
Glacier de Léchaud united to form the medial moraine _c_ of the Mer de
Glace. Carrying the eye across the Léchaud, we had the moraine _d_
formed by the union of the lateral moraines of the Léchaud and Talèfre;
further to the left was the moraine _e_, which came from the Jardin, and
beyond it was the second lateral moraine of the Talèfre. The Mer de
Glace is formed by the confluence of the whole of the glaciers here
named; being forced at Trélaporte through a passage, the width of which
appears considerably less than that of the single tributary, the Glacier
du Géant.
In the ice near Trélaporte the blue veins of the glacier are beautifully
shown; but they vary in distinctness according to the manner in which
they are looked at. When regarded obliquely their colour is not so
pronounced as when the vision plunges deeply into them. The weathered
ice of the surface near Trélaporte could be cloven with great facility;
I could with ease obtain plates of it a quarter of an inch thick, and
possessing two square feet of surface. On the 28th of July I followed
the veins several times from side to side across the Géant portion of
the Mer de Glace; starting from one side, and walking along the veins,
my route was directed obliquely downwards towards the axis of the
tributary. At the axis I was forced to turn, in order to keep along the
veins, and now ascended along a line which formed nearly the same angle
with the axis at the other side. Thus the veins led me as it were along
the two sides of a triangle, the vertex of which was near the centre of
the glacier. The vertex was, however, in reality rounded off, and the
figure rather resembled a hyperbola, which tended to coincidence with
its asymptotes. This observation corroborates those of Professor Forbes
with regard to the position of the veins, and, like him, I found that at
the centre the veining, whose normal direction would be transverse to
the glacier, was contorted and confused.
[Sidenote: WASTING OF ICE. 1857.]
Near the side of the Glacier du Géant, above the promontory of
Trélaporte, the ice is rent in a remarkable manner. Looking upwards from
the lower portions of the glacier, a series of vertical walls, rising
apparently one above the other, face the observer. I clambered up among
these singular terraces, and now recognise, both from my sketch and
memory, that their peculiar forms are due to the same action as that
which has given their shape to the "billows" of the Mer de Glace. A
series of profound crevasses is first formed. The Glacier du Géant
deviates 14° from the meridian line, and hence the sun shines nearly
down it during the middle portion of each day. The backs of the ridges
between the crevasses are thus rounded off, one boundary of each fissure
is destroyed, or at least becomes a mere steep declivity, while the
other boundary being shaded from the sun preserves its verticality; and
thus a very curious series of precipices is formed.
Through all this dislocation, the little moraine on which I have placed
the letter _b_ in the sketch maintains its right to existence, and under
it the laminated structure of this portion of the glacier appears to
reach its most perfect development. The moraine was generally a mere
dirt track, but one or two immense blocks of granite were perched upon
it. I examined the ice underneath one of these, being desirous of seeing
whether the pressure resulting from its enormous weight would produce a
veining, but the result was not satisfactory. Veins were certainly to be
seen in directions different from the normal ones, but whether they were
due to the bending of the latter, or were directly owing to the pressure
of the block, I could not say. The sides of a stream which had cut a
deep gorge in the clean ice of the Glacier du Géant afforded a fine
opportunity of observing the structure. It was very remarkable--highly
significant indeed in a theoretic point of view. Two long and
remarkably deep blue veins traversed the bottom of the stream, and
bending upwards at a place where the rivulet curved, drew themselves
like a pair of parallel lines upon the clean white ice. But the general
structure was of a totally different character; it did not consist of
long bars, but approximated to the lenticular form, and was, moreover,
of a washy paleness, which scarcely exceeded in depth of colouring the
whitish ice around.
[Sidenote: GROOVES ON THE SURFACE. 1857.]
To the investigator of the structure nothing can be finer than the
appearance of the glacier from one of the ice terraces cut in the
Glacier du Géant by its passage round Trélaporte. As far as the vision
extended the dirt upon the surface of the ice was arranged in striæ.
These striæ were not always straight lines, nor were they unbroken
curves. Within slight limits the various parts into which a glacier is
cut up by its crevasses enjoy a kind of independent motion. The grooves,
for example, on two ridges which have been separated by a small fissure,
may one day have their striæ perfect continuations of each other, but in
a short time this identity of direction may be destroyed by a difference
of motion between the ridges. Thus it is that the grooves upon the
surface above Trélaporte are bent hither and thither, a crack or seam
always marking the point where their continuity is ruptured. This
bending occurs, however, within limits sufficiently small to enable the
striæ to preserve the same general direction.
[Sidenote: SEAMS OF WHITE ICE. 1857.]
My attention had often been attracted this day by projecting masses of
what at first appeared to be pure white snow, rising in seams above the
general surface of the glacier. On examination, however, I found them to
be compact ice, filled with innumerable air-cells, and so resistant as
to maintain itself in some places at a height of four feet above the
general level. When amongst the ridges they appeared discontinuous and
confused, being scattered apparently at random over the glacier; but
when viewed from a sufficient distance, the detached parts showed
themselves to belong to a system of white seams which swept quite across
the Glacier du Géant, in a direction concentric with the structure.
Unable to account for these singular seams, I climbed up among the
tributary glaciers on the Rognon side of the Glacier du Géant, and
remained there until the sun sank behind the neighbouring peaks, and the
fading light warned me that it was time to return.
FOOTNOTES:
[A] "Le petit Balmat" my host always called him.
[B] To such towers the name _Séracs_ is applied. In the chalets of
Savoy, after the richer curd has been precipitated by rennet, a stronger
acid is used to throw down what remains; an inferior kind of cheese
called _Sérac_ is thus formed, the shape and colour of which have
suggested the application of the term to the cubical masses of ice.
(8.)
Early on the following day I was again upon the ice. I first confined
myself to the right side of the Glacier du Géant, and found that the
veins of white ice which I had noticed on the previous day were
exclusively confined to this glacier, or to the space between the
moraines _a_ and _b_ (Fig. 7), bending up so that the moraine _a_
between the Glacier du Géant and the Glacier des Périades was tangent to
them. At a good distance up the glacier I encountered a considerable
stream rushing across it almost from side to side. I followed the
rivulet, examining the sections which it exposed. At a certain point
three other streams united, and formed at their place of confluence a
small green lake. From this a rivulet rushed, which was joined by the
stream whose track I had pursued, and at this place of junction a second
green lake was formed, from which flowed a stream equal in volume to the
sum of all the tributaries. It entered a crevasse, and took the bottom
of the fissure for its bed. Standing at the entrance of the chasm, a low
muffled thunder resounding through the valley attracted my attention. I
followed the crevasse, which deepened and narrowed, and, by the blue
light of the ice, could see the stream gambolling along its bottom, and
flashing as it jumped over the ledges which it encountered in its way.
The fissure at length came to an end: placing a foot on each side of it,
and withholding the stronger light from my eyes, I looked down between
its shining walls, and saw the stream plunge into a shaft which carried
it to the bottom of the glacier.
Slowly, and in zigzag fashion, as the crevasses demanded, I continued to
ascend, sometimes climbing vast humps of ice from which good views of
the surrounding glacier were obtained; sometimes hidden in the hollows
between the humps, in which also green glacier tarns were often formed,
very lonely and very beautiful.
[Sidenote: A LAKE SET FREE. 1857.]
While standing beside one of these, and watching the moving clouds which
it faithfully mirrored, I heard the sound of what appeared to be a
descending avalanche, but the time of its continuance surprised me.
Looking through my opera-glass in the direction of the sound, I saw
issuing from the end of a secondary glacier on the Tacul side a torrent
of what appeared to me to be stones and mud. I could see the stones and
finer débris jumping down the declivities, and shaping themselves into
singular cascades. The noise continued for a quarter of an hour, after
which the torrent rapidly diminished, until, at length, the ordinary
little stream due to the melting of the glacier alone remained. A
subglacial lake had burst its boundary, and carried along with it in its
rush downwards the débris which it met with in its course.
[Sidenote: IMPRESSIVE SCENE. 1857.]
In some places I found the crevasses difficult, the ice being split in a
very singular manner. Vast plates of it not more than a foot in
thickness were sometimes detached from the sides of the crevasses, and
stood alone. I was now approaching the base of the _séracs_, and the
glacier around me still retained a portion of the turbulence of the
cascade. I halted at times amid the ruin and confusion, and examined
with my glass the cascade itself. It was a wild and wonderful scene,
suggesting throes of spasmodic energy, though, in reality, all its
dislocation had been _slowly_ and _gradually_ produced. True, the
stratified blocks which here and there cumbered the terraces suggested
_débacles_, but these were local and partial, and did not affect
the general question. There is scarcely a case of geological
disturbance which could not be matched with its analogue upon the
glaciers,--contortions, faults, fissures, joints, and dislocations,--but
in the case of the ice we can prove the effects to be due to
slowly-acting causes; how reasonable is it then to ascribe to the
operation of similar causes, which have had an incomparably longer time
to work, many geological effects which at first sight might suggest
sudden convulsion!
Wandering slowly upwards, successive points of attraction drawing me
almost unconsciously on, I found myself as the day was declining deep in
the entanglements of the ice. A shower commenced, and a splendid rainbow
threw an oblique arch across the glacier. I was quite alone; the scene
was exceedingly impressive, and the possibility of difficulties on which
I had not calculated intervening between me and the lower glacier, gave
a tinge of anxiety to my position. I turned towards home; crossed some
bosses of ice and rounded others; I followed the tracks of streams which
were very irregular on this portion of the glacier, bending hither and
thither, rushing through deep-cut channels, falling in cascades and
expanding here and there to deep green lakes; they often plunged into
the depths of the ice, flowed under it with hollow gurgle, and
reappeared at some distant point. I threaded my way cautiously amid
systems of crevasses, scattering with my axe, to secure a footing, the
rotten ice of the sharper crests, which fell with a ringing sound into
the chasms at either side. Strange subglacial noises were sometimes
heard, as if caverns existed underneath, into which blocks of ice fell
at intervals, transmitting the shock of their fall with a dull boom to
the surface of the glacier. By the steady surmounting of difficulties
one after another, I at length placed them all behind me, and afterwards
hastened swiftly along the glacier to my mountain home.
[Sidenote: CHAMOUNI RULES. 1857.]
On the 30th incessant rain confined us to indoor work; on the 31st we
determined the velocity with which the glacier is forced through the
entrance of the trunk valley at Trélaporte, and also the motion of the
Grand Moulin. We also determined both the velocity and the width of the
Glacier du Géant. The 1st of August was spent by me at the cascade of
the Talèfre, examining the structure, crumpling, and scaling off of the
ice. Finding that the rules at Chamouni put an unpleasant limit to my
demands on my guide Simond, I visited the Guide Chef on the 2nd of
August, and explained to him the object of my expedition, pointing out
the inconvenience which a rigid application of the rules made for
tourists would impose upon me. He had then the good sense to acknowledge
the reasonableness of my remarks, and to grant me the liberty I
requested. The 3rd of August was employed in determining the velocity
and width of the Glacier de Léchaud, and in observations on the
lamination of the glacier.
[Sidenote: THE JARDIN. 1857.]
THE JARDIN.
(9.)
[Sidenote: A RESERVOIR OF ICE. 1857.]
On the 4th of August, with a view of commencing a series of observations
on the inclinations of the Mer de Glace and its tributaries, we had our
theodolite transported to the _Jardin_, which, as is well known, lies
like an island in the middle of the Glacier du Talèfre. We reached the
place by the usual route, and found some tourists reposing on the soft
green sward which covers the lower portion, and to which, and the
flowers which spangle it, the place owes its name. Towards the summit of
the Jardin, a rock jutted forward, apparently the very apex of the
place, or at least hiding by its prominence everything that might exist
behind it; leaving our guide with the instrument, we aimed at this, and
soon left the grass and flowers behind us. Stepping amid broken
fragments of rock, along slopes of granite, with fat felspar crystals
which gave the boots a hold, and crossing at intervals patches of snow,
which continued still to challenge the summer heat, I at length found
myself upon the peak referred to; and, although it was not the highest,
the unimpeded view which it commanded induced me to get astride it. The
Jardin was completely encircled by the ice of the glacier, and this was
held in a mountain basin, which was bounded all round by a grand and
cliffy rim. The outline of the dark brown crags--a deeply serrated and
irregular line--was forcibly drawn against the blue heaven, and still
more strongly against some white and fleecy clouds which lay here and
there behind it; while detached spears and pillars of rock, sculptured
by frost and lightning, stood like a kind of defaced statuary along the
ridge. All round the basin the snow reared itself like a buttress
against the precipitous cliffs, being streaked and fluted by the descent
of blocks from the summits. This mighty tub is the collector of one of
the tributaries of the Mer de Glace. According to Professor Forbes, its
greatest diameter is 4200 yards, and out of it the half-formed ice is
squeezed through a precipitous gorge about 700 yards wide, forming there
the ice cascade of the Talèfre. Bounded on one side by the Grande
Jorasse, and on the other by Mont Mallet, the principal tributary of the
Glacier de Léchaud lay white and pure upon the mountain slope. Round
further to the right we had the vast plateau whence the Glacier du Géant
is fed, fenced on the left by the Aiguille du Géant and the Aiguille
Noire, and on the right by the Monts Maudits and Mont Blanc. The scene
was a truly majestic one. The mighty Aiguilles piercing the sea of air,
the soft white clouds floating here and there behind them; the shining
snow with its striped faults and precipices; the deep blue firmament
overhead; the peals of avalanches and the sound of water;--all conspired
to render the scene glorious, and our enjoyment of it deep.
A voice from above hailed me as I moved from my perch; it was my friend,
who had found a lodgment upon the edge of a rock which was quite
detached from the Jardin, being the first to lift its head in opposition
to the descending _névé_. Making a détour round a steep concave slope of
the glacier, I reached the flat summit of the rock. The end of a ridge
of ice abutted against it, which was split and bent by the pressure so
as to form a kind of arch. I cut steps in the ice, and ascended until I
got beneath the azure roof. Innumerable little rills of pellucid water
descended from it. Some came straight down, clear for a time, and
apparently motionless, rapidly tapering at first, and more slowly
afterwards, until, at the point of maximum contraction, they resolved
themselves into strings of liquid pearls which pattered against the ice
floor underneath. Others again, owing to the directions of the little
streamlets of which they were constituted, formed spiral figures of
great beauty: one liquid vein wound itself round another, forming a
spiral protuberance, and owing to the centrifugal motion thus imparted,
the vein, at its place of rupture, scattered itself laterally in little
liquid spherules.[A] Even at this great elevation the structure of the
ice was fairly developed, not with the sharpness to be observed lower
down, but still perfectly decided. Blue bands crossed the ridge of ice
to which I have referred, at right angles to the direction of the
pressure.
[Sidenote: MORAINES OF THE TALÈFRE. 1857.]
I descended, and found my friend beneath an overhanging rock.
Immediately afterwards a peal like that of thunder shook the air, and
right in front of us an avalanche darted down the brown cliffs, then
along a steep slope of snow which reared itself against the mountain
wall, carrying with it the débris of the rocks over which it passed,
until it finally lay a mass of sullied rubbish at the base of the
incline: the whole surface of the Talèfre is thus soiled. Another peal
was heard immediately afterwards, but the avalanche which caused it was
hidden from us by a rocky promontory. From this same promontory the
greater portion of the medial moraine which descends the cascade of the
Talèfre is derived, forming at first a gracefully winding curve, and
afterwards stretching straight to the summit of the fall. In the chasms
of the cascade its boulders are engulfed, but the lost moraine is
restored below the fall, as if disgorged by the ice which had swallowed
it. From the extremity of the Jardin itself a mere driblet of a moraine
proceeds, running parallel to the former, and like it disappearing at
the summit of the cascade.
[Sidenote: AMONG THE CREVASSES. 1857.]
We afterwards descended towards the cascade, but long before this is
attained the most experienced iceman would find himself in difficulty.
Transverse crevasses are formed, which follow each other so speedily as
to leave between them mere narrow ridges of ice, along which we moved
cautiously, jumping the adjacent fissures, or getting round them, as the
case demanded. As we approached the jaws of the gorge, the ridges
dwindled to mere plates and wedges, which being bent and broken by the
lateral pressure, added to the confusion, and warned us not to advance.
The position was in some measure an exciting one. Our guide had never
been here before; we were far from the beaten track, and the riven
glacier wore an aspect of treacherous hostility. As at the base of the
_séracs_, a subterranean noise sometimes announced the falling of
ice-blocks into hollows underneath, the existence of which the resonant
concussion of the fallen mass alone revealed. There was thus a dash of
awe mingled with our thoughts; a stirring up of the feelings which
troubled the coolness of the intellect. We finally swerved to the right,
and by a process the reverse of straightforward reached the Couvercle.
Nightfall found us at the threshold of our hotel.
FOOTNOTES:
[A] The recent hydraulic researches of Professor Magnus furnish some
beautiful illustrations of this action.
(10.)
[Sidenote: ROUND HAILSTONES. 1857.]
[Sidenote: A DANGEROUS LEAP. 1857.]
On the 5th we were engaged for some time in an important measurement at
the Tacul. We afterwards ascended towards the _séracs_, and determined
the inclinations of the Glacier du Géant downwards. Dense cloud-masses
gathered round the points of the Aiguilles, and the thunder bellowed at
intervals from the summit of Mont Blanc. As we descended the Mer de
Glace the valley in front of us was filled with a cloud of pitchy
darkness. Suddenly from side to side this field of gloom was riven by a
bar of lightning of intolerable splendour; it was followed by a peal of
commensurate grandeur, the echoes of which leaped from cliff to cliff
long after the first sound had died away. The discharge seemed to unlock
the clouds above us, for they showered their liquid spheres down upon us
with a momentum like that of swan-shot: all the way home we were
battered by this pellet-like rain. On the 6th the rain continued with
scarcely any pause; on the 7th I was engaged all day upon the Glacier du
Géant; on the morning of the 8th heavy hail had fallen there, the stones
being perfect spheres; the rounded rain-drops had solidified during
their descent without sensible change of form. When this hail was
squeezed together, it exactly resembled a mass of oolitic limestone
which I had picked up in 1853 near Blankenburg in the Hartz. Mr. Hirst
and myself were engaged together this day taking the inclinations: he
struck his theodolite at the Angle, and went home accompanied by Simond,
and the evening being extremely serene, I pursued my way down the centre
of the glacier towards the Echelets. The crevasses as I advanced became
more deep and frequent, the ridges of ice between them becoming
gradually narrower. They were very fine, their downward faces being
clear cut, perfectly vertical, and in many cases beautifully veined.
Vast plates of ice moreover often stood out midway between the walls of
the chasms, as if cloven from the glacier and afterwards set on edge.
The place was certainly one calculated to test the skill and nerve of an
iceman; and as the day drooped, and the shadow in the valley deepened, a
feeling approaching to awe took possession of me. My route was an
exaggerated zigzag; right and left amid the chasms wherever a hope of
progress opened; and here I made the experience which I have often
repeated since, and laid to heart as regards intellectual work also,
that enormous difficulties may be overcome when they are attacked in
earnest. Sometimes I found myself so hedged in by fissures that escape
seemed absolutely impossible; but close and resolute examination so
often revealed a means of exit, that I felt in all its force the brave
verity of the remark of Mirabeau, that the word "impossible" is a mere
blockhead of a word. It finally became necessary to reach the shore, but
I found this a work of extreme difficulty. At length, however, it became
pretty evident that, if I could cross a certain crevasse, my retreat
would be secured. The width of the fissure seemed to be fairly within
jumping distance, and if I could have calculated on a safe purchase for
my foot I should have thought little of the spring; but the ice on the
edge from which I was to leap was loose and insecure, and hence a kind
of nervous thrill shot through me as I made the bound. The opposite side
was fairly reached, but an involuntary tremor shook me all over after I
felt myself secure. I reached the edge of the glacier without further
serious difficulty, and soon after found myself steeped in the creature
comforts of our hotel.
On Monday, August 10th, I had the great pleasure of being joined by my
friend Huxley; and though the weather was very unpromising, we started
together up the glacier, he being desirous to learn something of its
general features, and, if possible, to reach the Jardin. We reached the
Couvercle, and squeezed ourselves through the Egralets; but here the
rain whizzed past us, and dense fog settled upon the cascade of the
Talèfre, obscuring all its parts. We met Mr. Galton, the African
traveller, returning from an attempt upon the Jardin; and learning that
his guides had lost their way in the fog, we deemed it prudent to
return.
The foregoing brief notes will have informed the reader that at the
period of Mr. Huxley's arrival I was not without due training upon the
ice; I may also remark, that on the 25th of July I reached the summit
of the Col du Géant, accompanied by the boy Balmat, and returned to the
Montanvert on the same day. My health was perfect, and incessant
practice had taught me the art of dealing with the difficulties of the
ice. From the time of my arrival at the Montanvert the thought of
ascending Mont Blanc, and thus expanding my knowledge of the glaciers,
had often occurred to me, and I think I was justified in feeling that
the discipline which both my friend Hirst and myself had undergone ought
to enable us to accomplish the journey in a much more modest way than
ordinary. I thought a single guide sufficient for this purpose, and I
was strengthened in this opinion by the fact that Simond, who was a man
of the strictest prudence, and who at first declared four guides to be
necessary, had lowered his demand first to two, and was now evidently
willing to try the ascent with us alone.
[Sidenote: PREPARATIONS FOR A CLIMB. 1857.]
On mentioning the thing to Mr. Huxley he at once resolved to accompany
us. On the 11th of August the weather was exceedingly fine, though the
snow which had fallen during the previous days lay thick upon the
glacier. At noon we were all together at the Tacul, and the subject of
attempting Mont Blanc was mooted and discussed. My opinion was that it
would be better to wait until the fresh snow which loaded the mountain
had disappeared; but the weather was so exquisite that my friends
thought it best to take advantage of it. We accordingly entered into an
agreement with our guide, and immediately descended to make preparations
for commencing the expedition on the following morning.
FIRST ASCENT OF MONT BLANC, 1857.
(11.)
[Sidenote: SCENE FROM THE CHARMOZ. 1857.]
On Wednesday, the 12th of August, we rose early, after a very brief rest
on my part. Simond had proposed to go down to Chamouni, and commence the
ascent in the usual way, but we preferred crossing the mountains from
the Montanvert, straight to the Glacier des Bossons. At eight o'clock we
started, accompanied by two porters who were to carry our provisions to
the Grands Mulets. Slowly and silently we climbed the hill-side towards
Charmoz. We soon passed the limits of grass and rhododendrons, and
reached the slabs of gneiss which overspread the summit of the ridge,
lying one upon the other like coin upon the table of a money-changer.
From the highest-point I turned to have a last look at the Mer de Glace;
and through a pair of very dark spectacles I could see with perfect
distinctness the looped dirt-bands of the glacier, which to the naked
eye are scarcely discernible except by twilight. Flanking our track to
the left rose a series of mighty Aiguilles--the Aiguille de Charmoz,
with its bent and rifted pinnacles; the Aiguille du Grépon, the Aiguille
de Blaitière, the Aiguille du Midi, all piercing the heavens with their
sharp pyramidal summits. Far in front of us rose the grand snow-cone of
the Dôme du Goûter, while, through a forest of dark pines which gathered
like a cloud at the foot of the mountain, gleamed the white minarets of
the Glacier des Bossons. Below us lay the Valley of Chamouni, beyond
which were the Brévent and the chain of the Aiguilles Rouges; behind us
was the granite obelisk of the Aiguille du Dru, while close at hand
science found a corporeal form in a pyramid of stones used as a
trigonometrical station by Professor Forbes. Sound is known to travel
better up hill than down, because the pulses transmitted from a denser
medium to a rarer, suffer less loss of intensity than when the
transmission is in the opposite direction; and now the mellow voice of
the Arve came swinging upwards from the heavier air of the valley to the
lighter air of the hills in rich deep cadences.
[Sidenote: PASSAGE TO THE PIERRE À L'ECHELLE. 1857.]
The way for a time was excessively rough, our route being overspread
with the fragments of peaks which had once reared themselves to our
left, but which frost and lightning had shaken to pieces, and poured in
granite avalanches down the mountain. We were sometimes among huge
angular boulders, and sometimes amid lighter shingle, which gave way at
every step, thus forcing us to shift our footing incessantly. Escaping
from these, we crossed the succession of secondary glaciers which lie at
the feet of the Aiguilles, and having secured firewood found ourselves
after some hours of hard work at the Pierre à l'Echelle. Here we were
furnished with leggings of coarse woollen cloth to keep out the snow;
they were tied under the knees and quite tightly again over the insteps,
so that the legs were effectually protected. We had some refreshment,
possessed ourselves of the ladder, and entered upon the glacier.
[Sidenote: LADDER LEFT BEHIND. 1857.]
[Sidenote: DIFFICULT CREVASSES. 1857.]
The ice was excessively fissured: we crossed crevasses and crept round
slippery ridges, cutting steps in the ice wherever climbing was
necessary. This rendered our progress very slow. Once, with the
intention of lending a helping hand, I stepped forward upon a block of
granite which happened to be poised like a rocking stone upon the ice,
though I did not know it; it treacherously turned under me; I fell, but
my hands were in instant requisition, and I escaped with a bruise, from
which, however, the blood oozed angrily. We found the ladder necessary
in crossing some of the chasms, the iron spikes at its end being firmly
driven into the ice at one side, while the other end rested on the
opposite side of the fissure. The middle portion of the glacier was not
difficult. Mounds of ice rose beside us right and left, which were
sometimes split into high towers and gaunt-looking pyramids, while the
space between was unbroken. Twenty minutes' walking brought us again to
a fissured portion of the glacier, and here our porter left the ladder
on the ice behind him. For some time I was not aware of this, but we
were soon fronted by a chasm to pass which we were in consequence
compelled to make a long and dangerous circuit amid crests of crumbling
ice. This accomplished, we hoped that no repetition of the process would
occur, but we speedily came to a second fissure, where it was necessary
to step from a projecting end of ice to a mass of soft snow which
overhung the opposite side. Simond could reach this snow with his
long-handled axe; he beat it down to give it rigidity, but it was
exceedingly tender, and as he worked at it he continued to express his
fears that it would not bear us. I was the lightest of the party, and
therefore tested the passage, first; being partially lifted by Simond on
the end of his axe, I crossed the fissure, obtained some anchorage at
the other side, and helped the others over. We afterwards ascended until
another chasm, deeper and wider than any we had hitherto encountered,
arrested us. We walked alongside of it in search of a snow bridge, which
we at length found, but the keystone of the arch had unfortunately given
way, leaving projecting eaves of snow at both sides, between which we
could look into the gulf, till the gloom of its deeper portions cut the
vision short. Both sides of the crevasse were sounded, but no sure
footing was obtained; the snow was beaten and carefully trodden down as
near to the edge as possible, but it finally broke away from the foot
and fell into the chasm. One of our porters was short-legged and a bad
iceman; the other was a daring fellow, and he now threw the knapsack
from his shoulders, came to the edge of the crevasse, looked into it,
but drew back again. After a pause he repeated the act, testing the snow
with his feet and staff. I looked at the man as he stood beside the
chasm manifestly undecided as to whether he should take the step upon
which his life would hang, and thought it advisable to put a stop to
such perilous play. I accordingly interposed, the man withdrew from the
crevasse, and he and Simond descended to fetch the ladder. While they
were away Huxley sat down upon the ice, with an expression of fatigue
stamped upon his countenance: the spirit and the muscles were evidently
at war, and the resolute will mixed itself strangely with the sense of
peril and feeling of exhaustion. He had been only two days with us, and,
though his strength is great, he had had no opportunity of hardening
himself by previous exercise upon the ice for the task which he had
undertaken. The ladder now arrived, and we crossed the crevasse. I was
intentionally the last of the party, Huxley being immediately in front
of me. The determination of the man disguised his real condition from
everybody but myself, but I saw that the exhausting journey over the
boulders and débris had been too much for his London limbs. Converting
my waterproof haversack into a cushion, I made him sit down upon it at
intervals, and by thus breaking the steep ascent into short stages we
reached the cabin of the Grands Mulets together. Here I spread a rug on
the boards, and placing my bag for a pillow, he lay down, and after an
hour's profound sleep he rose refreshed and well; but still he thought
it wise not to attempt the ascent farther. Our porters left us: a bâton
was stretched across the room over the stove, and our wet socks and
leggings were thrown across it to dry; our boots were placed around the
fire, and we set about preparing our evening meal. A pan was placed upon
the fire, and filled with snow, which in due time melted and boiled; I
ground some chocolate and placed it in the pan, and afterwards ladled
the beverage into the vessels we possessed, which consisted of two
earthen dishes and the metal cases of our brandy flasks. After supper
Simond went out to inspect the glacier, and was observed by Huxley, as
twilight fell, in a state of deep contemplation beside a crevasse.
[Sidenote: STAR TWINKLING. 1857.]
Gradually the stars appeared, but as yet no moon. Before lying down we
went out to look at the firmament, and noticed, what I suppose has been
observed to some extent by everybody, that the stars near the horizon
twinkled busily, while those near the zenith shone with a steady light.
One large star in particular excited our admiration; it flashed
intensely, and changed colour incessantly, sometimes blushing like a
ruby, and again gleaming like an emerald. A determinate colour would
sometimes remain constant for a sensible time, but usually the flashes
followed each other in very quick succession. Three planks were now
placed across the room near the stove, and upon these, with their rugs
folded round them, Huxley and Hirst stretched themselves, while I
nestled on the boards at the most distant end of the room. We rose at
eleven o'clock, renewed the fire and warmed ourselves, after which we
lay down again. I at length observed a patch of pale light upon the
wooden wall of the cabin, which had entered through a hole in the end of
the edifice, and rising found that it was past one o'clock. The
cloudless moon was shining over the wastes of snow, and the scene
outside was at once wild, grand, and beautiful.
[Sidenote: START FROM THE GRANDS MULETS. 1857.]
Breakfast was soon prepared, though not without difficulty; we had no
candles, they had been forgotten; but I fortunately possessed a box of
wax matches, of which Huxley took charge, patiently igniting them in
succession, and thus giving us a tolerably continuous light. We had
some tea, which had been made at the Montanvert, and carried to the
Grands Mulets in a bottle. My memory of that tea is not pleasant; it had
been left a whole night in contact with its leaves, and smacked strongly
of tannin. The snow-water, moreover, with which we diluted it was not
pure, but left a black residuum at the bottom of the dishes in which the
beverage was served. The few provisions deemed necessary being placed in
Simond's knapsack, at twenty minutes past two o'clock we scrambled down
the rocks, leaving Huxley behind us.
The snow was hardened by the night's frost, and we were cheered by the
hope of being able to accomplish the ascent with comparatively little
labour. We were environed by an atmosphere of perfect purity; the larger
stars hung like gems above us, and the moon, about half full, shone with
wondrous radiance in the dark firmament. One star in particular, which
lay eastward from the moon, suddenly made its appearance above one of
the Aiguilles, and burned there with unspeakable splendour. We turned
once towards the Mulets, and saw Huxley's form projected against the sky
as he stood upon a pinnacle of rock; he gave us a last wave of the hand
and descended, while we receded from him into the solitudes.
The evening previous our guide had examined the glacier for some
distance, his progress having been arrested by a crevasse. Beside this
we soon halted: it was spanned at one place by a bridge of snow, which
was of too light a structure to permit of Simond's testing it alone; we
therefore paused while our guide uncoiled a rope and tied us all
together. The moment was to me a peculiarly solemn one. Our little party
seemed so lonely and so small amid the silence and the vastness of the
surrounding scene. We were about to try our strength under unknown
conditions, and as the various possibilities of the enterprise crowded
on the imagination, a sense of responsibility for a moment oppressed
me. But as I looked aloft and saw the glory of the heavens, my heart
lightened, and I remarked cheerily to Hirst that Nature seemed to smile
upon our work. "Yes," he replied, in a calm and earnest voice, "and, God
willing, we shall accomplish it."
[Sidenote: A WRONG TURN. 1857.]
A pale light now overspread the eastern sky, which increased, as we
ascended, to a daffodil tinge; this afterwards heightened to orange,
deepening at one extremity into red, and fading at the other into a pure
ethereal hue to which it would be difficult to assign a special name.
Higher up the sky was violet, and this changed by insensible degrees
into the darkling blue of the zenith, which had to thank the light of
moon and stars alone for its existence. We wound steadily for a time
through valleys of ice, climbed white and slippery slopes, crossed a
number of crevasses, and after some time found ourselves beside a chasm
of great depth and width, which extended right and left as far as we
could see. We turned to the left, and marched along its edge in search
of a _pont_; but matters became gradually worse: other crevasses joined
on to the first one, and the further we proceeded the more riven and
dislocated the ice became. At length we reached a place where further
advance was impossible. Simond in his difficulty complained of the want
of light, and wished us to wait for the advancing day; I, on the
contrary, thought that we had light enough and ought to make use of it.
Here the thought occurred to me that Simond, having been only once
before to the top of the mountain, might not be quite clear about the
route; the glacier, however, changes within certain limits from year to
year, so that a general knowledge was all that could be expected, and we
trusted to our own muscles to make good any mistake in the way of
guidance. We now turned and retraced our steps along the edges of chasms
where the ice was disintegrated and insecure, and succeeded at length
in finding a bridge which bore us across the crevasse. This error caused
us the loss of an hour, and after walking for this time we could cast a
stone from the point we had attained to the place whence we had been
compelled to return.
[Sidenote: SÉRACS OF THE DÔME DU GOÛTER. 1857.]
Our way now lay along the face of a steep incline of snow, which was cut
by the fissure we had just passed, in a direction parallel to our route.
On the heights to our right, loose ice-crags seemed to totter, and we
passed two tracks over which the frozen blocks had rushed some short
time previously. We were glad to get out of the range of these terrible
projectiles, and still more so to escape the vicinity of that ugly
crevasse. To be killed in the open air would be a luxury, compared with
having the life squeezed out of one in the horrible gloom of these
chasms. The blush of the coming day became more and more intense; still
the sun himself did not appear, being hidden from us by the peaks of the
Aiguille du Midi, which were drawn clear and sharp against the
brightening sky. Right under this Aiguille were heaps of snow smoothly
rounded and constituting a portion of the sources whence the Glacier du
Géant is fed; these, as the day advanced, bloomed with a rosy light. We
reached the Petit Plateau, which we found covered with the remains of
ice avalanches; above us upon the crest of the mountain rose three
mighty bastions, divided from each other by deep vertical rents, with
clean smooth walls, across which the lines of annual bedding were drawn
like courses of masonry. From these, which incessantly renew themselves,
and from the loose and broken ice-crags near them, the boulders amid
which we now threaded our way had been discharged. When they fall their
descent must be sublime.
[Sidenote: THE LOST GUIDES. 1857.]
The snow had been gradually getting deeper, and the ascent more
wearisome, but superadded to this at the Petit Plateau was the
uncertainty of the footing between the blocks of ice. In many places
the space was merely covered by a thin crust, which, when trod upon,
instantly yielded, and we sank with a shock sometimes to the hips. Our
way next lay up a steep incline to the Grand Plateau, the depth and
tenderness of the snow augmenting as we ascended. We had not yet seen
the sun, but, as we attained the brow which forms the entrance to the
Grand Plateau, he hung his disk upon a spike of rock to our left, and,
surrounded by a glory of interference spectra of the most gorgeous
colours, blazed down upon us. On the Grand Plateau we halted and had our
frugal refreshment. At some distance to our left was the crevasse into
which Dr. Hamel's three guides were precipitated by an avalanche in
1820; they are still entombed in the ice, and some future explorer may
perhaps see them disgorged lower down, fresh and undecayed. They can
hardly reach the surface until they pass the snow-line of the glacier,
for above this line the quantity of snow that annually falls being in
excess of the quantity melted, the tendency would be to make the
ice-covering above them thicker. But it is also possible that the waste
of the ice underneath may have brought the bodies to the bed of the
glacier, where their very bones may have been ground to mud by an agency
which the hardest rocks cannot withstand.
[Sidenote: THE GUIDE TIRED. 1857.]
[Sidenote: A PERILOUS SLOPE. 1857.]
As the sun poured his light upon the Plateau the little snow-facets
sparkled brilliantly, sometimes with a pure white light, and at others
with prismatic colours. Contrasted with the white spaces above and
around us were the dark mountains on the opposite side of the valley of
Chamouni, around which fantastic masses of cloud were beginning to build
themselves. Mont Buet, with its cone of snow, looked small, and the
Brévent altogether mean; the limestone bastions of the Fys, however,
still presented a front of gloom and grandeur. We traversed the Grand
Plateau, and at length reached the base of an extremely steep incline
which stretched upwards towards the Corridor. Here, as if produced by a
fault, consequent upon the sinking of the ice in front, rose a vertical
precipice, from the coping of which vast stalactites of ice depended.
Previous to reaching this place I had noticed a haggard expression upon
the countenance of our guide, which was now intensified by the prospect
of the ascent before him. Hitherto he had always been in front, which
was certainly the most fatiguing position. I felt that I must now take
the lead, so I spoke cheerily to the man and placed him behind me.
Marking a number of points upon the slope as resting places, I went
swiftly from one to the other. The surface of the snow had been
partially melted by the sun and then refrozen, thus forming a
superficial crust, which bore the weight up to a certain point, and then
suddenly gave way, permitting the leg to sink to above the knee. The
shock consequent on this, and the subsequent effort necessary to
extricate the leg, were extremely fatiguing. My motion was complained of
as too quick, and my tracks as imperfect; I moderated the former, and,
to render my footholes broad and sure, I stamped upon the frozen crust,
and twisted my legs in the soft mass underneath,--a terribly exhausting
process. I thus led the way to the base of the Rochers Rouges, up to
which the fault already referred to had prolonged itself as a crevasse,
which was roofed at one place by a most dangerous-looking snow-bridge.
Simond came to the front; I drew his attention to the state of the snow,
and proposed climbing the Rochers Rouges; but, with a promptness unusual
with him, he replied that this was impossible; the bridge was our only
means of passing, and we must try it. We grasped our ropes, and dug our
feet firmly into the snow to check the man's descent if the _pont_ gave
way, but to our astonishment it bore him, and bore us safely after him.
The slope which we had now to ascend had the snow swept from its
surface, and was therefore firm ice. It was most dangerously steep, and,
its termination being the fretted coping of the precipice to which I
have referred, if we slid downwards we should shoot over this and be
dashed to pieces upon the ice below.[A] Simond, who had come to the
front to cross the crevasse, was now engaged in cutting steps, which he
made deep and large, so that they might serve us on our return. But the
listless strokes of his axe proclaimed his exhaustion; so I took the
implement out of his hands, and changed places with him. Step after step
was hewn, but the top of the Corridor appeared ever to recede from us.
Hirst was behind unoccupied, and could thus turn his thoughts to the
peril of our position: he _felt_ the angle on which we hung, and saw the
edge of the precipice, to which less than a quarter of a minute's slide
would carry us, and for the first time during the journey he grew giddy.
A cigar which he lighted for the purpose tranquilized him.
[Sidenote: WILL AND MUSCLE. 1857.]
I hewed sixty steps upon this slope, and each step had cost a minute, by
Hirst's watch. The Mur de la Côte was still before us, and on this the
guide-books informed us two or three hundred steps were sometimes found
necessary. If sixty steps cost an hour, what would be the cost of two
hundred? The question was disheartening in the extreme, for the time at
which we had calculated on reaching the summit was already passed, while
the chief difficulties remained unconquered. Having hewn our way along
the harder ice we reached snow. I again resorted to stamping to secure a
footing, and while thus engaged became, for the first time, aware of the
drain of force to which I was subjecting myself. The thought of being
absolutely exhausted had never occurred to me, and from first to last I
had taken no care to husband my strength. I always calculated that the
_will_ would serve me even should the muscles fail, but I now found that
mechanical laws rule man in the long run; that no effort of will, no
power of spirit, can draw beyond a certain limit upon muscular force.
The soul, it is true, can stir the body to action, but its function is
to excite and apply force, and not to create it.
While stamping forward through the frozen crust I was compelled to pause
at short intervals; then would set out again apparently fresh, to find,
however, in a few minutes that my strength was gone, and that I required
to rest once more. In this way I gained the summit of the Corridor, when
Hirst came to the front, and I felt some relief in stepping slowly after
him, making use of the holes into which his feet had sunk. He thus led
the way to the base of the Mur de la Côte, the thought of which had so
long cast a gloom upon us; here we left our rope behind us, and while
pausing I asked Simond whether he did not feel a desire to go to the
summit--"_Bien sûr_," was his reply, "_mais!_" Our guide's mind was so
constituted that the "_mais_" seemed essential to its peace. I stretched
my hand towards him, and said, "Simond, we must do it." One thing alone
I felt could defeat us: the usual time of the ascent had been more than
doubled, the day was already far spent, and if the ascent would throw
our subsequent descent into night it could not be contemplated.
[Sidenote: A DOZE ON THE CALOTTE. 1857.]
We now faced the Mur, which was by no means so bad as we had expected.
Driving the iron claws of our boots into the scars made by the axe, and
the spikes of our bâtons into the slope above our feet, we ascended
steadily until the summit was attained, and the top of the mountain rose
clearly above us. We congratulated ourselves upon this; but Simond,
probably fearing that our joy might become too full, remarked, "_Mais le
sommet est encore bien loin!_" It was, alas! too true. The snow became
soft again, and our weary limbs sank in it as before. Our guide went on
in front, audibly muttering his doubts as to our ability to reach the
top, and at length he threw himself upon the snow, and exclaimed, "_Il
faut y renoncer!_" Hirst now undertook the task of rekindling the
guide's enthusiasm, after which Simond rose, exclaiming, "_Ah! comme ça
me fait mal aux genoux_," and went forward. Two rocks break through the
snow between the summit of the Mur and the top of the mountain; the
first is called the Petits Mulets, and the highest the Derniers Rochers.
At the former of these we paused to rest, and finished our scanty store
of wine and provisions. We had not a bit of bread nor a drop of wine
left; our brandy flasks were also nearly exhausted, and thus we had to
contemplate the journey to the summit, and the subsequent descent to the
Grands Mulets, without the slightest prospect of physical refreshment.
The almost total loss of two nights' sleep, with two days' toil
superadded, made me long for a few minutes' doze, so I stretched myself
upon a composite couch of snow and granite, and immediately fell asleep.
My friend, however, soon aroused me. "You quite frighten me," he said;
"I have listened for some minutes, and have not heard you breathe once."
I had, in reality, been taking deep draughts of the mountain air, but so
silently as not to be heard.
I now filled our empty wine-bottle with snow and placed it in the
sunshine, that we might have a little water on our return. We then rose;
it was half-past two o'clock; we had been upwards of twelve hours
climbing, and I calculated that, whether we reached the summit or not,
we could at all events work _towards_ it for another hour. To the sense
of fatigue previously experienced, a new phenomenon was now added--the
beating of the heart. We were incessantly pulled up by this, which
sometimes became so intense as to suggest danger. I counted the number
of paces which we were able to accomplish without resting, and found
that at the end of every twenty, sometimes at the end of fifteen, we
were compelled to pause. At each pause my heart throbbed audibly, as I
leaned upon my staff, and the subsidence of this action was always the
signal for further advance. My breathing was quick, but light and
unimpeded. I endeavoured to ascertain whether the hip-joint, on account
of the diminished atmospheric pressure, became loosened, so as to throw
the weight of the leg upon the surrounding ligaments, but could not be
certain about it. I also sought a little aid and encouragement from
philosophy, endeavouring to remember what great things had been done by
the accumulation of small quantities, and I urged upon myself that the
present was a case in point, and that the summation of distances twenty
paces each must finally place us at the top. Still the question of time
left the matter long in doubt, and until we had passed the Derniers
Rochers we worked on with the stern indifference of men who were doing
their duty, and did not look to consequences. Here, however, a gleam of
hope began to brighten our souls; the summit became visibly nearer,
Simond showed more alacrity; at length success became certain, and at
half-past three P.M. my friend and I clasped hands upon the top.
[Sidenote: THE SUMMIT ATTAINED. 1857.]
The summit of the mountain is an elongated ridge, which has been
compared to the back of an ass. It was perfectly manifest that we were
dominant over all other mountains; as far as the eye could range Mont
Blanc had no competitor. The summits which had looked down upon us in
the morning were now far beneath us. The Dôme du Goûter, which had held
its threatening _séracs_ above us so long, was now at our feet. The
Aiguille du Midi, Mont Blanc du Tacul, and the Monts Maudits, the
Talèfre with its surrounding peaks, the Grand Jorasse, Mont Mallet, and
the Aiguille du Géant, with our own familiar glaciers, were all below
us. And as our eye ranged over the broad shoulders of the mountain, over
ice hills and valleys, plateaux and far-stretching slopes of snow, the
conception of its magnitude grew upon us, and impressed us more and
more.
[Sidenote: CLOUDS FROM THE SUMMIT. 1857.]
The clouds were very grand--grander indeed than anything I had ever
before seen. Some of them seemed to hold thunder in their breasts, they
were so dense and dark; others, with their faces turned sunward, shone
with the dazzling whiteness of the mountain snow; while others again
built themselves into forms resembling gigantic elm trees, loaded with
foliage. Towards the horizon the luxury of colour added itself to the
magnificent alternations of light and shade. Clear spaces of amber and
ethereal green embraced the red and purple cumuli, and seemed to form
the cradle in which they swung. Closer at hand squally mists, suddenly
engendered, were driven hither and thither by local winds; while the
clouds at a distance lay "like angels sleeping on the wing," with
scarcely visible motion. Mingling with the clouds, and sometimes rising
above them, were the highest mountain heads, and as our eyes wandered
from peak to peak, onwards to the remote horizon, space itself seemed
more vast from the manner in which the objects which it held were
distributed.
[Sidenote: INTENSITY OF SOUND. 1857.]
I wished to repeat the remarkable experiment of De Saussure upon sound,
and for this purpose had requested Simond to bring a pistol from
Chamouni; but in the multitude of his cares he forgot it, and in lieu of
it my host at the Montanvert had placed in two tin tubes, of the same
size and shape, the same amount of gunpowder, securely closing the tubes
afterwards, and furnishing each of them with a small lateral aperture.
We now planted one of them upon the snow, and bringing a strip of amadou
into communication with the touchhole, ignited its most distant end: it
failed; we tried again, and were successful, the explosion tearing
asunder the little case which contained the powder. The sound was
certainly not so great as I should have expected from an equal quantity
of powder at the sea level.[B]
The snow upon the summit was indurated, but of an exceedingly fine
grain, and the beautiful effect already referred to as noticed upon the
Stelvio was strikingly manifest. The hole made by driving the bâton into
the snow was filled with a delicate blue light; and, by management, its
complementary pinky yellow could also be produced. Even the iron spike
at the end of the bâton made a hole sufficiently deep to exhibit the
blue colour, which certainly depends on the size and arrangement of the
snow crystals. The firmament above us was without a cloud, and of a
darkness almost equal to that which surrounded the moon at 2 A.M. Still,
though the sun was shining, a breeze, whose tooth had been sharpened by
its passage over the snow-fields, searched us through and through. The
day was also waning, and, urged by the warnings of our ever prudent
guide, we at length began the descent.
[Sidenote: AN UNEXPECTED GLISSADE. 1857.]
Gravity was now in our favour, but gravity could not entirely spare our
wearied limbs, and where we sank in the snow we found our downward
progress very trying. I suffered from thirst, but after we had divided
the liquefied snow at the Petits Mulets amongst us we had nothing to
drink. I crammed the clean snow into my mouth, but the process of
melting was slow and tantalizing to a parched throat, while the chill
was painful to the teeth. We marched along the Corridor, and crossed
cautiously the perilous slope on which we had cut steps in the morning,
breathing more freely after we had cleared the ice-precipice before
described. Along the base of this precipice we now wound, diverging from
our morning's track, in order to get surer footing in the snow; it was
like flour, and while descending to the Grand Plateau we sometimes sank
in it nearly to the waist. When I endeavoured to squeeze it, so as to
fill my flask, it at first refused to cling together, behaving like so
much salt; the heat of the hand, however, soon rendered it a little
moist, and capable of being pressed into compact masses. The sun met us
here with extraordinary power; the heat relaxed my muscles, but when
fairly immersed in the shadow of the Dôme du Goûter, the coolness
restored my strength, which augmented as the evening advanced. Simond
insisted on the necessity of haste, to save us from the perils of
darkness. "_On peut périr_" was his repeated admonition, and he was
quite right. We reached the region of _ponts_, more weary, but, in
compensation, more callous, than we had been in the morning, and moved
over the soft snow of the bridges as if we had been walking upon eggs.
The valley of Chamouni was filled with brown-red clouds, which crept
towards us up the mountain; the air around and above us was, however,
clear, and the chastened light told us that day was departing. Once as
we hung upon a steep slope, where the snow was exceedingly soft, Hirst
omitted to make his footing sure; the soft mass gave way, and he fell,
uttering a startled shout as he went down the declivity. I was attached
to him, and, fixing my feet suddenly in the snow, endeavoured to check
his fall, but I seemed a mere feather in opposition to the force with
which he descended.[C] I fell, and went down after him; and we carried
quite an avalanche of snow along with us, in which we were almost
completely hidden at the bottom of the slope. All further dangers,
however, were soon past, and we went at a headlong speed to the base of
the Grands Mulets; the sound of our bâtons against the rocks calling
Huxley forth. A position more desolate than his had been can hardly be
imagined. For seventeen hours he had been there. He had expected us at
two o'clock in the afternoon; the hours came and passed, and till seven
in the evening he had looked for us. "To the end of my life," he said,
"I shall never forget the sound of those bâtons." It was his turn now to
nurse me, which he did, repaying my previous care of him with high
interest. We were all soon stretched, and, in spite of cold and hard
boards, I slept at intervals; but the night, on the whole, was a weary
one, and we rose next morning with muscles more tired than when we lay
down.
[Sidenote: BLIND AMID THE CREVASSES. 1857.]
_Friday, 14th August._--Hirst was almost blind this morning; and our
guide's eyes were also greatly inflamed. We gathered our things
together, and bade the Grands Mulets farewell. It had frozen hard during
the night, and this, on the steeper slopes, rendered the footing very
insecure. Simond, moreover, appeared to be a little bewildered, and I
sometimes preceded him in cutting the steps, while Hirst moved among the
crevasses like a blind man; one of us keeping near him, so that he might
feel for the actual places where our feet had rested, and place his own
in the same position. It cost us three hours to cross from the Grands
Mulets to the Pierre a l'Echelle, where we discarded our leggings, had a
mouthful of food, and a brief rest. Once upon the safe earth Simond's
powers seemed to be restored, and he led us swiftly downwards to the
little auberge beside the Cascade du Tard, where we had some excellent
lemonade, equally choice cognac, fresh strawberries and cream. How sweet
they were, and how beautiful we thought the peasant girl who served
them! Our guide kept a little hotel, at which we halted, and found it
clean and comfortable. We were, in fact, totally unfit to go elsewhere.
My coat was torn, holes were kicked through my boots, and I was
altogether ragged and shabby. A warm bath before dinner refreshed all
mightily. Dense clouds now lowered upon Mont Blanc, and we had not been
an hour at Chamouni when the breaking up of the weather was announced by
a thunder-peal. We had accomplished our journey just in time.
FOOTNOTES:
[A] Those acquainted with the mountain will at once recognise the grave
error here committed. In fact on starting from the Grands Mulets we had
crossed the glacier too far, and throughout were much too close to the
Dôme du Goûter.
[B] I fired the second case in a field in Hampshire, and, as far as my
memory enabled me to make the comparison, found its sound considerably
_denser_, if I may use the expression. In 1859 I had a pistol fired at
the summit of Mont Blanc: its sound was sensibly feebler and _shorter_
than in the valley; it resembled somewhat the discharge of a cork from a
champagne bottle, though much louder, but it could not be at all
compared to the sound of a common cracker.
[C] I believe that I could stop him now (1860).
(12.)
[Sidenote: HAPPY EVENINGS. 1857.]
After our return we spent every available hour upon the ice, working at
questions which shall be treated under their proper heads, each day's
work being wound up by an evening of perfect enjoyment. Roast mutton and
fried potatoes were our incessant fare, for which, after a little
longing for a change at first, we contracted a final and permanent love.
As the year advanced, moreover, and the grass sprouted with augmented
vigour on the slopes of the Montanvert, the mutton, as predicted by our
host, became more tender and juicy. We had also some capital Sallenches
beer, cold as the glacier water, but effervescent as champagne. Such
were our food and drink. After dinner we gathered round the pine-fire,
and I can hardly think it possible for three men to be more happy than
we then were. It was not the goodness of the conversation, nor any high
intellectual element, which gave the charm to our gatherings; the
gladness grew naturally out of our own perfect health, and out of the
circumstances of our position. Every fibre seemed a repository of latent
joy, which the slightest stimulus sufficed to bring into conscious
action.
[Sidenote: A GLACIER "BLOWER." 1857.]
On the 17th I penetrated with Simond through thick gloom to the Tacul;
on the 18th we set stakes at the same place: on the same day, while
crossing the medial moraine of the Talèfre, a little below the cascade,
a singular noise attracted my attention; it seemed at first as if a
snake were hissing about my feet. On changing my position the sound
suddenly ceased, but it soon recommenced. There was some snow upon the
glacier, which I removed, and placed my ear close to the ice, but it was
difficult to fix on the precise spot from which the sound issued. I cut
away the disintegrated portion of the surface, and at length discovered
a minute crack, from which a stream of air issued, which I could feel as
a cold blast against my hand. While cutting away the surface further, I
stopped the little "blower." A marmot screamed near me, and while I
paused to look at the creature scampering up the crags, the sound
commenced again, changing its note variously--hissing like a snake,
singing like a kettle, and sometimes chirruping intermittently like a
bird. On passing my fingers to and fro over the crack, I obtained a
succession of audible puffs; the current was sufficiently strong to blow
away the corner of a gauze veil held over the fissure. Still the crack
was not wide enough to permit of the entrance of my finger nail; and to
issue with such force from so minute a rent the air must have been under
considerable pressure. The origin of the blower was in all probability
the following:--When the ice is recompacted after having descended a
cascade, it is next to certain that chambers of air will be here and
there enclosed, which, being powerfully squeezed afterwards, will issue
in the manner described whenever a crack in the ice furnishes it with a
means of escape. In my experiments on flowing mud, for example, the air
entrapped in the mass while descending from the sluice into the trough,
bursts in bubbles from the surface at a short distance downwards.
[Sidenote: A DIFFICULT LINE. 1857.]
I afterwards examined the Talèfre cascade from summit to base, with
reference to the structure, until at the close of the day thickening
clouds warned me off. I went down the glacier at a trot, guided by the
boulders capped with little cairns which marked the route. The track
which I had pursued for the last five weeks amid the crevasses near
l'Angle was this day barely passable. The glacier had changed, my work
was drawing to a close, and, as I looked at the objects which had now
become so familiar to me, I felt that, though not viscous, the ice did
not lack the quality of "adhesiveness," and I felt a little sad at the
thought of bidding it so soon farewell.
At some distance below the Montanvert the Mer de Glace is riven from
side to side by transverse crevasses: these fissures indicate that the
glacier where they occur is in a state of longitudinal strain which
produces transverse fracture. I wished to ascertain the amount of
stretching which the glacier here demanded, and which the ice was not
able to give; and for this purpose desired to compare the velocity of a
line set out across the fissured portion with that of a second line
staked out across the ice before it had become thus fissured. A previous
inspection of the glacier through the telescope of our theodolite
induced us to fix on a place which, though much riven, still did not
exclude the hope of our being able to reach the other side. Each of us
was, as usual, armed with his own axe; and carrying with us suitable
stakes, my guide and myself entered upon this portion of the glacier on
the morning of the 19th of August.
[Sidenote: "NOUS NOUS TROUVERONS PERDUS!" 1857.]
I was surprised on entering to find some veins of white ice, which from
their position and aspect appeared to be derived from the Glacier du
Géant; but to these I shall subsequently refer. Our work was extremely
difficult; we penetrated to some distance along one line, but were
finally forced back, and compelled to try another. Right and left of us
were profound fissures, and once a cone of ice forty feet high leaned
quite over our track. In front of us was a second leaning mass borne by
a mere stalk, and so topheavy that one wondered why the slight pedestal
on which it rested did not suddenly crack across. We worked slowly
forwards, and soon found ourselves in the shadow of the topheavy mass
above referred to; and from which I escaped with a wounded hand, caused
by over-haste. Simond surmounted the next ridge and exclaimed, "_Nous
nous trouverons perdus!_" I reached his side, and on looking round the
place saw that there was no footing for man. The glacier here, as shown
in the frontispiece, was cut up into thin wedges, separated from each
other by profound chasms, and the wedges were so broken across as to
render creeping along their edges quite impossible. Thus brought to a
stand, I fixed a stake at the point where we were forced to halt, and
retreated along edges of detestable granular ice, which fell in showers
into the crevasses when struck by the axe. At one place an exceedingly
deep fissure was at our left, which was joined, at a sharp angle, by
another at our right, and we were compelled to cross at the place of
intersection: to do this we had to trust ourselves to a projecting knob
of that vile rotten ice which I had learned to fear since my experience
of it on the Col du Géant. We finally escaped, and set out our line at
another place, where the glacier, though badly cut, was not impassable.
[Sidenote: FAREWELL TO THE MONTANVERT. 1857.]
On the 20th we made a series of final measurements at the Tacul, and
determined the motion of two lines which we had set out the previous
day. On the 21st we quitted the Montanvert; I had been there from the
15th of July, and the longer I remained the better I liked the
establishment and the people connected with it. It was then managed by
Joseph Tairraz and Jules Charlet, both of whom showed us every
attention. In 1858 and 1859 I had occasion to revisit the establishment,
which was then managed by Jules and his brother, and found in it the
same good qualities. During my winter expedition of 1859 I also found
the same readiness to assist me in every possible way; honest Jules
expressing his willingness to ascend through the snow to the auberge if
I thought his presence would in any degree contribute to my comfort.
We crossed the glacier, and descended by the Chapeau to the Cascade des
Bois, the inclination of which and of the lower portion of the glacier
we then determined. The day was magnificent. Looking upwards, the
Aiguilles de Charmoz and du Dru rose right and left like sentinels of
the valley, while in front of us the ice descended the steep, a
bewildering mass of crags and chasms. At the other side was the
pine-clad slope of the Montanvert. Further on the Aiguille du Midi threw
its granite pyramid between us and Mont Blanc; on the Dôme du Goûter the
_séracs_ of the mountain were to be seen, while issuing as if from a
cleft in the mountain side the Glacier des Bossons thrust through the
black pines its snowy tongue. Below us was the beautiful valley of
Chamouni itself, through which the Arve and Arveiron rushed like
enlivening spirits. We finally examined a grand old moraine produced by
a Mer de Glace of other ages, when the ice quite crossed the valley of
Chamouni and abutted against the opposite mountain-wall.
[Sidenote: EDOUARD SIMOND. 1857.]
Simond had proved himself a very valuable assistant; he was intelligent
and perfectly trustworthy; and though the peculiar nature of my work
sometimes caused me to attempt things against which his prudence
protested, he lacked neither strength nor courage. On reaching Chamouni
and adding up our accounts, I found that I had not sufficient cash to
pay him; money was waiting for me at the post-office in Geneva, and
thither it was arranged that my friend Hirst should proceed next
morning, while I was to await the arrival of the money at Chamouni. My
guide heard of this arrangement, and divined its cause: he came to me,
and in the most affectionate manner begged of me to accept from him the
loan of 500 francs. Though I did not need the loan, the mode in which it
was offered to me augmented the kindly feelings which I had long
entertained towards Simond, and I may add that my intercourse with him
since has served only to confirm my first estimate of his worthiness.
EXPEDITION OF 1858.
(13.)
[Sidenote: DOUBTS REGARDING STRUCTURE. 1858.]
I had confined myself during the summer of 1857 to the Mer de Glace and
its tributaries, desirous to make my knowledge accurate rather than
extensive. I had made the acquaintance of all accessible parts of the
glacier, and spared no pains to master both the details and the meaning
of the laminated structure of the ice, but I found no fact upon which I
could take my stand and say to an advocate of an opposing theory, "This
is unassailable." In experimental science we have usually the power of
changing the conditions at pleasure; if Nature does not reply to a
question we throw it into another form; a combining of conditions is, in
fact, the essence of experiment. To meet the requirements of the present
question, I could not twist the same glacier into various shapes, and
throw it into different states of strain and pressure; but I might, by
visiting many glaciers, find all needful conditions fulfilled in detail,
and by observing these I hoped to confer upon the subject the character
and precision of a true experimental inquiry.
The summer of 1858 was accordingly devoted to this purpose, when I had
the good fortune to be accompanied by Professor Ramsay, the author of
some extremely interesting papers upon ancient glaciers. Taking Zürich,
Schaffhausen, and Lucerne in our way, we crossed the Brünig on the 22nd
of July, and met my guide, Christian Lauener, at Meyringen. On the 23rd
we visited the glacier of Rosenlaui, and the glacier of the
Schwartzwald, and reached Grindelwald in the evening of the same day. My
expedition with Mr. Huxley had taught me that the Lower Grindelwald
Glacier was extremely instructive, and I was anxious to see many parts
of it once more; this I did, in company with Ramsay, and we also spent a
day upon the upper glacier, after which our path lay over the Strahleck
to the glaciers of the Aar and of the Rhone.
PASSAGE OF THE STRAHLECK.
(14.)
[Sidenote: A GLOOMY PROSPECT. 1858.]
On Monday, the 26th of July, we were called at 4 A.M., and found the
weather very unpromising, but the two mornings which preceded it had
also been threatening without any evil result. There was, it is true,
something more than usually hostile in the aspect of the clouds which
sailed sullenly from the west, and smeared the air and mountains as if
with the dirty smoke of a manufacturing town. We despatched our coffee,
went down to the bottom of the Grindelwald valley, up the opposite
slope, and were soon amid the gloom of the pines which partially cover
it. On emerging from these, a watery gleam on the mottled head of the
Eiger was the only evidence of direct sunlight in that direction. To our
left was the Wetterhorn surrounded by wild and disorderly clouds,
through the fissures of which the morning light glared strangely. For a
time the Heisse Platte was seen, a dark brown patch amid the ghastly
blue which overspread the surrounding slopes of snow. The clouds once
rolled up, and revealed for a moment the summits of the Viescherhörner;
but they immediately settled down again, and hid the mountains from top
to base. Soon afterwards they drew themselves partially aside, and a
patch of blue over the Strahleck gave us hope and pleasure. As we
ascended, the prospect in front of us grew better, but that behind
us--and the wind came from behind--grew worse. Slowly and stealthily the
dense neutral-tint masses crept along the sides of the mountains, and
seemed to dog us like spies; while over the glacier hung a thin veil of
fog, through which gleamed the white minarets of the ice.
[Sidenote: ICE CASCADE AND PROTUBERANCES. 1858.]
[Sidenote: DIRT-BANDS OF THE STRAHLECK BRANCH. 1858.]
When we first spoke of crossing the Strahleck, Lauener said it would be
necessary to take two guides at least; but after a day's performance on
the ice he thought we might manage very well by taking, in addition to
himself, the herd of the alp, over the more difficult part of the pass.
He had further experience of us on the second day, and now, as we
approached the herd's hut, I was amused to hear him say that he thought
any assistance beside his own unnecessary. Relying upon ourselves,
therefore, we continued our route, and were soon upon the glacier, which
had been rendered smooth and slippery through the removal of its
disintegrated surface by the warm air. Crossing the Strahleck branch of
the glacier to its left side, we climbed the rocks to the grass and
flowers which clothe the slopes above them. Our way sometimes lay over
these, sometimes along the beds of streams, across turbulent brooks, and
once around the face of a cliff, which afforded us about an inch of
ledge to stand upon, and some protruding splinters to lay hold of by the
hands. Having reached a promontory which commanded a fine view of the
glacier, and of the ice cascade by which it was fed, I halted, to check
the observations already made from the side of the opposite mountain.
Here, as there, cliffy ridges were seen crossing the cascade of the
glacier, with interposed spaces of dirt and débris--the former being
toned down, and the latter squeezed towards the base of the fall, until
finally the ridges swept across the glacier, in gentle swellings, from
side to side; while the valleys between them, holding the principal
share of the superficial impurity, formed the cradles of the so-called
Dirt-Bands. These swept concentric with the protuberances across the
glacier, and remained upon its surface even after the swellings had
disappeared. The swifter flow of the centre of the glacier tends of
course incessantly to lengthen the loops of the bands, and to thrust the
summits of the curves which they form more and more in advance of their
lateral portions. The depressions between the protuberances appeared to
be furrowed by minor wrinkles, as if the ice of the depressions had
yielded more than that of the protuberances. This, I think, is extremely
probable, though it has never yet been proved. Three stakes, placed, one
on the summit, another on the frontal slope, and another at the base of
a protuberance, would, I think, move with unequal velocities. They
would, I think, show that, upon the large and general motion of the
glacier, smaller motions are superposed, as minor oscillations are known
to cover parasitically the large ones of a vibrating string. Possibly,
also, the dirt-bands may owe something to the squeezing of impurities
out of the glacier to its surface in the intervals between the
swellings. From our present position we could also see the swellings on
the Viescherhörner branch of the glacier, in the valleys between which
coarse shingle and débris were collected, which would form dirt-bands if
they could. On neither branch, however, do the bands attain the
definition and beauty which they possess upon the Mer de Glace.
After an instructive lesson we faced our task once more, passing amid
crags and boulders, and over steep moraines, from which the stones
rolled down upon the slightest disturbance. While crossing a slope of
snow with an inclination of 45°, my footing gave way, I fell, but turned
promptly on my face, dug my staff deeply into the snow, and arrested the
motion before I had slid a dozen yards. Ramsay was behind me,
speculating whether he should be able to pass the same point without
slipping; before he reached it, however, the snow yielded, he fell, and
slid swiftly downwards. Lauener, whose attention had been aroused by my
fall, chanced to be looking round when Ramsay's footing yielded. With
the velocity of a projectile he threw himself upon my companion, seized
him, and brought him to rest before he had reached the bottom of the
slope. The act made a very favourable impression upon me, it was so
prompt and instinctive. An eagle could not swoop upon its prey with more
directness of aim and swiftness of execution.
[Sidenote: ICE CLIFFS THROUGH THE FOG. 1858.]
While this went on the clouds were playing hide and seek with the
mountains. The ice-crags and pinnacles to our left, looming through the
haze, seemed of gigantic proportions, reminding one of the Hades of
Byron's 'Cain.'
"How sunless and how vast are these dim realms!"
We climbed for some time along the moraine which flanks the cascade, and
on reaching the level of the brow Lauener paused, cast off his knapsack,
and declared for breakfast. While engaged with it the dense clouds which
had crammed the gorge and obscured the mountains, all melted away, and a
scene of indescribable magnificence was revealed. Overhead the sky
suddenly deepened to dark blue, and against it the Finsteraarhorn
projected his dark and mighty mass. Brown spurs jutted from the
mountain, and between them were precipitous snow-slopes, fluted by the
descent of rocks and avalanches, and broken into ice-precipices lower
down. Right in front of us, and from its proximity more gigantic to the
eye, was the Schreckhorn, while from couloirs and mountain-slopes the
matter of glaciers yet to be was poured into the vast basin on the rim
of which we now stood.
[Sidenote: MUTATIONS OF THE CLOUDS. 1858.]
This it was next our object to cross; our way lying in part through deep
snow-slush, the scene changing perpetually from blue heaven to gray haze
which massed itself at intervals in dense clouds about the mountains.
After crossing the basin our way lay partly over slopes of snow, partly
over loose shingle, and at one place along the edge of a formidable
precipice of rock. We sat down sometimes to rest, and during these
pauses, though they were very brief, the scene had time to go through
several of its Protean mutations. At one moment all would be perfectly
serene, no cloud in the transparent air to tell us that any portion of
it was in motion, while the blue heaven threw its flattened arch over
the magnificent amphitheatre. Then in an instant, from some local
cauldron, the vapour would boil up suddenly, eddying wildly in the air,
which a moment before seemed so still, and enveloping the entire scene.
Thus the space enclosed by the Finsteraarhorn, the Viescherhörner, and
the Schreckhorn, would at one moment be filled with fog to the mountain
heads, every trace of which a few minutes sufficed to sweep away,
leaving the unstained blue of heaven behind it, and the mountains
showing sharp and jagged outlines in the glassy air. One might be almost
led to imagine that the vapour molecules endured a strain similar to
that of water cooled below its freezing point, or heated beyond its
boiling point; and that, on the strain being relieved by the sudden
yielding of the opposing force, the particles rushed together, and thus
filled in an instant the clear atmosphere with aqueous precipitation.
I had no idea that the Strahleck was so fine a pass. Whether it is the
quality of my mind to take in the glory of the present so intensely as
to make me forgetful of the glory of the past, I know not, but it
appeared to me that I had never seen anything finer than the scene from
the summit. The amphitheatre formed by the mountains seemed to me of
exceeding magnificence; nor do I think that my feeling was subjective
merely; for the simple magnitude of the masses which built up the
spectacle would be sufficient to declare its grandeur. Looking down
towards the Glacier of the Aar, a scene of wild beauty and desolation
presented itself. Not a trace of vegetation could be seen along the
whole range of the bounding mountains; glaciers streamed from their
shoulders into the valley beneath, where they welded themselves to form
the Finsteraar affluent of the Unteraar glacier.
[Sidenote: DESCENT OF THE CRAGS. 1858.]
After a brief pause, Lauener again strapped on his knapsack, and
tempered both will and muscles by the remark, that our worst piece of
work was now before us. From the place where we sat, the mountain fell
precipitously for several hundred feet; and down the weathered crags,
and over the loose shingle which encumbered their ledges, our route now
lay. Lauener was in front, cool and collected, lending at times a hand
to Ramsay, and a word of encouragement to both of us, while I brought up
the rear. I found my full haversack so inconvenient that I once or twice
thought of sending it down the crags in advance of me, but Lauener
assured me that it would be utterly destroyed before reaching the
bottom. My complaint against it was, that at critical places it
sometimes came between me and the face of the cliff, pushing me away
from the latter so as to throw my centre of gravity almost beyond the
base intended to support it. We came at length upon a snow-slope, which
had for a time an inclination of 50°; then once more to the rocks; again
to the snow, which was both steep and deep. Our bâtons were at least six
feet long: we drove them into the snow to secure an anchorage, but they
sank to their very ends, and we merely retained a length of them
sufficient for a grasp. This slope was intersected by a so-called
Bergschrund, the lower portion of the slope being torn away from its
upper portion so as to form a crevasse that extended quite round the
head of the valley. We reached its upper edge; the chasm was partially
filled with snow, which brought its edges so near that we cleared it by
a jump. The rest of the slope was descended by a _glissade_. Each sat
down upon the snow, and the motion, once commenced, swiftly augmented to
the rate of an avalanche, and brought us pleasantly to the bottom.
[Sidenote: THROUGH GLOOM TO THE GRIMSEL. 1858.]
As we looked from the heights, we could see that the valley through
which our route lay was filled with gray fog: into this we soon plunged,
and through it we made our way towards the Abschwung. The inclination of
the glacier was our only guide, for we could see nothing. Reaching the
confluence of the Finsteraar and Lauteraar branches, we went downwards
with long swinging strides, close alongside the medial moraine of the
trunk glacier. The glory of the morning had its check in the dull gloom
of the evening. Across streams, amid dirt-cones and glacier-tables, and
over the long reach of shingle which covers the end of the glacier, we
plodded doggedly, and reached the Grimsel at 7 P.M., the journey having
cost a little more than 14 hours.
(15.)
[Sidenote: ANCIENT GLACIER ACTION. 1858.]
We made the Grimsel our station for a day, which was spent in examining
the evidences of ancient glacier action in the valley of Hasli. Near the
Hospice, but at the opposite side of the Aar, rises a mountain-wall of
hard granite, on which the flutings and groovings are magnificently
preserved. After a little practice the eye can trace with the utmost
precision the line which marks the level of the ancient ice: above this
the crags are sharp and rugged; while below it the mighty grinder has
rubbed off the pinnacles of the rocks and worn their edges away. The
height to which this action extends must be nearly two thousand feet
above the bed of the present valley. It is also easy to see the depth to
which the river has worked its channel into the ancient rocks. In some
cases the road from Guttanen to the Grimsel lay right over the polished
rocks, asperities being supplied by the chisel of man in order to
prevent travellers from slipping on their slopes. Here and there also
huge protuberant crags were rounded into domes almost as perfect as if
chiselled by art. To both my companion and myself this walk was full of
instruction and delight.
On the 28th of July we crossed the Grimsel pass, and traced the
scratchings to the very top of it. Ramsay remarked that their direction
changed high up the pass, as if a tributary from the summit had produced
them, while lower down they merged into the general direction of the
glacier which had filled the principal valley. From the summit of the
Mayenwand we had a clear view of the glacier of the Rhone; and to see
the lower portion of this glacier to advantage no better position can be
chosen. The dislocation of its cascade, the spreading out of the ice
below, its system of radial crevasses, and the transverse sweep of its
structural groovings, may all be seen. A few hours afterwards we were
among the wild chasms at the brow of the ice-fall, where we worked our
way to the centre of the ice, but were unable to attain the opposite
side.
Having examined the glacier both above and below the cascade, we went
down the valley to Viesch, and ascended thence, on the 30th of July, to
the Hôtel Jungfrau on the slopes of the Æggischhorn. On the following
day we climbed to the summit of the mountain, and from a sheltered nook
enjoyed the glorious prospect which it commands. The wind was strong,
and fleecy clouds flew over the heavens; some of which, as they formed
and dispersed themselves about the flanks of the Aletschhorn, showed
extraordinary iridescences.
[Sidenote: THE MÄRJELEN SEE. 1858.]
The sunbeams called us early on the morning of the 1st of August. No
cloud rested on the opposite range of the Valais mountains, but on
looking towards the Æggischhorn we found a cap upon its crest; we looked
again--the cap had disappeared and a serene heaven stretched overhead.
As we breasted the alp the moon was still in the sky, paling more and
more before the advancing day; a single hawk swung in the atmosphere
above us; clear streams babbled from the hills, the louder sounds
reposing on a base of music; while groups of cows with tinkling bells
browsed upon the green alp. Here and there the grass was dispossessed,
and the flanks of the mountain were covered by the blocks which had been
cast down from the summit. On reaching the plateau at the base of the
final pyramid, we rounded the mountain to the right and came over the
lonely and beautiful Märjelen See. No doubt the hollow which this lake
fills had been scooped out in former ages by a branch of the Aletsch
glacier; but long ago the blue ice gave place to blue water. The glacier
bounds it at one side by a vertical wall of ice sixty feet in height:
this is incessantly undermined, a roof of crystal being formed over the
water, till at length the projecting mass, becoming too heavy for its
own rigidity, breaks and tumbles into the lake. Here, attacked by sun
and air, its blue surface is rendered dazzlingly white, and several
icebergs of this kind now floated in the sunlight; the water was of a
glassy smoothness, and in its blue depths each ice mass doubled itself
by reflection.[A]
[Sidenote: THE ALETSCH GLACIER. 1858.]
The Aletsch is the grandest glacier in the Alps: over it we now stood,
while the bounding mountains poured vast feeders into the noble stream.
The Jungfrau was in front of us without a cloud, and apparently so near
that I proposed to my guide to try it without further preparation. He
was enthusiastic at first, but caution afterwards got the better of his
courage. At some distance up the glacier the snow-line was distinctly
drawn, and from its edge upwards the mighty shoulders of the hills were
heavy laden with the still powdery material of the glacier.
Amid blocks and débris we descended to the ice: the portion of it which
bounded the lake had been sapped, and a space of a foot existed between
ice and water: numerous chasms were formed here, the mass being thus
broken, preparatory to being sent adrift upon the lake. We crossed the
glacier to its centre, and looking down it the grand peaks of the
Mischabel, the noble cone of the Weisshorn, and the dark and stern
obelisk of the Matterhorn, formed a splendid picture. Looking upwards, a
series of most singularly contorted dirt-bands revealed themselves upon
the surface of the ice. I sought to trace them to their origin, but was
frustrated by the snow which overspread the upper portion of the
glacier. Along this we marched for three hours, and came at length to
the junction of the four tributary valleys which pour their frozen
streams into the great trunk valley. The glory of the day, and that joy
of heart which perfect health confers, may have contributed to produce
the impression, but I thought I had never seen anything to rival in
magnificence the region in the heart of which we now found ourselves. We
climbed the mountain on the right-hand side of the glacier, where,
seated amid the riven and weather-worn crags, we fed our souls for hours
on the transcendent beauty of the scene.
[Sidenote: A CHAMOIS DECEIVED. 1858.]
We afterwards redescended to the glacier, which at this place was
intersected by large transverse crevasses, many of which were apparently
filled with snow, while over others a thin and treacherous roof was
thrown. In some cases the roof had broken away, and revealed rows of
icicles of great length and transparency pendent from the edges. We at
length turned our faces homewards, and looking down the glacier I saw
at a great distance something moving on the ice. I first thought it was
a man, though it seemed strange that a man should be there alone. On
drawing my guide's attention to it he at once pronounced it to be a
chamois, and I with my telescope immediately verified his statement. The
creature bounded up the glacier at intervals, and sometimes the vigour
of its spring showed that it had projected itself over a crevasse. It
approached us sometimes at full gallop: then would stop, look toward us,
pipe loudly, and commence its race once more. It evidently made the
reciprocal mistake to my own, imagining us to be of its own kith and
kin. We sat down upon the ice the better to conceal our forms, and to
its whistle our guide whistled in reply. A joyous rush was the
creature's first response to the signal; but it afterwards began to
doubt, and its pauses became more frequent. Its form at times was
extremely graceful, the head erect in the air, its apparent uprightness
being augmented by the curvature which threw its horns back. I watched
the animal through my glass until I could see the glistening of its
eyes; but soon afterwards it made a final pause, assured itself of its
error, and flew with the speed of the wind to its refuge in the
mountains.
FOOTNOTES:
[A] A painting of this exquisite lake has been recently executed by Mr.
George Barnard.
ASCENT OF THE FINSTERAARHORN, 1858.
(16.)
[Sidenote: MY GUIDE. 1858.]
Since my arrival at the hotel on the 30th of July I had once or twice
spoken about ascending the Finsteraarhorn, and on the 2nd of August my
host advised me to avail myself of the promising weather. A guide, named
Bennen, was attached to the hotel, a remarkable-looking man, between 30
and 40 years old, of middle stature, but very strongly built. His
countenance was frank and firm, while a light of good-nature at times
twinkled in his eye. Altogether the man gave me the impression of
physical strength, combined with decision of character. The proprietor
had spoken to me many times of the strength and courage of this man,
winding up his praises of him by the assurance that if I were killed in
Bennen's company there would be two lives lost, for that the guide would
assuredly sacrifice himself in the effort to save his _Herr_.
He was called, and I asked him whether he would accompany me alone to
the top of the Finsteraarhorn. To this he at first objected, urging the
possibility of his having to render me assistance, and the great amount
of labour which this might entail upon him; but this was overruled by my
engaging to follow where he led, without asking him to render me any
help whatever. He then agreed to make the trial, stipulating, however,
that he should not have much to carry to the cave of the Faulberg, where
we were to spend the night. To this I cordially agreed, and sent on
blankets, provisions, wood, and hay, by two porters.
[Sidenote: IRIDESCENT CLOUD. 1858.]
My desire, in part, was to make a series of observations at the summit
of the mountain, while a similar series was made by Professor Ramsay in
the valley of the Rhone, near Viesch, with a view to ascertaining the
permeability of the lower strata of the atmosphere to the radiant heat
of the sun. During the forenoon of the 2nd I occupied myself with my
instruments, and made the proper arrangements with Ramsay. I tested a
mountain-thermometer which Mr. Casella had kindly lent me, and found the
boiling point of water on the dining-room table of the hotel to be
199.29° Fahrenheit. At about three o'clock in the afternoon we quitted
the hotel, and proceeded leisurely with our two guides up the slope of
the Æggischhorn. We once caught a sight of the topmost pinnacle of the
Finsteraarhorn; beside it was the Rothhorn, and near this again the
Oberaarhorn, with the Viescher glacier streaming from its shoulders. On
the opposite side we could see, over an oblique buttress of the mountain
on which we stood, the snowy summit of the Weisshorn; to the left of
this was the ever grim and lonely Matterhorn; and farther to the left,
with its numerous snow-cones, each with its attendant shadow, rose the
mighty Mischabel. We descended, and crossed the stream which flows from
the Märjelen See, into which a large mass of the glacier had recently
fallen, and was now afloat as an iceberg. We passed along the margin of
the lake, and at the junction of water and ice I bade Ramsay good-bye.
At the commencement of our journey upon the ice, whenever we crossed a
crevasse, I noticed Bennen watching me; his vigilance, however, soon
diminished, whence I gathered that he finally concluded that I was able
to take care of myself. Clouds hovered in the atmosphere throughout the
whole time of our ascent; one smoky-looking mass marred the glory of the
sunset, but at some distance was another which exhibited colours almost
as rich and varied as those of the solar spectrum. I took the glorious
banner thus unfurled as a sign of hope, to check the despondency which
its gloomy neighbour was calculated to produce.
[Sidenote: EVENING NEAR THE JUNGFRAU. 1858.]
Two hours' walking brought us near our place of rest; the porters had
already reached it, and were now returning. We deviated to the right,
and, having crossed some ice-ravines, reached the lateral moraine of the
glacier, and picked our way between it and the adjacent mountain-wall.
We then reached a kind of amphitheatre, crossed it, and climbing the
opposite slope, came to a triple grotto formed by clefts in the
mountain. In one of these a pine-fire was soon blazing briskly, and
casting its red light upon the surrounding objects, though but half
dispelling the gloom from the deeper portions of the cell. I left the
grotto, and climbed the rocks above it to look at the heavens. The sun
had quitted our firmament, but still tinted the clouds with red and
purple; while one peak of snow in particular glowed like fire, so vivid
was its illumination. During our journey upwards the Jungfrau never once
showed her head, but, as if in ill temper, had wrapped her vapoury veil
around her. She now looked more good-humoured, but still she did not
quite remove her hood; though all the other summits, without a trace of
cloud to mask their beautiful forms, pointed heavenward. The calmness
was perfect; no sound of living creature, no whisper of a breeze, no
gurgle of water, no rustle of débris, to break the deep and solemn
silence. Surely, if beauty be an object of worship, those glorious
mountains, with rounded shoulders of the purest white--snow-crested and
star-gemmed--were well calculated to excite sentiments of adoration.
[Sidenote: THE CAVE OF THE FAULBERG. 1858.]
I returned to the grotto, where supper was prepared and waiting for me.
The boiling point of water, at the level of the "kitchen" floor, I found
to be 196° Fahr. Nothing could be more picturesque than the aspect of
the cave before we went to rest. The fire was gleaming ruddily. I sat
upon a stone bench beside it, while Bennen was in front with the red
light glimmering fitfully over him. My boiling-water apparatus, which
had just been used, was in the foreground; and telescopes,
opera-glasses, haversacks, wine-keg, bottles, and mattocks, lay
confusedly around. The heavens continued to grow clearer, the thin
clouds, which had partially overspread the sky, melting gradually away.
The grotto was comfortable; the hay sufficient materially to modify the
hardness of the rock, and my position at least sheltered and warm. One
possibility remained that might prevent me from sleeping--the snoring of
my companion; he assured me, however, that he did not snore, and we lay
down side by side. The good fellow took care that I should not be
chilled; he gave me the best place, by far the best part of the clothes,
and may have suffered himself in consequence; but, happily for him, he
was soon oblivious of this. Physiologists, I believe, have discovered
that it is chiefly during sleep that the muscles are repaired; and ere
long the sound I dreaded announced to me at once the repair of Bennen's
muscles and the doom of my own. The hollow cave resounded to the
deep-drawn snore. I once or twice stirred the sleeper, breaking thereby
the continuity of the phenomenon; but it instantly pieced itself
together again, and went on as before. I had not the heart to wake him,
for I knew that upon him would devolve the chief labour of the coming
day. At half-past one he rose and prepared coffee, and at two o'clock I
was engaged upon the beverage. We afterwards packed up our provisions
and instruments. Bennen bore the former, I the latter, and at three
o'clock we set out.
[Sidenote: "SHALL WE TRY THE JUNGFRAU?" 1858.]
We first descended a steep slope to the glacier, along which we walked
for a time. A spur of the Faulberg jutted out between us and the
ice-laden valley through which we must pass; this we crossed in order to
shorten our way and to avoid crevasses. Loose shingle and boulders
overlaid the mountain; and here and there walls of rock opposed our
progress, and rendered the route far from agreeable. We then descended
to the Grünhorn tributary, which joins the trunk glacier at nearly a
right angle, being terminated by a saddle which stretches across from
mountain to mountain, with a curvature as graceful and as perfect as if
drawn by the instrument of a mathematician. The unclouded moon was
shining, and the Jungfrau was before us so pure and beautiful, that the
thought of visiting the "Maiden" without further preparation occurred to
me. I turned to Bennen, and said, "Shall we try the Jungfrau?" I think
he liked the idea well enough, though he cautiously avoided incurring
any responsibility. "If you desire it, I am ready," was his reply. He
had never made the ascent, and nobody knew anything of the state of the
snow this year; but Lauener had examined it through a telescope on the
previous day, and pronounced it dangerous. In every ascent of the
mountain hitherto made, ladders had been found indispensable, but we had
none. I questioned Bennen as to what he thought of the probabilities,
and tried to extract some direct encouragement from him; but he said
that the decision rested altogether with myself, and it was his business
to endeavour to carry out that decision. "We will attempt it, then," I
said, and for some time we actually walked towards the Jungfrau. A gray
cloud drew itself across her summit, and clung there. I asked myself why
I deviated from my original intention? The Finsteraarhorn was higher,
and therefore better suited for the contemplated observations. I could
in no wise justify the change, and finally expressed my scruples. A
moment's further conversation caused us to "right about," and front the
saddle of the Grünhorn.
[Sidenote: MAGNIFICENT SCENE. 1858.]
The dawn advanced. The eastern sky became illuminated and warm, and high
in the air across the ridge in front of us stretched a tongue of cloud
like a red flame, and equally fervid in its hue. Looking across the
trunk glacier, a valley which is terminated by the Lötsch saddle was
seen in a straight line with our route, and I often turned to look along
this magnificent corridor. The mightiest mountains in the Oberland form
its sides; still, the impression which it makes is not that of vastness
or sublimity, but of loveliness not to be described. The sun had not yet
smitten the snows of the bounding mountains, but the saddle carved out a
segment of the heavens which formed a background of unspeakable beauty.
Over the rim of the saddle the sky was deep orange, passing upwards
through amber, yellow, and vague ethereal green to the ordinary
firmamental blue. Right above the snow-curve purple clouds hung
perfectly motionless, giving depth to the spaces between them. There was
something saintly in the scene. Anything more exquisite I had never
beheld.
We marched upwards over the smooth crisp snow to the crest of the
saddle, and here I turned to take a last look along that grand corridor,
and at that wonderful "daffodil sky." The sun's rays had already smitten
the snows of the Aletschhorn; the radiance seemed to infuse a principle
of life and activity into the mountains and glaciers, but still that
holy light shone forth, and those motionless clouds floated beyond,
reminding one of that eastern religion whose essence is the repression
of all action and the substitution for it of immortal calm. The
Finsteraarhorn now fronted us; but clouds turbaned the head of the
giant, and hid it from our view. The wind, however, being north,
inspired us with a strong hope that they would melt as the day advanced.
I have hardly seen a finer ice-field than that which now lay before us.
Considering the _névé_ which supplies it, it appeared to me that the
Viescher glacier ought to discharge as much ice as the Aletsch; but this
is an error due to the extent of _névé_ which is here at once visible:
since a glance at the map of this portion of the Oberland shows at once
the great superiority of the mountain treasury from which the Aletsch
glacier draws support. Still, the ice-field before us was a most noble
one. The surrounding mountains were of imposing magnitude, and loaded to
their summits with snow. Down the sides of some of them the
half-consolidated mass fell in a state of wild fracture and confusion.
In some cases the riven masses were twisted and overturned, the ledges
bent, and the detached blocks piled one upon another in heaps; while in
other cases the smooth white mass descended from crown to base without a
wrinkle. The valley now below us was gorged by the frozen material thus
incessantly poured into it. We crossed it, and reached the base of the
Finsteraarhorn, ascended the mountain a little way, and at six o'clock
paused to lighten our burdens and to refresh ourselves.
[Sidenote: THE MOUNTAIN ASSAILED. 1858.]
The north wind had freshened, we were in the shade, and the cold was
very keen. Placing a bottle of tea and a small quantity of provisions in
the knapsack, and a few figs and dried prunes in our pockets, we
commenced the ascent. The Finsteraarhorn sends down a number of cliffy
buttresses, separated from each other by wide couloirs filled with ice
and snow. We ascended one of these buttresses for a time, treading
cautiously among the spiky rocks; afterwards we went along the snow at
the edge of the spine, and then fairly parted company with the rock,
abandoning ourselves to the _névé_ of the couloir. The latter was steep,
and the snow was so firm that steps had to be cut in it. Once I paused
upon a little ledge, which gave me a slight footing, and took the
inclination. The slope formed an angle of 45° with the horizon; and
across it, at a little distance below me, a gloomy fissure opened its
jaws. The sun now cleared the summits which had before cut off his rays,
and burst upon us with great power, compelling us to resort to our
veils and dark spectacles. Two years before, Bennen had been nearly
blinded by inflammation brought on by the glare from the snow, and he
now took unusual care in protecting his eyes. The rocks looking more
practicable, we again made towards them, and clambered among them till a
vertical precipice, which proved impossible of ascent, fronted us.
Bennen scanned the obstacle closely as we slowly approached it, and
finally descended to the snow, which wound at a steep angle round its
base: on this the footing appeared to me to be singularly insecure, but
I marched without hesitation or anxiety in the footsteps of my guide.
[Sidenote: THE CREST OF ROCKS. 1858.]
We ascended the rocks once more, continued along them for some time, and
then deviated to the couloir on our left. This snow-slope is much
dislocated at its lower portion, and above its precipices and crevasses
our route now lay. The snow was smooth, and sufficiently firm and steep
to render the cutting of steps necessary. Bennen took the lead: to make
each step he swung his mattock once, and his hindmost foot rose exactly
at the moment the mattock descended; there was thus a kind of rhythm in
his motion, the raising of the foot keeping time to the swing of the
implement. In this manner we proceeded till we reached the base of the
rocky pyramid which caps the mountain.
[Sidenote: THE SUMMIT GAINED. 1858.]
One side of the pyramid had been sliced off, thus dropping down almost a
sheer precipice for some thousands of feet to the Finsteraar glacier. A
wall of rock, about 10 or 15 feet high, runs along the edge of the
mountain, and this sheltered us from the north wind, which surged with
the sound of waves against the tremendous barrier at the other side.
"Our hardest work is now before us," said my guide. Our way lay up the
steep and splintered rocks, among which we sought out the spikes which
were closely enough wedged to bear our weight. Each had to trust to
himself, and I fulfilled to the letter my engagement with Bennen to ask
no help. My boiling-water apparatus and telescope were on my back, much
to my annoyance, as the former was heavy, and sometimes swung awkwardly
round as I twisted myself among the cliffs. Bennen offered to take it,
but he had his own share to carry, and I was resolved to bear mine.
Sometimes the rocks alternated with spaces of ice and snow, which we
were at intervals compelled to cross; sometimes, when the slope was pure
ice and very steep, we were compelled to retreat to the highest cliffs.
The wall to which I have referred had given way in some places, and
through the gaps thus formed the wind rushed with a loud, wild, wailing
sound. Through these spaces I could see the entire field of Agassiz's
observations; the junction of the Lauteraar and Finsteraar glaciers at
the Abschwung, the medial moraine between them, on which stood the Hôtel
des Neufchâtelois, and the pavilion built by M. Dollfuss, in which
Huxley and myself had found shelter two years before. Bennen was
evidently anxious to reach the summit, and recommended all observations
to be postponed until after our success had been assured. I agreed to
this, and kept close at his heels. Strong as he was, he sometimes
paused, laid his head upon his mattock, and panted like a chased deer.
He complained of fearful thirst, and to quench it we had only my bottle
of tea: this we shared loyally, my guide praising its virtues, as well
he might. Still the summit loomed above us; still the angry swell of the
north wind, beating against the torn battlements of the mountain, made
wild music. Upward, however, we strained; and at last, on gaining the
crest of a rock, Bennen exclaimed, in a jubilant voice, "_Die höchste
Spitze!_"--the highest point. In a moment I was at his side, and saw the
summit within a few paces of us. A minute or two placed us upon the
topmost-pinnacle, with the blue dome of heaven above us, and a world of
mountains, clouds, and glaciers beneath.
A notion is entertained by many of the guides that if you go to sleep at
the summit of any of the highest mountains, you will
"Sleep the sleep that knows no waking."
[Sidenote: THERMOMETER PLACED. 1858.]
Bennen did not appear to entertain this superstition; and before
starting in the morning, I had stipulated for ten minutes' sleep on
reaching the summit, as part compensation for the loss of the night's
rest. My first act, after casting a glance over the glorious scene
beneath us, was to take advantage of this agreement; so I lay down and
had five minutes' sleep, from which I rose refreshed and brisk. The sun
at first beat down upon us with intense force, and I exposed my
thermometers; but thin veils of vapour soon drew themselves before the
sun, and denser mists spread over the valley of the Rhone, thus
destroying all possibility of concert between Ramsay and myself. I
turned therefore to my boiling-water apparatus, filled it with snow,
melted the first charge, put more in, and boiled it; ascertaining the
boiling point to be 187° Fahrenheit. On a sheltered ledge, about two or
three yards south of the highest point, I placed a minimum-thermometer,
in the hope that it would enable us in future years to record the lowest
winter temperatures at the summit of the mountain.[A]
[Sidenote: SCENE FROM THE SUMMIT. 1858.]
It is difficult to convey any just impression of the scene from the
summit of the Finsteraarhorn: one might, it is true, arrange the visible
mountains in a list, stating their heights and distances, and leaving
the imagination to furnish them with peaks and pinnacles, to build the
precipices, polish the snow, rend the glaciers, and cap the highest
summits with appropriate clouds. But if imagination did its best in this
way, it would hardly exceed the reality, and would certainly omit many
details which contribute to the grandeur of the scene itself. The
various shapes of the mountains, some grand, some beautiful, bathed in
yellow sunshine, or lying black and riven under the frown of impervious
cumuli; the pure white peaks, cornices, bosses, and amphitheatres; the
blue ice rifts, the stratified snow-precipices, the glaciers issuing
from the hollows of the eternal hills, and stretching like frozen
serpents through the sinuous valleys; the lower cloud field--itself an
empire of vaporous hills--shining with dazzling whiteness, while here
and there grim summits, brown by nature, and black by contrast, pierce
through it like volcanic islands through a shining sea,--add to this the
consciousness of one's position which clings to one _unconsciously_,
that undercurrent of emotion which surrounds the question of one's
personal safety, at a height of more than 14,000 feet above the sea, and
which is increased by the weird strange sound of the wind surging with
the full deep boom of the distant sea against the precipice behind, or
rising to higher cadences as it forces itself through the crannies of
the weatherworn rocks,--all conspire to render the scene from the
Finsteraarhorn worthy of the monarch of the Bernese Alps.
[Sidenote: "HAVE NO FEAR." 1858.]
[Sidenote: DISCIPLINE. 1858.]
My guide at length warned me that we must be moving; repeating the
warning more impressively before I attended to it. We packed up, and as
we stood beside each other ready to march he asked me whether we should
tie ourselves together, at the same time expressing his belief that it
was unnecessary. Up to this time we had been separate, and the thought
of attaching ourselves had not occurred to me till he mentioned it. I
thought it, however, prudent to accept the suggestion, and so we united
our destinies by a strong rope. "Now," said Bennen, "have no fear; no
matter how you throw yourself, I will hold you." Afterwards, on another
perilous summit, I repeated this saying of Bennen's to a strong and
active guide, but his observation was that it was a hardy untruth, for
that in many places Bennen could not have held me. Nevertheless a daring
word strengthens the heart, and, though I felt no trace of that
sentiment which Bennen exhorted me to banish, and was determined, as far
as in me lay, to give him no opportunity of trying his strength in
saving me, I liked the fearless utterance of the man, and sprang
cheerily after him. Our descent was rapid, apparently reckless, amid
loose spikes, boulders, and vertical prisms of rock, where a false step
would assuredly have been attended with broken bones; but the
consciousness of certainty in our movements never forsook us, and proved
a source of keen enjoyment. The senses were all awake, the eye clear,
the heart strong, the limbs steady, yet flexible, with power of recovery
in store, and ready for instant action should the footing give way. Such
is the discipline which a perilous ascent imposes.
[Sidenote: DESCENT BY GLISSADES. 1858.]
We finally quitted the crest of rocks, and got fairly upon the snow once
more. We first went downwards at a long swinging trot. The sun having
melted the crust which we were compelled to cut through in the morning,
the leg at each plunge sank deeply into the snow; but this sinking was
partly in the direction of the slope of the mountain, and hence assisted
our progress. Sometimes the crust was hard enough to enable us to glide
upon it for long distances while standing erect; but the end of these
_glissades_ was always a plunge and tumble in the deeper snow. Once upon
a steep hard slope Bennen's footing gave way; he fell, and went down
rapidly, pulling me after him. I fell also, but turning quickly, drove
the spike of my hatchet into the ice, got good anchorage, and held both
fast; my success assuring me that I had improved as a mountaineer since
my ascent of Mont Blanc. We tumbled so often in the soft snow, and our
clothes and boots were so full of it, that we thought we might as well
try the sitting posture in gliding down. We did so, and descended with
extraordinary velocity, being checked at intervals by a bodily immersion
in the softer and deeper snow. I was usually in front of Bennen,
shooting down with the speed of an arrow and feeling the check of the
rope when the rapidity of my motion exceeded my guide's estimate of
what was safe. Sometimes I was behind him, and darted at intervals with
the swiftness of an avalanche right upon him; sometimes in the same
transverse line with him, with the full length of the rope between us;
and here I found its check unpleasant, as it tended to make me roll
over. My feet were usually in the air, and it was only necessary to turn
them right or left, like the helm of a boat, to change the direction of
motion and avoid a difficulty, while a vigorous dig of leg and hatchet
into the snow was sufficient to check the motion and bring us to rest.
Swiftly, yet cautiously, we glided into the region of crevasses, where
we at last rose, quite wet, and resumed our walking, until we reached
the point where we had left our wine in the morning, and where I
squeezed the water from my wet clothes, and partially dried them in the
sun.
[Sidenote: THE VIESCH GLACIER. 1858.]
We had left some things at the cave of the Faulberg, and it was Bennen's
first intention to return that way and take them home with him. Finding,
however, that we could traverse the Viescher glacier almost to the
Æggischhorn, I made this our highway homewards. At the place where we
entered it, and for an hour or two afterwards, the glacier was cut by
fissures, for the most part covered with snow. We had packed up our
rope, and Bennen admonished me to tread in his steps. Three or four
times he half disappeared in the concealed fissures, but by clutching
the snow he rescued himself and went on as swiftly as before. Once my
leg sank, and the ring of icicles some fifty feet below told me that I
was in the jaws of a crevasse; my guide turned sharply--it was the only
time that I had seen concern on his countenance:--
"_Gott's Donner! Sie haben meine Tritte nicht gefolgt._"
"_Doch!_" was my only reply, and we went on. He scarcely tried the snow
that he crossed, as from its form and colour he could in most cases
judge of its condition. For a long time we kept at the left-hand side of
the glacier, avoiding the fissures which were now permanently open. We
came upon the tracks of a herd of chamois, which had clambered from the
glacier up the sides of the Oberaarhorn, and afterwards crossed the
glacier to the right-hand side, my guide being perfect master of the
ground. His eyes went in advance of his steps, and his judgment was
formed before his legs moved. The glacier was deeply fissured, but there
was no swerving, no retreating, no turning back to seek more practicable
routes; each stride told, and every stroke of the axe was a profitable
investment of labour.
We left the glacier for a time, and proceeded along the mountain side,
till we came near the end of the Trift glacier, where we let ourselves
down an awkward face of rock along the track of a little cascade, and
came upon the glacier once more. Here again I had occasion to admire the
knowledge and promptness of my guide. The glacier, as is well known, is
greatly dislocated, and has once or twice proved a prison to guides and
travellers, but Bennen led me through the confusion without a pause. We
were sometimes in the middle of the glacier, sometimes on the moraine,
and sometimes on the side of the flanking mountain. Towards the end of
the day we crossed what seemed to be the consolidated remains of a great
avalanche; on this my foot slipped, there was a crevasse at hand, and a
sudden effort was necessary to save me from falling into it. In making
this effort the spike of my axe turned uppermost, and the palm of my
hand came down upon it, thus receiving a very ugly wound. We were soon
upon the green alp, having bidden a last farewell to the ice. Another
hour's hard walking brought us to our hotel. No one seeing us crossing
the alp would have supposed that we had laid such a day's work behind
us; the proximity of home gave vigour to our strides, and our progress
was much more speedy than it had been on starting in the morning. I was
affectionately welcomed by Ramsay, had a warm bath, dined, went to bed,
where I lay fast locked in sleep for eight hours, and rose next morning
as fresh and vigorous as if I had never scaled the Finsteraarhorn.
FOOTNOTES:
[A] The following note describes the single observation made with this
thermometer. Mr. B. informs me that on finding the instrument Bennen
swung it in triumph round his head. I fear, therefore, that the
observation gives us no certain information regarding the minimum
winter-temperature.
"St. Nicholas, 1859, Aug. 25.
"Sir,--On Tuesday last (the 23rd inst.) a party, consisting of Messrs.
B., H., R. L., and myself, succeeded in reaching the summit of the
Finsteraarhorn under the guidance of Bennen and Melchior Anderegg. We
made it an especial object to observe and reset the minimum-thermometer
which you left there last year. On reaching the summit, before I had
time to stop him, Bennen produced the instrument, and it is just
possible that in moving it he may have altered the position of the
index. However, as he held the instrument horizontally, and did not, as
far as I saw, give it any sensible jerk, I have great confidence that
the index remained unmoved.
"The reading of the index was -32° Cent.
"A portion of the spirit extending over about 10-1/2° (and standing
tween 33° and 43-1/2°) was separated from the rest, but there appeared
to be no data for determining when the separation had taken place. As it
appeared desirable to unite the two portions of spirit before again
setting the index to record the cold of another winter, we endeavoured
to effect this by heating the bulb, but unfortunately, just as we were
expecting to see them coalesce, the bulb burst, and I have now to
express my great regret that my clumsiness or ignorance of the proper
mode of setting the instrument in order should have interfered with the
continuance of observations of so much interest. The remains of the
instrument, together with a note of the accident, I have left in the
charge of Wellig, the landlord of the hotel on the Æggischhorn.
"We reached the summit about 10.40 A.M. and remained there till noon;
the reading of a pocket thermometer in the shade was 41° F.
"Should there be any further details connected with our ascent on which
you would like to have information, I shall be happy to supply them to
the best of my recollection. Meanwhile, with a farther apology for my
clumsiness, I beg to subscribe myself yours respectfully,
"H."
"Professor Tyndall."
(17.)
[Sidenote: A ROTATING ICEBERG. 1858.]
On the 6th of August there was a long fight between mist and sunshine,
each triumphing by turns, till at length the orb gained the victory and
cleansed the mountains from every trace of fog. We descended to the
Märjelen See, and, wishing to try the floating power of its icebergs, at
a place where masses sufficiently large approached near to the shore, I
put aside a portion of my clothes, and retaining my boots stepped upon
the floating ice. It bore me for a time, and I hoped eventually to be
able to paddle myself over the water. On swerving a little, however,
from the position in which I first stood, the mass turned over and let
me into the lake. I tried a second one, which served me in the same
manner; the water was too cold to continue the attempt, and there was
also some risk of being unpleasantly ground between the opposing
surfaces of the masses of ice. A very large iceberg which had been
detached some short time previously from the glacier lay floating at
some distance from us. Suddenly a sound like that of a waterfall drew
our attention towards it. We saw it roll over with the utmost
deliberation, while the water which it carried along with it rushed in
cataracts down its sides. Its previous surface was white, its present
one was of a lovely blue, the submerged crystal having now come to the
air. The summerset of this iceberg produced a commotion all over the
lake; the floating masses at its edge clashed together, and a mellow
glucking sound, due to the lapping of the undulations against the frozen
masses, continued long afterwards.
We subsequently spent several hours upon the glacier; and on this day I
noticed for the first time a contemporaneous exhibition of _bedding_ and
_structure_ to which I shall refer at another place. We passed finally
to the left bank of the glacier, at some distance below the base of the
Æggischhorn, and traced its old moraines at intervals along the flanks
of the bounding mountain. At the summit of the ridge we found several
fine old _roches moutonnées_, on some of which the scratchings of a
glacier long departed were well preserved; and from the direction of the
scratchings it might be inferred that the ice moved down the mountain
towards the valley of the Rhone. A plunge into a lonely mountain lake
ended the day's excursion.
[Sidenote: END OF THE ALETSCH GLACIER. 1858.]
On the 7th of August we quitted this noble station. Sending our guide on
to Viesch to take a conveyance and proceed with our luggage down the
valley, Ramsay and myself crossed the mountains obliquely, desiring to
trace the glacier to its termination. We had no path, but it was hardly
possible to go astray. We crossed spurs, climbed and descended pleasant
mounds, sometimes with the soft grass under our feet, and sometimes
knee-deep in rhododendrons. It took us several hours to reach the end of
the glacier, and we then looked down upon it merely. It lay couched like
a reptile in a wild gorge, as if it had split the mountain by its frozen
snout. We afterwards descended to Mörill, where we met our guide and
driver; thence down the valley to Visp; and the following evening saw us
lodged at the Monte Rosa hotel in Zermatt.
The boiling point of water on the table of the _salle à manger_, I found
to be 202.58° Fahr.
[Sidenote: MEADOWS INVADED BY ICE. 1858.]
On the following morning I proceeded without my friend to the Görner
glacier. As is well known, the end of this glacier has been steadily
advancing for several years, and when I saw it, the meadow in front of
it was partly shrivelled up by its irresistible advance. I was informed
by my host that within the last sixty years forty-four chalets had been
overturned by the glacier, the ground on which they stood being occupied
by the ice; at present there are others for which a similar fate seems
imminent. In thus advancing the glacier merely takes up ground which
belonged to it in former ages, for the rounded rocks which rise out of
the adjacent meadow show that it once passed over them.
I had arranged to meet Ramsay this morning on the road to the
Riffelberg. The meeting took place, but I then learned that a minute or
two after my departure he had received intelligence of the death of a
near relative. Thus was our joint expedition terminated, for he resolved
to return at once to England. At my solicitation he accompanied me to
the Riffel hotel. We had planned an ascent of Monte Rosa together, but
the arrangement thus broke down, and I was consequently thrown upon my
own resources. Lauener had never made the ascent, but he nevertheless
felt confident that we should accomplish it together.
FIRST ASCENT OF MONTE ROSA, 1858.
(18.)
[Sidenote: THE RIFFELBERG. 1858.]
[Sidenote: SOUNDS ON THE GLACIER. 1858.]
On Monday, the 9th of August, we reached the Riffel, and, by good
fortune, on the evening of the same day, my guide's brother, the
well-known Ulrich Lauener, also arrived at the hotel on his return from
Monte Rosa. From him we obtained all the information possible respecting
the ascent, and he kindly agreed to accompany us a little way the next
morning, to put us on the right track. At three A.M. the door of my
bedroom opened, and Christian Lauener announced to me that the weather
was sufficiently good to justify an attempt. The stars were shining
overhead; but Ulrich afterwards drew our attention to some heavy clouds
which clung to the mountains on the other side of the valley of the
Visp; remarking that the weather _might_ continue fair throughout the
day, but that these clouds were ominous. At four o'clock we were on our
way, by which time a gray stratus cloud had drawn itself across the neck
of the Matterhorn, and soon afterwards another of the same nature
encircled his waist. We proceeded past the Riffelhorn to the ridge above
the Görner glacier, from which Monte Rosa was visible from top to
bottom, and where an animated conversation in Swiss patois commenced.
Ulrich described the slopes, passes, and precipices, which were to guide
us; and Christian demanded explanations, until he was finally able to
declare to me that his knowledge was sufficient. We then bade Ulrich
good-bye, and went forward. All was clear about Monte Rosa, and the
yellow morning light shone brightly upon its uppermost snows. Beside the
Queen of the Alps was the huge mass of the Lyskamm, with a saddle
stretching from the one to the other; next to the Lyskamm came two
white rounded mounds, smooth and pure, the Twins Castor and Pollux, and
further to the right again the broad brown flank of the Breithorn.
Behind us Mont Cervin gathered the clouds more thickly round him, until
finally his grand obelisk was totally hidden. We went along the
mountain-side for a time, and then descended to the glacier. The surface
was hard frozen, and the ice crunched loudly under our feet. There was a
hollowness and volume in the sound which require explanation; and this,
I think, is furnished by the remarks of Sir John Herschel on those
hollow sounds at the Solfaterra, near Naples, from which travellers have
inferred the existence of cavities within the mountain. At the place
where these sounds are heard the earth is friable, and, when struck, the
concussion is reinforced and lengthened by the partial echoes from the
surfaces of the fragments. The conditions for a similar effect exist
upon the glacier, for the ice is disintegrated to a certain depth, and
from the innumerable places of rupture little reverberations are sent,
which give a length and hollowness to the sound produced by the crushing
of the fragments on the surface.
We looked to the sky at intervals, and once a meteor slid across it,
leaving a train of sparks behind. The blue firmament, from which the
stars shone down so brightly when we rose, was more and more invaded by
clouds, which advanced upon us from our rear, while before us the solemn
heights of Monte Rosa were bathed in rich yellow sunlight. As the day
advanced the radiance crept down towards the valleys; but still those
stealthy clouds advanced like a besieging army, taking deliberate
possession of the summits, one after the other, while gray skirmishers
moved through the air above us. The play of light and shadow upon Monte
Rosa was at times beautiful, bars of gloom and zones of glory shifting
and alternating from top to bottom of the mountain.
[Sidenote: ADVANCE OF THE CLOUDS. 1858.]
At five o'clock a gray cloud alighted on the shoulder of the Lyskamm,
which had hitherto been warmed by the lovely yellow light. Soon
afterwards we reached the foot of Monte Rosa, and passed from the
glacier to a slope of rocks, whose rounded forms and furrowed surfaces
showed that the ice of former ages had moved over them; the granite was
now coated with lichens, and between the bosses where mould could rest
were patches of tender moss. As we ascended, a peal to the right
announced the descent of an avalanche from the Twins; it came heralded
by clouds of ice-dust, which resembled the sphered masses of condensed
vapour which issue from a locomotive. A gentle snow-slope brought us to
the base of a precipice of brown rocks, round which we wound; the snow
was in excellent order, and the chasms were so firmly bridged by the
frozen mass that no caution was necessary in crossing them. Surmounting
a weathered cliff to our left, we paused upon the summit to look upon
the scene around us. The snow gliding insensibly from the mountains, or
discharged in avalanches from the precipices which it overhung, filled
the higher valleys with pure white glaciers, which were rifted and
broken here and there, exposing chasms and precipices from which gleamed
the delicate blue of the half-formed ice. Sometimes, however, the
_névés_ spread over wide spaces without a rupture or wrinkle to break
the smoothness of the superficial snow. The sky was now for the most
part overcast, but through the residual blue spaces the sun at intervals
poured light over the rounded bosses of the mountain.
[Sidenote: MONTE ROSA CAPPED. 1858.]
At half-past seven o'clock we reached another precipice of rock, to the
left of which our route lay, and here Lauener proposed to have some
refreshment; after which we went on again. The clouds spread more and
more, leaving at length mere specks and patches of blue between them.
Passing some high peaks, formed by the dislocation of the ice, we came
to a place where the _névé_ was rent by crevasses, on the walls of which
the stratification due to successive snow-falls was shown with great
beauty and definition. Between two of these fissures our way now lay:
the wall of one of them was hollowed out longitudinally midway down,
thus forming a roof above and a ledge below, and from roof to ledge
stretched a railing of cylindrical icicles, as if intended to bolt them
together. A cloud now for the first time touched the summit of Monte
Rosa, and sought to cling to it, but in a minute it dispersed in
shattered fragments, as if dashed to pieces for its presumption. The
mountain remained for a time clear and triumphant, but the triumph was
short-lived: like suitors that will not be repelled, the dusky vapours
came; repulse after repulse took place, and the sunlight gushed down
upon the heights, but it was manifest that the clouds gained ground in
the conflict.
Until about a quarter past nine o'clock our work was mere child's play,
a pleasant morning stroll along the flanks of the mountain; but steeper
slopes now rose above us, which called for more energy, and more care in
the fixing of the feet. Looked at from below, some of these slopes
appeared precipitous; but we were too well acquainted with the effect of
fore-shortening to let this daunt us. At each step we dug our bâtons
into the deep snow. When first driven in, the bâtons[A] _dipped_ from
us, but were brought, as we walked forward, to the vertical, and finally
beyond it at the other side. The snow was thus forced aside, a rubbing
of the staff against it, and of the snow-particles against each other,
being the consequence. We had thus perpetual rupture and regelation;
while the little sounds consequent upon rupture, reinforced by the
partial echoes from the surfaces of the granules, were blended together
to a note resembling the lowing of cows. Hitherto I had paused at
intervals to make notes, or to take an angle; but these operations now
ceased, not from want of time, but from pure dislike; for when the eye
has to act the part of a sentinel who feels that at any moment the enemy
may be upon him; when the body must be balanced with precision, and legs
and arms, besides performing actual labour, must be kept in readiness
for possible contingencies; above all, when you feel that your safety
depends upon yourself alone, and that, if your footing gives way, there
is no strong arm behind ready to be thrown between you and destruction;
under such circumstances the relish for writing ceases, and you are
willing to hand over your impressions to the safe keeping of memory.
[Sidenote: THE "COMB" OF THE MOUNTAIN. 1858.]
[Sidenote: ASCENT ALONG A CORNICE. 1858.]
From the vast boss which constitutes the lower portion of Monte Rosa
cliffy edges run upwards to the summit. Were the snow removed from these
we should, I doubt not, see them as toothed or serrated crags,
justifying the term "_kamm_," or "comb," applied to such edges by the
Germans. Our way now lay along such a kamm, the cliffs of which had,
however, caught the snow, and been completely covered by it, forming an
edge like the ridge of a house-roof, which sloped steeply upwards. On
the Lyskamm side of the edge there was no footing, and, if a human body
fell over here, it would probably pass through a vertical space of some
thousands of feet, falling or rolling, before coming to rest. On the
other side the snow-slope was less steep, but excessively
perilous-looking, and intersected by precipices of ice. Dense clouds now
enveloped us, and made our position far uglier than if it had been
fairly illuminated. The valley below us was one vast cauldron, filled
with precipitated vapour, which came seething at times up the sides of
the mountain. Sometimes this fog would partially clear away, and the
light would gleam upwards from the dislocated glaciers. My guide
continually admonished me to make my footing sure, and to fix at each
step my staff firmly in the consolidated snow. At one place, for a short
steep ascent, the slope became hard ice, and our position a very
ticklish one. We hewed our steps as we moved upwards, but were soon glad
to deviate from the ice to a position scarcely less awkward. The wind
had so acted upon the snow as to fold it over the edge of the kamm, thus
causing it to form a kind of cornice, which overhung the precipice on
the Lyskamm side of the mountain. This cornice now bore our weight: its
snow had become somewhat firm, but it was yielding enough to permit the
feet to sink in it a little way, and thus secure us at least against the
danger of slipping. Here also at each step we drove our bâtons firmly
into the snow, availing ourselves of whatever help they could render.
Once, while thus securing my anchorage, the handle of my hatchet went
right through the cornice on which we stood, and, on withdrawing it, I
could see through the aperture into the cloud-crammed gulf below. We
continued ascending until we reached a rock protruding from the snow,
and here we halted for a few minutes. Lauener looked upwards through the
fog. "According to all description," he observed, "this ought to be the
last kamm of the mountain; but in this obscurity we can see nothing."
Snow began to fall, and we recommenced our journey, quitting the rocks
and climbing again along the edge. Another hour brought us to a crest of
cliffs, at which, to our comfort, the kamm appeared to cease, and other
climbing qualities were demanded of us.
[Sidenote: "DIE HÖCHSTE SPITZE." 1858.]
On the Lyskamm side, as I have said, rescue would be out of the
question, should the climber go over the edge. On the other side of the
edge rescue seemed possible, though the slope, as stated already, was
most dangerously steep. I now asked Lauener what he would have done,
supposing my footing to have failed on the latter slope. He did not
seem to like the question, but said that he should have considered well
for a moment and then have sprung after me; but he exhorted me to drive
all such thoughts away. I laughed at him, and this did more to set his
mind at rest than any formal profession of courage could have done. We
were now among rocks: we climbed cliffs and descended them, and advanced
sometimes with our feet on narrow ledges, holding tightly on to other
ledges by our fingers; sometimes, cautiously balanced, we moved along
edges of rock with precipices on both sides. Once, in getting round a
crag, Lauener shook a book from his pocket; it was arrested by a rock
about sixty or eighty feet below us. He wished to regain it, but I
offered to supply its place, if he thought the descent too dangerous. He
said he would make the trial, and parted from me. I thought it useless
to remain idle. A cleft was before me, through which I must pass; so,
pressing my knees and back against its opposite sides, I gradually
worked myself to the top. I descended the other face of the rock, and
then, through a second ragged fissure, to the summit of another
pinnacle. The highest point of the mountain was now at hand, separated
from me merely by a short saddle, carved by weathering out of the crest
of the mountain. I could hear Lauener clattering after me, through the
rocks behind. I dropped down upon the saddle, crossed it, climbed the
opposite cliff, and "_die höchste Spitze_" of Monte Rosa was won.
[Sidenote: GLOOM ON THE SUMMIT. 1858.]
Lauener joined me immediately, and we mutually congratulated each other
on the success of the ascent. The residue of the bread and meat was
produced, and a bottle of tea was also appealed to. Mixed with a little
cognac, Lauener declared that he had never tasted anything like it. Snow
fell thickly at intervals, and the obscurity was very great;
occasionally this would lighten and permit the sun to shed a ghastly
dilute light upon us through the gleaming vapour. I put my
boiling-water apparatus in order, and fixed it in a corner behind a
ledge; the shelter was, however, insufficient, so I placed my hat above
the vessel. The boiling point was 184.92° Fahr., the ledge on which the
instrument stood being 5 feet below the highest point of the mountain.
The ascent from the Riffel hotel occupied us about seven hours, nearly
two of which were spent upon the kamm and crest. Neither of us felt in
the least degree fatigued; I, indeed, felt so fresh, that had another
Monte Rosa been planted on the first, I should have continued the climb
without hesitation, and with strong hopes of reaching the top. I
experienced no trace of mountain sickness, lassitude, shortness of
breath, heart-beat, or headache; nevertheless the summit of Monte Rosa
is 15,284 feet high, being less than 500 feet lower than Mont Blanc. It
is, I think, perfectly certain, that the rarefaction of the air at this
height is not sufficient of itself to produce the symptoms referred to;
physical exertion must be superadded.
[Sidenote: "FROZEN FLOWERS." 1858.]
After a few fitful efforts to dispel the gloom, the sun resigned the
dominion to the dense fog and the descending snow, which now prevented
our seeing more than 15 or 20 paces in any direction. The temperature of
the crags at the summit, which had been shone upon by the unclouded sun
during the earlier portion of the day, was 60° Fahr.; hence the snow
melted instantly wherever it came in contact with the rock. But some of
it fell upon my felt hat, which had been placed to shelter the
boiling-water apparatus, and this presented the most remarkable and
beautiful appearance. The fall of snow was in fact a shower of frozen
flowers. All of them were six-leaved; some of the leaves threw out
lateral ribs like ferns, some were rounded, others arrowy and serrated,
some were close, others reticulated, but there was no deviation from the
six-leaved type. Nature seemed determined to make us some compensation
for the loss of all prospect, and thus showered down upon us those
lovely blossoms of the frost; and had a spirit of the mountain inquired
my choice, the view, or the frozen flowers, I should have hesitated
before giving up that exquisite vegetation. It was wonderful to think
of, as well as beautiful to behold. Let us imagine the eye gifted with a
microscopic power sufficient to enable it to see the molecules which
composed these starry crystals; to observe the solid nucleus formed and
floating in the air; to see it drawing towards it its allied atoms, and
these arranging themselves as if they moved to music, and ended by
rendering that music concrete. Surely such an exhibition of power, such
an apparent demonstration of a resident intelligence in what we are
accustomed to call "brute matter," would appear perfectly miraculous.
And yet the reality would, if we could see it, transcend the fancy. If
the Houses of Parliament were built up by the forces resident in their
own bricks and lithologic blocks, and without the aid of hodman or
mason, there would be nothing intrinsically more wonderful in the
process than in the molecular architecture which delighted us upon the
summit of Monte Rosa.
[Sidenote: STARTLING AVALANCHE. 1858.]
Twice or thrice had my guide warned me that we must think of descending,
for the snow continued to fall heavily, and the loss of our track would
be attended with imminent peril. We therefore packed up, and clambered
downward among the crags of the summit. We soon left these behind us,
and as we stood once more upon the kamm, looking into the gloom beneath,
an avalanche let loose from the side of an adjacent mountain shook the
air with its thunder. We could not see it, could form no estimate of its
distance, could only hear its roar, which coming to us through the
darkness, had an undefinable element of horror in it. Lauener remarked,
"I never hear those things without a shudder; the memory of my brother
comes back to me at the same time." His brother, who was the best
climber in the Oberland, had been literally broken to fragments by an
avalanche on the slopes of the Jungfrau.
We had been separate coming up, each having trusted to himself, but the
descent was more perilous, because it is more difficult to fix the heel
of the boot than the toe securely in the ice. Lauener was furnished with
a rope, which he now tied round my waist, and forming a noose at the
other end, he slipped it over his arm. This to me was a new mode of
attachment. Hitherto my guides in dangerous places had tied the ropes
round _their_ waists also. Simond had done it on Mont Blanc, and Bennen
on the Finsteraarhorn, proving thus their willingness to share my fate
whatever that might be. But here Lauener had the power of sending me
adrift at any moment, should his own life be imperilled. I told him that
his mode of attachment was new to me, but he assured me that it would
give him more power in case of accident. I did not see this at the time;
but neither did I insist on his attaching himself in the usual way. It
could neither be called anger nor pride, but a warm flush ran through me
as I remarked, that I should take good care not to test his power of
holding me. I believe I wronged my guide by the supposition that he made
the arrangement with reference to his own safety, for all I saw of him
afterwards proved that he would at any time have risked his life to save
mine. The flush however did me good, by displacing every trace of
anxiety, and the rope, I confess, was also a source of some comfort to
me. We descended the kamm, I going first. "Secure your footing before
you move," was my guide's constant exhortation, "and make your staff
firm at each step." We were sometimes quite close upon the rim of the
kamm on the Lyskamm side, and we also followed the depressions which
marked our track along the cornice. This I now tried intentionally, and
drove the handle of my axe through it once or twice. At two places in
descending we were upon the solid ice, and these were some of the
steepest portions of the kamm. They were undoubtedly perilous, and the
utmost caution was necessary in fixing the staff and securing the
footing. These however once past, we felt that the chief danger was
over. We reached the termination of the edge, and although the snow
continued to fall heavily, and obscure everything, we knew that our
progress afterwards was secure. There was pleasure in this feeling; it
was an agreeable variation of that grim mental tension to which I had
been previously wound up, but which in itself was by no means
disagreeable.
[Sidenote: SPLENDID BLUE OF THE SNOW. 1858.]
[Sidenote: STIFLING HEAT. 1858.]
I have already noticed the colour of the fresh snow upon the summit of
the Stelvio pass. Since I observed it there it has been my custom to pay
some attention to this point at all great elevations. This morning, as I
ascended Monte Rosa, I often examined the holes made in the snow by our
bâtons, but the light which issued from them was scarcely perceptibly
blue. Now, however, a deep layer of fresh snow overspread the mountain,
and the effect was magnificent. Along the kamm I was continually
surprised and delighted by the blue gleams which issued from the broken
or perforated stratum of new snow; each hole made by the staff was
filled with a light as pure, and nearly as deep, as that of the
unclouded firmament. When we reached the bottom of the kamm, Lauener
came to the front, and tramped before me. As his feet rose out of the
snow, and shook the latter off in fragments, sudden and wonderful gleams
of blue light flashed from them. Doubtless the blue of the sky has much
to do with mountain colouring, but in the present instance not only was
there no blue sky, but the air was so thick with fog and descending
snow-flakes, that we could not see twenty yards in advance of us. A
thick fog, which wrapped the mountain quite closely, now added its gloom
to the obscurity caused by the falling snow. Before we reached the base
of the mountain the fog became thin, and the sun shone through it. There
was not a breath of air stirring, and, though we stood ankle-deep in
snow, the heat surpassed anything of the kind I had ever felt: it was
the dead suffocating warmth of the interior of an oven, which
encompassed us on all sides, and from which there seemed no escape. Our
own motion through the air, however, cooled us considerably. We found
the snow-bridges softer than in the morning, and consequently needing
more caution; but we encountered no real difficulty among them. Indeed
it is amusing to observe the indifference with which a snow-roof is
often broken through, and a traveller immersed to the waist in the jaws
of a fissure. The effort at recovery is instantaneous; half
instinctively hands and knees are driven into the snow, and rescue is
immediate. Fair glacier work was now before us; after which we reached
the opposite mountain-slope, which we ascended, and then went down the
flank of the Riffelberg to our hotel. The excursion occupied us eleven
and a half hours.
FOOTNOTES:
[A] My staff was always the handle of an axe an inch or two longer than
an ordinary walking-stick.
(19.)
On the afternoon of the 11th I made an attempt alone to ascend the
Riffelhorn, and attained a considerable height; but I attacked it from
the wrong side, and the fading light forced me to retreat. I found some
agreeable people at the hotel on my return. One clergyman especially,
with a clear complexion, good digestion, and bad lungs--of free, hearty,
and genial manner--made himself extremely pleasant to us all. He
appeared to bubble over with enjoyment, and with him and others on the
morning of the 13th I walked to the Görner Grat, as it lay on the way to
my work. We had a glorious prospect from the summit: indeed the
assemblage of mountains, snow, and ice, here within view is perhaps
without a rival in the world.[A] I shouldered my axe, and saying
"good-bye" moved away from my companions.
"Are you going?" exclaimed the clergyman. "Give me one grasp of your
hand before we part."
This was the signal for a grasp all round; and the hearty human kindness
which thus showed itself contributed that day to make my work pleasant
to me.
[Sidenote: A DIFFICULT DESCENT. 1858.]
We proceeded along the ridge of the Rothe Kumme to a point which
commanded a fine view of the glacier. The ice had been over these
heights in ages past, for, although lichens covered the surfaces of the
old rocks, they did not disguise the grooves and scratchings. The
surface of the glacier was now about a thousand feet below us, and this
it was our desire to attain. To reach it we had to descend a succession
of precipices, which in general were weathered and rugged, but here and
there, where the rock was durable, were fluted and grooved. Once or
twice indeed we had nothing to cling to but the little ridges thus
formed. We had to squeeze ourselves through narrow fissures, and often
to get round overhanging ledges, where our main trust was in our feet,
but where these had only ledges an inch or so in width to rest upon.
These cases were to me the most unpleasant of all, for they compelled
the arms to take a position which, if the footing gave way, would
necessitate a _wrench_, for which I entertain considerable abhorrence.
We came at length to a gorge by which the mountain is rent from top to
bottom, and into which we endeavoured to descend. We worked along its
rim for a time, but found its smooth faces too deep. We retreated;
Lauener struck into another track, and while he tested it I sat down
near some grass tufts, which flourished on one of the ledges, and found
the temperature to be as follows:--
Temperature of rock 42° C.
Of air an inch above the rock 32
Of air a foot from rock 22
Of grass 25
The first of these numbers does not fairly represent the temperature of
the rock, as the thermometer could be in contact with it only at one
side at a time. It was differences such as these between grass and
stone, producing a mixed atmosphere of different densities, that
weakened the sound of the falls of the Orinoco, as observed and
explained by Humboldt.
[Sidenote: SINGULAR ICE-CAVE. 1858.]
By a process of "trial and error" we at length reached the ice, after
two hours had been spent in the effort to disentangle ourselves from the
crags. The glacier is forcibly thrust at this place against the
projecting base of the mountain, and the structure of the ice
correspondingly developed. Crevasses also intersect the ice, and the
blue veins cross them at right angles. I ascended the glacier to a
region where the ice was compressed and greatly contorted, and thought
that in some cases I could see the veins crossing the lines of
stratification. Once my guide drew my attention to what he called "_ein
sonderbares Loch_." On one of the slopes an archway was formed which
appeared to lead into the body of the glacier. We entered it, and
explored the cavern to its end. The walls were of transparent blue ice,
singularly free from air-bubbles; but where the roof of the cavern was
thin enough to allow the sun to shine feebly through it, the transmitted
light was of a pink colour. My guide expressed himself surprised at
"_den röthlichen Schein_." At one place a plate of ice had been placed
like a ceiling across the cavern; but owing to lateral squeezing it had
been broken so as to form a V. I found some air-bubbles in this ice, and
in all cases they were associated with blebs of water. A portion of the
"ceiling," indeed, was very full of bubbles, and was at some places
reduced, by internal liquefaction, to a mere skeleton of ice, with
water-cells between its walls.
[Sidenote: STRUCTURE AND STRATA. 1858.]
High up the glacier (towards the old Weissthor) the horizontal
stratification is everywhere beautifully shown. I drew my guide's
attention to it, and he made the remark that the perfection of the lower
ice was due to the pressure of the layers above it. "The snow by degrees
compressed itself to glacier." As we approached one of the tributaries
on the Monte Rosa side, where great pressure came into play, the
stratification appeared to yield and the true structure to cross it at
those places where it had yielded most. As the place of greatest
pressure was approached, the bedding disappeared more and more, and a
clear vertical structure was finally revealed.
FOOTNOTES:
[A] In 1858 Mr. E. W. Cooke made a pencil-sketch of this splendid
panorama, which is the best and truest that I have yet seen.
THE GÖRNER GRAT AND THE RIFFELHORN. MAGNETIC PHENOMENA.
(20.)
At an early hour on Saturday, the 14th of August, I heard the servant
exclaim, "_Das Wetter ist wunderschön!_" which good news caused me to
spring from my bed and prepare to meet the morn. The range of summits at
the opposite side of the valley of St. Nicholas was at first quite
clear, but as the sun ascended light cumuli formed round them,
increasing in density up to a certain point; below these clouds the air
of the valley was transparent; above them the air of heaven was still
more so; and thus they swung midway between heaven and earth, ranging
themselves in a level line along the necks of the mountains.
[Sidenote: GENERATION OF CLOUDS. 1858.]
It might be supposed that the presence of the sun heating the air would
tend to keep it more transparent, by increasing its capacity to dissolve
all visible cloud; and this indeed is the true action of the sun. But it
is not the only action. His rays, as he climbed the eastern heaven, shot
more and more deeply into the valley of St. Nicholas, the moisture of
which rose as invisible vapour, remaining unseen as long as the air
possessed sufficient warmth to keep it in the vaporous state. High up,
however, the cold crags which had lost their heat by radiation the night
before, acted like condensers upon the ascending vapour, and caused it
to curdle into visible fog. The current, however, continued ascensional,
and the clouds were slowly lifted above the tallest peaks, where they
arranged themselves in fantastic forms, shifting and changing shape as
they gradually melted away. One peak stood like a field-officer with
his cap raised above his head, others sent straggling cloud-balloons
upwards; but on watching these outliers they were gradually seen to
disappear. At first they shone like snow in the sunlight, but as they
became more attenuated they changed colour, passing through a dull red
to a dusky purple hue, until finally they left no trace of their
existence.
[Sidenote: THE ROCKS WARMED. 1858.]
[Sidenote: SCENE FROM THE GÖRNER GRAT. 1858.]
As the day advanced, warming the rocks, the clouds wholly disappeared,
and a hyaline air formed the setting of both glaciers and mountains. I
climbed to the Görner Grat to obtain a general view of the surrounding
scene. Looking towards the origin of the Görner glacier the view was
bounded by a wide col, upon which stood two lovely rounded eminences
enamelled with snow of perfect purity. They shone like burnished silver
in the sunlight, as if their surfaces had been melted and recongealed to
frosted mirrors from which the rays were flung. To the right of these
were the bounding crags of Monte Rosa, and then the body of the mountain
itself, with its crest of crag and coat of snows. To the right of Monte
Rosa, and almost rivalling it in height, was the vast mass of the
Lyskamm, a rough and craggy mountain, to whose ledges clings the snow
which cannot grasp its steeper walls, sometimes leaning over them in
impending precipices, which often break, and send wild avalanches into
the space below. Between the Lyskamm and Monte Rosa lies a large wide
valley into which both mountains pour their snows, forming there the
Western glacier of Monte Rosa[A]--a noble ice stream, which from its
magnitude and permanence deserves to impose its name upon the trunk
glacier. It extends downwards from the col which unites the two
mountains; riven and broken at some places, but at others stretching
white and pure down to its snow-line, where the true glacier emerges
from the _névé_. From the rounded shoulders of the Twin Castor a glacier
descends, at first white and shining, then suddenly broken into faults,
fissures, and precipices, which are afterwards repaired, and the glacier
joins that of Monte Rosa before the junction of the latter with the
trunk stream. Next came a boss of rock, with a secondary glacier
clinging to it as if plastered over it, and after it the Schwarze
glacier, bounded on one side by the Breithorn, and on the other by the
Twin Pollux. This glacier is of considerable magnitude. Over its upper
portion rise the Twin eminences, pure and white; then follows a smooth
and undulating space, after passing which the _névé_ is torn up into a
collection of peaks and chasms; these, however, are mended lower down,
and the glacier moves smoothly and calmly to meet its brothers in the
main valley. Next comes the Trifti glacier,[B] embraced on all sides by
the rocky arms of the Breithorn; its mass is not very great, but it
descends in a graceful sweep, and exhibits towards its extremity a
succession of beautiful bands. Afterwards we have the glacier of the
Petit Mont Cervin and those of St. Théodule, which latter are the last
that empty their frozen cargoes into the valley of the Görner. All the
glaciers here mentioned are welded together to a common trunk which
squeezes itself through the narrow defile at the base of the Riffelhorn.
Soon afterwards the moraines become confused, the glacier drops steeply
to its termination, and ploughs up the meadows in front of it with its
irresistible share.
In a line with the Riffelhorn, and rising over the latter so high as to
make it almost vanish by comparison, was the Titan obelisk of the
Matterhorn, from the base of which the Furgge glacier struggles
downwards. On the other side are the Zmutt glacier, the Schönbühl, and
the Hochwang, from the Dent Blanche; the Gabelhorn and Trift glaciers,
from the summits which bear those names. Then come the glaciers of the
Weisshorn. Describing a curve still farther to the right we alight on
the peaks of the Mischabel, dark and craggy precipices from this side,
though from the Æggischhorn they appear as cones of snow. Sweeping by
the Alphubel, the Allaleinhorn, the Rympfischorn, and Strahlhorn--all of
them majestic--we reach the pass of the Weissthor, and the Cima di
Jazzi. This completes the glorious circuit within the observer's view.
[Sidenote: COMPASS AT FAULT. 1858.]
I placed my compass upon a piece of rock to find the bearing of the
Görner glacier, and was startled at seeing the sun and it at direct
variance. What the sun declared to be north, the needle affirmed to be
south. I at first supposed that the maker had placed the S where the N
ought to be, and _vice versâ_. On shifting my position, however, the
needle shifted also, and I saw immediately that the effect was due to
the rock of the Grat. Sometimes one end of the needle _dipped_ forcibly,
at other places it whirled suddenly round, indicating an entire change
of polarity. The rock was evidently to be regarded as an assemblage of
magnets, or as a single magnet full of "consequent points." A distance
of transport not exceeding an inch was, in some cases, sufficient to
reverse the position of the needle. I held the needle between the two
sides of a long fissure a foot wide. The needle set _along_ the fissure
at some places, while at others it set _across_ it. Sometimes a little
jutting knob would attract the north end of the needle, while a closely
adjacent little knob would forcibly repel it, and attract the south end.
One extremity of a ledge three feet long was north magnetic, the other
end was south magnetic, while a neutral point existed midway between the
two, the ledge having therefore the exact polar arrangement of an
ordinary bar-magnet. At the highest point of the rock the action
appeared to be most intense, but I also found an energetic polarity in a
mass at some distance below the summit.
[Sidenote: MAGNETISM OF ROCKS. 1858.]
Remembering that Professor Forbes had noticed some peculiar magnetic
effect upon the Riffelhorn, I resolved to ascend it. Descending from the
Grat we mounted the rocks which form the base of the horn; these are
soft and soapy from the quantity of mica which they contain; the higher
rocks of the horn are, however, very dense and hard. The ascent is a
pleasant bit of mountain practice. We climbed the walls of rock, and
wound round the ledges, seeking the assailable points. I tried the
magnetic condition of the rocks as we ascended, and found it in general
feeble. In other respects the Riffelhorn is a most remarkable mass. The
ice of the Görner glacier of former ages, which rose hundreds, perhaps
thousands of feet above its present level, encountered the horn in its
descent, and was split by the latter, a diversion of the ice along the
sides of the peak being the consequence. Portions of the vertical walls
of the horn are polished by this action as if they had come from the
hands of a lapidary, and the scratchings are as sharp and definite as if
drawn by points of steel. I never saw scratchings so perfectly
preserved: the finest lines are as clear as the deepest, a consequence
of the great density and durability of the rock. The latter evidently
contains a good deal of iron, and its surface near the summit is of the
rich brown red due to the peroxide of the metal. When we fairly got
among the precipices we left our hatchets behind us, trusting
subsequently to our hands and feet alone. Squeezing, creeping, clinging,
and climbing, in due time we found ourselves upon the summit of the
horn.
[Sidenote: ASCENT OF THE RIFFELHORN. 1858.]
A pile of stones had been erected near the point where we gained the
top. I examined the stones of this pile, and found them strongly polar.
The surrounding rocks also showed a violent action, the needle
oscillating quickly, and sometimes twirling swiftly round upon a slight
change of position. The fragments of rock scattered about were also
polar. Long ledges showed north magnetism for a considerable length, and
again for an equal length south magnetism. Two parallel masses separated
from each other by a fissure, showed the same magnetic distribution.
While I was engaged at one end of the horn, Lauener wandered to the
other, on which stood two or three _hommes de pierres_. He was about
disturbing some of the stones, when a yell from me surprised him. In
fact, the thought had occurred to me that the magnetism of the horn had
been developed by lightning striking upon it, and my desire was to
examine those points which were most exposed to the discharge of the
atmospheric electricity; hence my shout to my guide to let the stones
alone. I worked towards the other end of the horn, examining the rocks
in my way. Two weathered prominences, which seemed very likely
recipients of the lightning, acted violently upon the needle. I
sometimes descended a little way, and found that among the rocks below
the summit the action was greatly enfeebled. On reaching another very
prominent point, I found its extremity all north polar, but at a little
distance was a cluster of consequent points, among which the transport
of a few inches was sufficient to turn the needle round and round.
[Sidenote: MAGNETISM OF THE HORN. 1858.]
The piles of stone at the Zermatt end of the horn did not seem so
strongly polar as the pile at the other end, which was higher; still a
strong polar action was manifested at many points of the surrounding
rocks. Having completed the examination of the summit, I descended the
horn, and examined its magnetic condition as I went along. It seemed to
me that the jutting prominences always exhibited the strongest action. I
do not indeed remember any case in which a strong action did not
exhibit itself at the ends of the terraces which constitute the horn. In
all cases, however, the rock acted as a number of magnets huddled
confusedly together, and not as if its entire mass was endowed with
magnetism of one kind.
[Illustration: Fig. 8. Magnetic Boulder of the Riffelhorn.]
On the evening of the same day I examined the lower spur of the
Riffelhorn. Amid its fissures and gullies one feels as if wandering
through the ruins of a vast castle or fortification; the precipices are
so like walls, and the scratching and polishing so like what might be
done by the hands of man. I found evidences of strong polar action in
some of the rocks low down. In the same continuous mass the action would
sometimes exhibit itself over an area of small extent, while the
remainder of the rock showed no appreciable action. Some of the boulders
cast down from the summit exhibited a strong and varied polarity. Fig. 8
is a sketch of one of these; the barbed end of each arrow represents the
north end of the needle, which assumed the various positions shown in
the figure. Midway down the spur I lighted upon a transverse wall of
rock, which formed in earlier ages the boundary of a lateral outlet of
the Görner glacier. It was red and hard, weathered rough at some places,
and polished smooth at others. The lines were drawn finely upon it, but
its outer surface appeared to be peeling off like a crust; the polished
layer rested upon the rock like a kind of enamel. The action of the
glacier appeared to resemble that of the break of a locomotive upon
rails, both being cases of exfoliation brought about by pressure and
friction. This wall measured twenty-eight yards across, and one end of
it, for a distance of ten or twelve yards, was all north polar; the
other end for a similar distance was south polar, but there was a pair
of consequent points at its centre.
[Sidenote: THE MAGNETIC FORCE. 1868.]
To meet the case of my young readers, I will here say a few words about
the magnetic force. The common magnetic needle points nearly north and
south; and if a bit of iron be brought near to either end of the needle,
they will mutually attract each other. A piece of lead will not show
this effect, nor will copper, gold, nor silver. Iron, in fact, is a
magnetic metal, which the others are not. It is to be particularly
observed, that the bit of iron attracts _both ends_ of the needle when
it is presented to them in succession; and if a common steel sewing
needle be substituted for the iron it will be seen that it also has the
power of attracting both ends of the magnetic needle. But if the needle
be rubbed once or twice along one end of a magnet, it will be found that
one of its ends will afterwards _repel_ a certain end of the magnetic
needle and attract the other. By rubbing the needle on the magnet, we
thus develop both attraction and repulsion, and this double action of
the magnetic force is called its _polarity_; thus the steel which was at
first simply _magnetic_, is now magnetic and _polar_.
It is the aim of persons making magnets, that each magnet should have
but _two_ poles, at its two ends; it is, however, easy to develop in the
same piece of steel several pairs or poles; and if the magnetization be
irregular, this is sometimes done when we wish to avoid it. These
irregular poles are called _consequent points_.
Now I want my young reader to understand that it is not only because the
rocks of the Görner Grat and Riffelhorn contain iron, that they exhibit
the action which I have described. They are not only magnetic, as common
iron is, but, like the magnetized steel needle, they are magnetic and
polar. And these poles are irregularly distributed like the "consequent
points" to which I have referred, and this is the reason why I have used
the term.
[Sidenote: BEARINGS FROM THE RIFFELHORN. 1858.]
Professor Forbes, as I have already stated, was the first to notice the
effect of the Riffelhorn upon the magnetic needle, but he seems to have
supposed that the entire mass of the mountain exercised "a local
attraction" upon the needle; (upon which end he does not say). To enable
future observers to allow for this attraction, he took the bearing of
several of the surrounding mountains from the Riffelhorn; but it is very
probable that had he changed his position a few inches, and perfectly
certain had he changed it a few yards, he would have found a set of
bearings totally different from those which he has recorded. The close
proximity and irregular distribution of its consequent points would
prevent the Riffelhorn from exerting any appreciable influence on _a
distant needle_, as in this case the local poles would effectually
neutralize each other.
FOOTNOTES:
[A] Now called, in the Federal map, the 'Grenz glacier.'--L. C. T.
[B] I take this name from Studer's map. Sometimes, however, I have
called it the "Breithorn glacier."
(21.)
[Sidenote: MONT CERVIN AS CLOUD-MAKER. 1858.]
On the morning of the 15th the Riffelberg was swathed in a dense fog,
through which heavy rain showered incessantly. Towards one o'clock the
continuity of the gray mass was broken, and sky-gleams of the deepest
blue were seen through its apertures; these would close up again, and
others open elsewhere, as if the fog were fighting for existence with
the sun behind it. The sun, however, triumphed, the mountains came more
and more into view, and finally the entire air was swept clear. I went
up to the Görner Grat in the afternoon, and examined more closely the
magnetism of its rocks; here, as on the Riffelhorn, I found it most
pronounced at the jutting prominences of the Grat. Can it be that the
superior exposure is more favourable to the formation of the magnetic
oxide of iron? I secured a number of fragments, which I still possess,
and which act forcibly upon a magnetic needle. The sun was near the
western horizon, and I remained alone upon the Grat to see his last
beams illuminate the mountains, which, with one exception, were without
a trace of cloud. This exception was the Matterhorn, the appearance of
which was extremely instructive. The obelisk appeared to be divided in
two halves by a vertical line drawn from its summit half way down, to
the windward of which we had the bare cliffs of the mountain; and to the
left of it a cloud which appeared to cling tenaciously to the rocks. In
reality, however, there was no clinging; the condensed vapour
incessantly got away, but it was ever renewed, and thus a river of cloud
had been sent from the mountain over the valley of Aosta. The wind in
fact blew lightly up the valley of St. Nicholas charged with moisture,
and when the air that held it rubbed against the cold cone of the
Matterhorn the vapour was chilled and precipitated in his lee. The
summit seemed to smoke sometimes like a burning mountain; for
immediately after its generation, the fog was drawn away in long
filaments by the wind. As the sun sank lower the ruddiness of his light
augmented, until these filaments resembled streamers of flame. The sun
sank deeper, the light was gradually withdrawn, and where it had
entirely vanished it left the mountain like a desolate old man whose
"hoary hair
Stream'd like a meteor in the troubled air."
For a moment after the sun had disappeared the scene was amazingly
grand. The distant west was ruddy, copious gray smoke-wreaths were
wafted from the mountains, while high overhead, in an atmospheric region
which seemed perfectly motionless, floated a broad thin cloud, dyed with
the richest iridescences. The colours were of the same character as
those which I had seen upon the Aletschhorn, being due to interference,
and in point of splendour and variety far exceeded anything ever
produced by the mere coloured light of the setting sun.
[Sidenote: CELLS IN THE ICE. 1858.]
On the 16th I was early upon the glacier. It had frozen hard during the
night, and the partially liberated streams flowed, in many cases, over
their own ice. I took some clear plates from under the water, and found
in them numerous liquid cells, each associated with an air-bubble or a
vacuous spot. The most common shape of the cells was a regular hexagon,
but there were all forms between the perfect hexagon and the perfect
circle. Many cells had also crimped borders, intimating that their
primitive form was that of a flower with six leaves. A plate taken from
ice which was defended from the sunbeams by the shadow of a rock had no
such cells; so that those that I observed were probably due to solar
radiation.
My first aim was to examine the structure of the Görnerhorn glacier,[A]
which descends the breast of Monte Rosa until it is abruptly cut off by
the great Western glacier of the mountain.[B] Between them is a moraine
which is at once terminal as regards the former, and lateral as regards
the latter. The ice is veined vertically along the moraine, the
direction of the structure being parallel to the latter. I ascended the
glacier, and found, as I retreated from the place where the thrust was
most violent, that the structure became more feeble. From the glacier I
passed to the rocks called "_auf der Platte_," so as to obtain a general
view of its terminal portion. The gradual perfecting of the structure as
the region of pressure was approached was very manifest: the ice at the
end seemed to wrinkle up in obedience to the pressure, the structural
furrows, from being scarcely visible, became more and more decided, and
the lamination underneath correspondingly pronounced, until it finally
attained a state of great perfection.
[Sidenote: STRUCTURE OF THE ICE. 1858.]
I now quitted the rocks and walked straight across the Western glacier
of Monte Rosa to its centre, where I found the structure scarcely
visible. I next faced the Görner Grat, and walked down the glacier
towards the moraine which divides it from the Görner glacier. The
mechanical conditions of the ice here are quite evident; each step
brought me to a place of greater pressure, and also to a place of more
highly developed structure, until finally near to the moraine itself,
and running parallel to it, a magnificent lamination was developed. Here
the superficial groovings could be traced to great distances, and beside
the moraine were boulders poised on pedestals of ice through which the
blue veins ran. At some places the ice had been weathered into laminæ
not more than a line in thickness.
I now recrossed the Monte Rosa glacier to its junction with the
Schwartze glacier, which descends between the Twins and Breithorn. The
structure of the Monte Rosa glacier is here far less pronounced than at
the other side, and the pressure which it endures is also manifestly
less; the structure of the Schwartze glacier is fairly developed, being
here parallel to its moraine. The cliffs of the Breithorn are much
exposed to weathering action, and boulders are copiously showered down
upon the adjacent ice. Between the Schwartze glacier and the glacier
which descends from the breast of the Breithorn itself these blocks ride
upon a spine of ice, and form a moraine of grand proportions. From it a
fine view of the glacier is attainable, and the gradual development of
its structure as the region of maximum pressure is approached is very
plain. A number of gracefully curved undulations sweep across the
Breithorn glacier, which are squeezed more closely together as the
moraine is approached. All the glaciers that descend from the flanking
mountains of the Görner valley are suddenly turned aside where they meet
the great trunk stream, and are reduced by the pressure to narrow
stripes of ice separated from each other by parallel moraines.
[Sidenote: TRIBUTARIES EXPLORED. 1858.]
I ascended the Breithorn glacier to the base of an ice-fall, on one side
of which I found large crumples produced by the pressure, the veined
structure being developed at right angles to the direction of the
latter. No such structure was visible above this place. The crumples
were cut by fissures, perpendicular to which the blue veins ran. I now
quitted the glacier, and clambered up the adjacent alp, from which a
fine view of the general surface was attainable. As in the case of the
Görnerhorn glacier, the gradual perfecting of the structure was very
manifest; the dirt, which first irregularly scattered over the surface,
gradually assumed a striated appearance, and became more and more
decided as the moraine was approached. Descending from the alp, I
endeavoured to measure some of the undulations; proceeding afterwards to
the junction of the Breithorn glacier with that of St. Théodule. The end
of the latter appears to be crumpled by its thrust against the former,
and the moraine between them, instead of being raised, runs along a
hollow which is flanked by the crumples on either side. The Breithorn
glacier became more and more attenuated, until finally it actually
vanished under its own moraines. On the sides of the crevasses, by which
the Théodule glacier is here intersected, I thought I could plainly see
two systems of veins cutting each other at an angle of fifteen or twenty
degrees. Reaching the Görner glacier, at a place where its dislocation
was very great, I proceeded down it past the Riffelhorn, to a point
where it seemed possible to scale the opposite mountain wall. Here I
crossed the glacier, treading with the utmost caution along the combs of
ice, and winding through the entanglement of crevasses until the spur of
the Riffelhorn was reached; this I climbed to its summit, and afterwards
crossed the green alp to our hotel.
[Sidenote: TEMPTATION. 1858.]
The foregoing good day's work was rewarded by a sound sleep at night.
The tourists were called in succession next morning, but after each call
I instantly subsided into deep slumber, and thus healthily spaced out
the interval of darkness. Day at length dawned and gradually brightened.
I looked at my watch and found it twenty minutes to six. My guide had
been lent to a party of gentlemen who had started at three o'clock for
the summit of Monte Rosa, and he had left with me a porter who undertook
to conduct me to one of the adjacent glaciers. But as I looked from my
window the unspeakable beauty of the morning filled me with a longing to
see the world from the top of Monte Rosa. I was in exceedingly good
condition--could I not reach the summit alone? Trained and indurated as
I had been, I felt that the thing was possible; at all events I could
try, without attempting anything which was not clearly within my power.
FOOTNOTES:
[A] Now called, in the Federal map, the "Monte Rosa glacier." Görnerhorn
is an old local name for the central mass of Monte Rosa.--L. C. T.
[B] _See_ p. 138, footnote.
SECOND ASCENT OF MONTE ROSA, 1858.
(22.)
[Sidenote: A LIGHT SCRIP. 1858.]
Whether my exercise be mental or bodily, I am always most vigorous when
cool. During my student life in Germany, the friends who visited me
always complained of the low temperature of my room, and here among the
Alps it was no uncommon thing for me to wander over the glaciers from
morning till evening in my shirt-sleeves. My object now was to go as
light as possible, and hence I left my coat and neckcloth behind me,
trusting to the sun and my own motion to make good the calorific waste.
After breakfast I poured what remained of my tea into a small glass
bottle, an ordinary demi-bouteille, in fact; the waiter then provided me
with a ham sandwich, and, with my scrip thus frugally furnished, I
thought the heights of Monte Rosa might be won. I had neither brandy nor
wine, but I knew the immense amount of mechanical force represented by
four ounces of bread and ham, and I therefore feared no failure from
lack of nutriment. Indeed, I am inclined to think that both guides and
travellers often impair their vigour and render themselves cowardly and
apathetic by the incessant "refreshing" which they deem it necessary to
indulge in on such occasions.
[Sidenote: THE GUIDE EXPOSTULATES. 1858.]
[Sidenote: THE GUIDE HALTS. 1858.]
The guide whom Lauener intended for me was at the door; I passed him and
desired him to follow me. This he at first refused to do, as he did not
recognise me in my shirt-sleeves; but his companions set him right, and
he ran after me. I transferred my scrip to his shoulders, and led the
way upward. Once or twice he insinuated that that was not the way to the
Schwarze-See, and was probably perplexed by my inattention. From the
summit of the ridge which bounds the Görner glacier the whole grand
panorama revealed itself, and on the higher slopes of Monte Rosa--so
high, indeed, as to put all hope of overtaking them, or even coming near
them, out of the question--a row of black dots revealed the company
which had started at three o'clock from the hotel. They had made
remarkably good use of their time, and I was afterwards informed that
the cause of this was the intense cold, which compelled them to keep up
the proper supply of heat by increased exertion. I descended swiftly to
the glacier, and made for the base of Monte Rosa, my guide following at
some distance behind me. One of the streams, produced by superficial
melting, had cut for itself a deep wide channel in the ice; it was not
too wide for a spring, and with the aid of a run I cleared it and went
on. Some minutes afterwards I could hear the voice of my companion
exclaiming, in a tone of expostulation, "No, no, I won't follow you
there." He however made a circuit, and crossed the stream; I waited for
him at the place where the Monte Rosa glacier joins the rock, "_auf der
Platte_," and helped him down the ice-slope. At the summit of these
rocks I again waited for him. He approached me with some excitement of
manner, and said that it now appeared plain to him that I intended to
ascend Monte Rosa, but that he would not go with me. I asked him to
accompany me to the summit of the next cliff, which he agreed to do; and
I found him of some service to me. He discovered the faint traces of the
party in advance, and, from his greater experience, could keep them
better in view than I could. We lost them, however, near the base of the
cliff at which we aimed, and I went on, choosing as nearly as I could
remember the route followed by Lauener and myself a week previously,
while my guide took another route, seeking for the traces. The glacier
here is crevassed, and I was among the fissures some distance in advance
of my companion. Fear was manifestly getting the better of him, and he
finally stood still, exclaiming, "No man can pass there." At the same
moment I discovered the trace, and drew his attention to it; he
approached me submissively, said that I was quite right, and declared
his willingness to go on. We climbed the cliff, and discovered the trace
in the snow above it. Here I transferred the scrip and telescope to my
own shoulders, and gave my companion a cheque for five francs. He
returned, and I went on alone.
The sun and heaven were glorious, but the cold was nevertheless intense,
for it had frozen bitterly the night before. The mountain seemed more
noble and lovely than when I had last ascended it; and as I climbed the
slopes, crossed the shining cols, and rounded the vast snow-bosses of
the mountain, the sense of being alone lent a new interest to the
glorious scene. I followed the track of those who preceded me, which was
that pursued by Lauener and myself a week previously. Once I deviated
from it to obtain a glimpse of Italy over the saddle which stretches
from Monte Rosa to the Lyskamm. Deep below me was the valley, with its
huge and dislocated _névé_, and the slope on which I hung was just
sufficiently steep to keep the attention aroused without creating
anxiety. I prefer such a slope to one on which the thought of danger
cannot be entertained. I become more weary upon a dead level, or in
walking up such a valley as that which stretches between Visp and
Zermatt, than on a steep mountain side. The sense of weariness is often
no index to the expenditure of muscular force: the muscles may be
charged with force, and, if the nervous excitant be feeble, the strength
lies dormant, and we are tired without exertion. But the thought of
peril keeps the mind awake, and spurs the muscles into action; they move
with alacrity and freedom, and the time passes swiftly and pleasantly.
[Sidenote: LEFT ALONE. 1858.]
Occupied with my own thoughts as I ascended, I sometimes unconsciously
went too quickly, and felt the effects of the exertion. I then slackened
my pace, allowing each limb an instant of repose as I drew it out of the
snow, and found that in this way walking became rest. This is an
illustration of the principle which runs throughout nature--to
accomplish physical changes, _time_ is necessary. Different positions of
the limb require different molecular arrangements; and to pass from one
to the other requires time. By lifting the leg slowly and allowing it to
fall forward by its own gravity, a man may get on steadily for several
hours, while a very slight addition to this pace may speedily exhaust
him. Of course the normal pace differs in different persons, but in all
the power of endurance may be vastly augmented by the prudent outlay of
muscular force.
The sun had long shone down upon me with intense fervour, but I now
noticed a strange modification of the light upon the slopes of
snow. I looked upwards, and saw a most gorgeous exhibition of
interference-colours. A light veil of clouds had drawn itself between me
and the sun, and this was flooded with the most brilliant dyes. Orange,
red, green, blue--all the hues produced by diffraction were exhibited in
the utmost splendour. There seemed a tendency to form circular zones of
colour round the sun, but the clouds were not sufficiently uniform to
permit of this, and they were consequently broken into spaces, each
steeped with the colour due to the condition of the cloud at the place.
Three times during my ascent similar veils drew themselves across the
sun, and at each passage the splendid phenomena were renewed. As I
reached the middle of the mountain an avalanche was let loose from the
sides of the Lyskamm; the thunder drew my eyes to the place; I saw the
ice move, but it was only the tail of the avalanche; still the volume of
sound told me that it was a huge one. Suddenly the front of it appeared
from behind a projecting rock, hurling its ice-masses with fury into the
valley, and tossing its rounded clouds of ice-dust high into the
atmosphere. A wild long-drawn sound, multiplied by echoes, now descended
from the heights above me. It struck me at first as a note of
lamentation, and I thought that possibly one of the party which was now
near the summit had gone over the precipice. On listening more
attentively I found that the sound shaped itself into an English
"hurrah!" I was evidently nearing the party, and on looking upwards I
could see them, but still at an immense height above me. The summit
still rose before them, and I therefore thought the cheer premature. A
precipice of ice was now in front of me, around which I wound to the
right, and in a few minutes found myself fairly at the bottom of the
Kamm.
[Sidenote: GIDDINESS ON THE KAMM. 1858.]
[Sidenote: SCRIP LEFT BEHIND. 1858.]
I paused here for a moment, and reflected on the work before me. My head
was clear, my muscles in perfect condition, and I felt just sufficient
fear to render me careful. I faced the Kamm, and went up slowly but
surely, and soon heard the cheer which announced the arrival of the
party at the summit of the mountain. It was a wild, weird, intermittent
sound, swelling or falling as the echoes reinforced or enfeebled it. In
getting through the rocks which protrude from the snow at the base of
the last spur of the mountain, I once had occasion to stoop my head,
and, on suddenly raising it, my eyes swam as they rested on the unbroken
slope of snow at my left. The sensation was akin to giddiness, but I
believe it was chiefly due to the absence of any object upon the snow
upon which I could converge the axes of my eyes. Up to this point I had
eaten nothing. I now unloosed my scrip, and had two mouthfuls of
sandwich and nearly the whole of the tea that remained. I found here
that my load, light as it was, impeded me. When fine balancing is
necessary, the presence of a very light load, to which one is
unaccustomed, may introduce an element of danger, and for this reason I
here left the residue of my tea and sandwich behind me. A long, long
edge was now in front of me, sloping steeply upwards. As I commenced the
ascent of this, the foremost of those whose cheer had reached me from
the summit some time previously, appeared upon the top of the edge, and
the whole party was seen immediately afterwards dangling on the Kamm. We
mutually approached each other. Peter Bohren, a well-known Oberland
guide, came first, and after him came the gentleman in his immediate
charge. Then came other guides with other gentlemen, and last of all my
guide, Lauener, with his strong right arm round the youngest of the
party. We met where a rock protruded through the snow. The cold smote my
naked throat bitterly, so to protect it I borrowed a handkerchief from
Lauener, bade my new acquaintances good bye, and proceeded upwards. I
was soon at the place where the snow-ridge joins the rocks which
constitute the crest of the mountain; through these my way lay, every
step I took augmenting my distance from all life, and increasing my
sense of solitude. I went up and down the cliffs as before, round
ledges, through fissures, along edges of rock, over the last deep and
rugged indentation, and up the rocks at its opposite side, to the
summit.
[Sidenote: ALONE ON THE SUMMIT. 1858.]
[Sidenote: THE AXE SLIPS. 1858.]
A world of clouds and mountains lay beneath me. Switzerland, with its
pomp of summits, was clear and grand; Italy was also grand, but more
than half obscured. Dark cumulus and dark crag vied in savagery, while
at other places white snows and white clouds held equal rivalry. The
scooped valleys of Monte Rosa itself were magnificent, all gleaming in
the bright sunlight--tossed and torn at intervals, and sending from
their rents and walls the magical blue of the ice. Ponderous _névés_ lay
upon the mountains, apparently motionless, but suggesting
motion--sluggish, but indicating irresistible dynamic energy, which
moved them slowly to their doom in the warmer valleys below. I thought
of my position: it was the first time that a man had stood alone upon
that wild peak, and were the imagination let loose amid the surrounding
agencies, and permitted to dwell upon the perils which separated the
climber from his kind, I dare say curious feelings might have been
engendered. But I was prompt to quell all thoughts which might lessen my
strength, or interfere with the calm application of it. Once indeed an
accident made me shudder. While taking the cork from a bottle which is
deposited on the top, and which contains the names of those who have
ascended the mountain, my axe slipped out of my hand, and slid some
thirty feet away from me. The thought of losing it made my flesh creep,
for without it descent would be utterly impossible. I regained it, and
looked upon it with an affection which might be bestowed upon a living
thing, for it was literally my staff of life under the circumstances.
One look more over the cloud-capped mountains of Italy, and I then
turned my back upon them, and commenced the descent.
The brown crags seemed to look at me with a kind of friendly
recognition, and, with a surer and firmer feeling than I possessed on
ascending, I swung myself from crag to crag and from ledge to ledge with
a velocity which surprised myself. I reached the summit of the Kamm, and
saw the party which I had passed an hour and a half before, emerging
from one of the hollows of the mountain; they had escaped from the edge
which now lay between them and me. The thought of the possible loss of
my axe at the summit was here forcibly revived, for without it I dared
not take a single step. My first care was to anchor it firmly in the
snow, so as to enable it to bear at times nearly the whole weight of my
body. In some places, however, the anchor had but a loose hold; the
"cornice" to which I have already referred became granular, and the
handle of the axe went through it up to the head, still, however,
remaining loose. Some amount of trust had thus to be withdrawn from the
staff and placed in the limbs. A curious mixture of carelessness and
anxiety sometimes fills the mind on such occasions. I often caught
myself humming a verse of a frivolous song, but this was mechanical, and
the substratum of a man's feelings under such circumstances is real
earnestness. The precipice to my left was a continual preacher of
caution, and the slope to my right was hardly less impressive. I looked
down the former but rarely, and sometimes descended for a considerable
time without looking beyond my own footsteps. The power of a thought was
illustrated on one of these occasions. I had descended with extreme
slowness and caution for some time, when looking over the edge of the
cornice I saw a row of pointed rocks at some distance below me. These I
felt must receive me if I slipped over, and I thought how before
reaching them I might so break my fall as to arrive at them unkilled.
This thought enabled me to double my speed, and as long as the spiky
barrier ran parallel to my track I held my staff in one hand, and
contented myself with a slight pressure upon it.
I came at length to a place where the edge was solid ice, which rose to
the level of the cornice, the latter appearing as if merely stuck
against it. A groove ran between the ice and snow, and along this groove
I marched until the cornice became unsafe, and I had to betake myself to
the ice. The place was really perilous, but, encouraging myself by the
reflection that it would not last long, I carefully and deliberately
hewed steps, causing them to dip a little inward, so as to afford a
purchase for the heel of my boot, never forsaking one till the next was
ready, and never wielding my hatchet until my balance was secured. I was
soon at the bottom of the Kamm, fairly out of danger, and full of glad
vigour I bore swiftly down upon the party in advance of me. It was an
easy task to me to fuse myself amongst them as if I had been an old
acquaintance, and we joyfully slid, galloped, and rolled together down
the residue of the mountain.
[Sidenote: ACCIDENT ON THE KAMM. 1858.]
The only exception was the young gentleman in Lauener's care. A day or
two previously he had, I believe, injured himself in crossing the Gemmi,
and long before he reached the summit of Monte Rosa his knee swelled,
and he walked with great difficulty. But he persisted in ascending, and
Lauener, seeing his great courage, thought it a pity to leave him
behind. I have stated that a portion of the Kamm was solid ice. On
descending this, Mr. F.'s footing gave way, and he slipped forward.
Lauener was forced to accompany him, for the place was too steep and
slippery to permit of their motion being checked. Both were on the point
of going over the Lyskamm side of the mountain, where they would have
indubitably been dashed to pieces. "There was no escape there," said
Lauener, in describing the incident to me subsequently, "but I saw a
possible rescue at the other side, so I sprang to the right, forcibly
swinging my companion round; but in doing so, the bâton tripped me up;
we both fell, and rolled rapidly over each other down the incline. I
knew that some precipices were in advance of us, over which we should
have gone, so, releasing myself from my companion, I threw myself in
front of him, stopped myself with my axe, and thus placed a barrier
before him." After some vain efforts at sliding down the slopes on a
bâton, in which practice I was fairly beaten by some of my new friends,
I attached myself to the invalid, and walked with him and Lauener
homewards. Had I gone forward with the foremost of the party, I should
have completed the expedition to the summit and back in a little better
than nine hours.
[Sidenote: DANGER OF CLIMBING ALONE. 1858.]
I think it right to say one earnest word in connexion with this ascent;
and the more so as I believe a notion is growing prevalent that half
what is said and written about the dangers of the Alps is mere humbug.
No doubt exaggeration is not rare, but I would emphatically warn my
readers against acting upon the supposition that it is general. The
dangers of Mont Blanc, Monte Rosa, and other mountains, are real, and,
if not properly provided against, may be terrible. I have been much
accustomed to be alone upon the glaciers, but sometimes, even when a
guide was in front of me, I have felt an extreme longing to have a
second one behind me. Less than two good ones I think an arduous climber
ought not to have; and if climbing without guides were to become
habitual, deplorable consequences would assuredly sooner or later ensue.
(23.)
The 18th of August I spent upon the Furgge glacier at the base of Mont
Cervin, and what it taught me shall be stated in another place. The
evening of this day was signalised by the pleasant acquaintances which
it gave me. It was my intention to cross the Weissthor on the morning of
the 19th, but thunder, lightning, and heavy rain opposed the project,
and with two friends I descended, amid pitiless rain, to Zermatt. Next
day I walked by way of Stalden to Saas, where I made the acquaintance of
Herr Imseng, the Curé, and on the 21st ascended to the Distel Alp. Near
to this place the Allalein glacier pushes its huge terminus right across
the valley and dams up the streams descending from the mountains higher
up, thus giving birth to a dismal lake. At one end of this stands the
Mattmark hotel, which was to be my headquarters for a few days.
[Sidenote: ASCENT OF A BOULDER. 1858.]
I reached the place in good company. Near to the hotel are two
magnificent boulders of green serpentine, which have been lodged there
by one of the lateral glaciers; and two of the ladies desiring to ascend
one of these rocks, a friend and myself helped them to the top. The
thing was accomplished in a very spirited way. Indeed the general
contrast, in regard to energy, between the maidens of the British Isles
and those of the Continent and of America is extraordinary. Surely those
who talk of this country being in its old age overlook the physical
vigour of its sons and daughters. They are strong, but from a
combination of the greatest forces we may obtain a small resultant,
because the forces may act in opposite directions and partly neutralize
each other. Herein, in fact, lies Britain's weakness; it is strength
ill-directed; and is indicative rather of the perversity of young blood
than of the precision of mature years.
[Sidenote: DISMAL QUARTERS. 1858.]
Immediately after this achievement I was forsaken by my friends, and
remained the only visitor in the hotel. A dense gray cloud gradually
filled the entire atmosphere, from which the rain at length began to
gush in torrents. The scene from the windows of the hotel was of the
most dismal character; the rain also came through the roof, and dripped
from the ceiling to the floor. I endeavoured to make a fire, but the air
would not let the smoke of the pine-logs ascend, and the biting of the
hydrocarbons was excruciating to the eyes. On the whole, the cold was
preferable to the smoke. During the night the rain changed to snow, and
on the morning of the 22nd all the mountains were thickly covered. The
gray delta through which a river of many arms ran into the Mattmark See
was hidden; against some of the windows of the _salle à manger_ the snow
was also piled, obscuring more than half their light. I had sent my
guide to Visp, and two women and myself were the only occupants of the
place. It was extremely desolate--I felt, moreover, the chill of Monte
Rosa in my throat, and the conditions were not favourable to the cure of
a cold.
On the 23rd the Allalein glacier was unfit for work; I therefore
ascended to the summit of the Monte Moro, and found the Valaisian side
of the pass in clear sunshine, while impenetrable fog met us on the
Italian side. I examined the colour of the freshly fallen snow; it was
not an ordinary blue, and was even more transparent than the blue of the
firmament. When the snow was broken the light flashed forth; when the
staff was dug into the snow and withdrawn, the blue gleam appeared; when
the staff lay in a hole, although there might be a sufficient space all
round it, the coloured light refused to show itself.
My cough kept me awake on the night of the 23rd, and my cold was worse
next day. I went upon the Allalein glacier, but found myself by no means
so sure a climber as usual. The best guides find that their powers vary;
they are not equally competent on all days. I have heard a celebrated
Chamouni guide assert that a man's _morale_ is different on different
days. The morale in my case had a physical basis, and it probably has so
in all. The Allalein glacier, as I have said, crosses the valley and
abuts against the opposite mountain; here it is forced to turn aside,
and in consequence of the thrust and bending it is crumpled and
crevassed. The wall of the Mattmark See is a fine glacier section:
looked at from a distance, the ridges and fissures appear arranged like
a fan. The structure of the crumpled ice varies from the vertical to the
horizontal, and the ridges are sometimes split _along_ the planes of
structure. The aspect of this portion of the glacier from some of the
adjacent heights is exceedingly interesting.
[Sidenote: THE VAULT OF THE ALLALEIN. 1858.]
On the morning of the 25th I had two hours' clambering over the
mountains before breakfast, and traced the action of ancient glaciers to
a great height. The valley of Saas in this respect rivals that of Hasli;
the flutings and polishings being on the grandest scale. After breakfast
I went to the end of the Allalein glacier, where the Saas Visp river
rushes from it: the vault was exceedingly fine, being composed of
concentric arches of clear blue ice. I spent several hours here
examining the intimate structure of the ice, and found the vacuum disks
which I shall describe at another place, of the greatest service to me.
As at Rosenlaui and elsewhere, they here taught me that the glacier was
composed of an aggregate of small fragments, each of which had a
definite plane of crystallization. Where the ice was partially weathered
the surfaces of division between the fragments could be traced through
the coherent mass, but on crossing these surfaces the direction of the
vacuum disks changed, indicating a similar change of the planes of
crystallization. The blue veins of the glacier went through its
component fragments irrespective of these planes. Sometimes the vacuum
disks were parallel to the veins, sometimes across them, sometimes
oblique to them.
Several fine masses of ice had fallen from the arch upon its floor, and
these were disintegrated to the core. A kick, or a stroke of an axe,
sufficed to shake masses almost a cubic yard in size into fragments
varying not much on either side of a cubic inch. The veining was finely
preserved on the concentric arches of the vault, and some of them
apparently exhibited its abolition, or at least confusion, and fresh
development by new conditions of pressure. The river being deep and
turbulent this day, to reach its opposite side I had to climb the
glacier and cross over the crown of its highest arch; this enabled me
to get quite in front of the vault, to enter it, and closely inspect
those portions where the structure appeared to change. I afterwards
ascended the steep moraine which lies between the Allalein and the
smaller glacier to the left of it; passing to the latter at intervals to
examine its structure. I was at length stopped by the dislocated ice;
and from the heights I could count a system of seven dirt-bands, formed
by the undulations on the surface of the glacier. On my return to the
hotel I found there a number of well-known Alpine men who intended to
cross the Adler pass on the following day. Herr Imseng was there: he
came to me full of enthusiasm, and asked me whether I would join him in
an ascent of the Dom: we might immediately attack it; and he felt sure
that we should succeed. The Dom is the highest of the Mischabel peaks,
and is one of the grandest of the Alps. I agreed to join the Curé, and
with this understanding we parted for the night.
[Sidenote: AVALANCHE AT SAAS. 1858.]
Thursday, 26th August.--A wild stormy morning after a wild and rainy
night: the Adler pass being impassable, the mountaineers returned, and
Imseng informed me that the Dom must be abandoned. He gave me the
statistics of an avalanche which had fallen in the valley some years
before. Within the memory of man Saas had never been touched by an
avalanche, but a tradition existed that such a catastrophe had once
occurred. On the 14th of March, 1848, at eight o'clock in the morning,
the Curé was in his room; when he heard the cracking of pine-branches,
and inferred from the sound that an avalanche was descending upon the
village. It dashed in the windows of his house and filled his rooms with
snow; the sound it produced being sufficient to mask the crashing of the
timbers of an adjacent house. Three persons were killed. On the 3rd of
April, 1849, heavy snow fell at Saas; the Curé waited until it had
attained a depth of four feet, and then retreated to Fée. That night an
avalanche descended, and in the line of its rush was a house in which
five or six and twenty people had collected for safety: nineteen of them
were killed. The Curé afterwards showed me the site of the house, and
the direction of the avalanche. It passed through a pine wood; and on
expressing my surprise that the trees did not arrest it, he replied that
the snow was "quite like dust," and rushed among the trees like so much
water. To return from Fée to Saas on the day following he found it
necessary to carry two planks. Kneeling upon one of them, he pushed the
other forward, and transferred his weight to it, drawing the other after
him and repeating the same act. The snow was like flour, and would not
otherwise bear his weight. Seeing no prospect of fine weather, I
descended to Saas on the afternoon of the 26th. I was the only guest at
the hotel; but during the evening I was gratified by the unexpected
arrival of my friend Hirst, who was on his way over the Monte Moro to
Italy.
[Sidenote: THE FÉE GLACIER. 1858.]
[Sidenote: SNOW, VAPOUR AND CLOUD. 1858.]
For the last five days it had been a struggle between the north wind and
the south, each edging the other by turns out of its atmospheric bed,
and producing copious precipitation; but now the conflict was
decided--the north had prevailed, and an almost unclouded heaven
overspread the Alps. The few white fleecy masses that remained were good
indications of the swift march of the wind in the upper air. My friend
and I resolved to have at least one day's excursion together, and we
chose for it the glacier of the Fée. Ascending the mountain by a
well-beaten path, we passed a number of "Calvaries" filled with tattered
saints and Virgins, and soon came upon the rim of a flattened bowl quite
clasped by the mountains. In its centre was the little hamlet of Fée,
round which were fresh green pastures, and beyond it the perpetual ice
and snow. It was exceedingly picturesque--a scene of human beauty and
industry where savagery alone was to be expected. The basin had been
scooped by glaciers, and as we paused at its entrance the rounded and
fluted rocks were beneath our feet. The Alphubel and the Mischabel
raised their crowns to heaven in front of us; the newly fallen snow
clung where it could to the precipitous crags of the Mischabel, but on
the summits it was the sport of the wind. Sometimes it was borne
straight upwards in long vertical striæ; sometimes the fibrous columns
swayed to the right, sometimes to the left; sometimes the motion on one
of the summits would quite subside; anon the white peak would appear
suddenly to shake itself to dust, which it yielded freely to the wind. I
could see the wafted snow gradually melt away, and again curdle up into
true white cloud by precipitation; this in its turn would be pulled
asunder like carded wool, and reduced a second time to transparent
vapour.
In the middle of the ice of the Fée stands a green alp, not unlike the
Jardin; up this we climbed, halting at intervals upon its grassy knolls
to inspect the glacier. I aimed at those places where on à priori
grounds I should have thought the production of the veined structure
most likely, and reached at length the base of a wall of rock from the
edge of which long spears of ice depended. Here my friend halted, while
Lauener and myself climbed the precipice, and ascended to the summit of
the alp. The snow was deep at many places, and our immersions in unseen
holes very frequent. From the peak of the Fée Alp a most glorious view
is obtained; in point of grandeur it will bear comparison with any in
the Alps, and its seclusion gives it an inexpressible charm. We remained
for half an hour upon the warm rock, and then descended. It was our
habit to jump from the higher ledges into the deep snow below them, in
which we wallowed as if it were flour; but on one of these occasions I
lighted on a stone, and the shock produced a curious effect upon my
hearing. I appeared suddenly to lose the power of appreciating deep
sounds, while the shriller ones were comparatively unimpaired. After I
rejoined my friend it required attention on my part to hear him when he
spoke to me. This continued until I approached the end of the glacier,
when suddenly the babblement of streams, and a world of sounds to which
I had been before quite deaf burst in upon me. The deafness was probably
due to a strain of the tympanum, such as we can produce artificially,
and thus quench low sounds, while shrill ones are scarcely affected.
[Sidenote: "A TERRIBLE HOLE." 1858.]
I was anxious to quit Saas early next morning, but the Curé expressed so
strong a wish to show us what he called a _schauderhaftes Loch_--a
terrible hole--which he had himself discovered, that I consented to
accompany him. We were joined by his assistant and the priest of Fée.
The stream from the Fée glacier has cut a deep channel through the
rocks, and along the right-hand bank of the stream we ascended. It was
very rough with fallen crags and fallen pines amid which we once or
twice lost our way. At length we came to an aperture just sufficient to
let a man's body through, and were informed by our conductor that our
route lay along the little tunnel: he lay down upon his stomach and
squeezed himself through it like a marmot. I followed him; a second
tunnel, in which, however, we could stand upright, led into a spacious
cavern, formed by the falling together of immense slabs of rock which
abutted against each other so as to form a roof. It was the very type of
a robber den; and when I remarked this, it was at once proposed to sing
a verse from Schiller's play. The young priest had a powerful voice--he
led and we all chimed in.
[Sidenote: SONG OF THE ROBBERS. 1858.]
"Ein frohes Leben führen wir,
Ein Leben voller Wonne.
Der Wald ist unser Nachtquartier,
Bei Sturm und Wind hanthieren wir,
Der Mond ist unsre Sonne."
Herr Imseng wore his black coat; the others had taken theirs off, but
they wore their clerical hats, black breeches and stockings. We formed a
singular group in a singular place, and the echoed voices mingled
strangely with the gusts of the wind and the rush of the river.
Soon afterwards I parted from my friend, and descended the valley to
Visp, where I also parted with my guide. He had been with me from the
22nd of July to the 29th of August, and did his duty entirely to my
satisfaction. He is an excellent iceman, and is well acquainted both
with the glaciers of the Oberland and of the Valais. He is strong and
good-humoured, and were I to make another expedition of the kind I don't
think that I should take any guide in the Oberland in preference to
Christian Lauener.
(24.)
[Sidenote: CLIMBERS AND SCIENCE. 1858.]
It is a singular fact that as yet we know absolutely nothing of the
winter temperature of any one of the high Alpine summits. No doubt it is
a sufficient justification of our Alpine men, as regards their climbing,
_that they like it_. This plain reason is enough; and no man who ever
ascended that "bad eminence" Primrose Hill, or climbed to Hampstead
Heath for the sake of a freer horizon, can consistently ask a better. As
regards physical science, however, the contributions of our mountaineers
have as yet been _nil_, and hence, when we hear of the scientific value
of their doings, it is simply amusing to the climbers themselves. I do
not fear that I shall offend them in the least by my frankness in
stating this. Their pleasure is that of overcoming acknowledged
difficulties, and of witnessing natural grandeur. But I would venture to
urge that our Alpine men will not find their pleasure lessened by
embracing a scientific object in their doings. They have the strength,
the intelligence, and let them add to these the accuracy which physical
science now demands, and they may contribute work of enduring value. Mr.
Casella will gladly teach them the use of his minimum-thermometers; and
I trust that the next seven years will not pass without making us
acquainted with the winter temperature of every mountain of note in
Switzerland.[A]
I had thought of this subject since I first read the conjectures of De
Saussure on the temperature of Mont Blanc; but in 1857 I met Auguste
Balmat at the Jardin, and there learned from him that he entertained the
idea of placing a self-registering thermometer at the summit of the
mountain. Balmat was personally a stranger to me at the time, but
Professor Forbes's writings had inspired me with a respect for him,
which this unprompted idea of his augmented. He had procured a
thermometer, the graduation of which, however, he feared was not low
enough. As an encouragement to Balmat, and with the view of making his
laudable intentions known, I communicated them to the Royal Society, and
obtained from the Council a small grant of money to purchase
thermometers and to assist in the expenses of an ascent. I had now the
thermometers in my possession; and having completed my work at Zermatt
and Saas, my next desire was to reach Chamouni and place the instruments
on the top of Mont Blanc. I accordingly descended the valley of the
Rhone to Martigny, crossed the Tête Noire, and arrived at Chamouni on
the 29th of August, 1858.
[Sidenote: DIFFICULTIES AT CHAMOUNI. 1858.]
Balmat was engaged at this time as the guide of Mr. Alfred Wills, who,
however, kindly offered to place him at my disposal; and also expressed
a desire to accompany me himself and assist me in my observations. I
gladly accepted a proposal which gave me for companion so determined a
climber and so estimable a man. But Chamouni was rife with difficulties.
In 1857 the Guide Chef had the good sense to give me considerable
liberty of action. Now his mood was entirely changed: he had been
"molested" for giving me so much freedom. I wished to have a boy to
carry a small instrument for me up the Mer de Glace--he would not allow
it; I must take a guide. If I ascended Mont Blanc he declared that I
must take four guides; that, in short, I must in all respects conform to
the rules made for ordinary tourists. I endeavoured to explain to him
the advantages which Chamouni had derived from the labours of men of
science; it was such men who had discovered it when it was unknown, and
it was by their writings that the attention of the general public had
been called towards it. It was a bad recompense, I urged, to treat a man
of science as he was treating me. This was urged in vain; he shrugged
his shoulders, was very sorry, but the thing could not be changed. I
then requested to know his superior, that I might apply to him; he
informed me that there were a President and Commission of guides at
Chamouni, who were the proper persons to decide the question, and he
proposed to call them together on the 31st of August, at seven P.M., on
condition that I was to be present to state my own case. To this I
agreed.
I spent that day quite alone upon the Mer de Glace, and climbed amid a
heavy snow-storm to the Cleft station over Trélaporte. When I reached
the Montanvert I was wet and weary, and would have spent the night there
were it not for my engagement with the Guide Chef. I descended amid the
rain, and at the appointed hour went to his bureau. He met me with a
polite sympathetic shrug; explained to me that he had spoken to the
Commission, but that it could not assemble _pour une chose comma ça_;
that the rules were fixed, and I must abide by them. "Well," I
responded, "you think you have done your duty; it is now my turn to
perform mine. If no other means are available I will have this
transaction communicated to the Sardinian Government, and I don't think
that it will ratify what you have done." The Guide Chef evidently did
not believe a word of it.
Previous to taking any further step I thought it right to see the
President of the Commission of Guides, who was also Syndic of the
commune. I called upon him on the morning of the 1st of September, and,
assuming that he knew all about the transaction, spoke to him
accordingly. He listened to me for a time, but did not seem to
understand me, which I ascribed partly to my defective French
pronunciation. I expressed a hope that he did comprehend me; he said
he understood my words very well, but did not know their purport. In
fact he had not heard a single word about me or my request. He stated
with some indignation that, so far from its being a subject on which the
Commission could not assemble, it was one which it was their especial
duty to take into consideration. Our conference ended with the
arrangement that I was to write him an official letter stating the case,
which he was to forward to the Intendant of the province of Faucigny
resident at Bonneville. All this was done.
[Sidenote: THE INTENDANT MEMORIALISED. 1858.]
I subsequently memorialised the Intendant himself; and Balmat visited
him to secure his permission to accompany me. I have to record, that
from first to last the Intendant gave me his sympathy and support. He
could not alter laws, but he deprecated a "judaical" interpretation of
them. His final letter to myself was as follows:--
[Sidenote: THE INTENDANT'S RESPONSE. 1858.]
"Intendance Royale de la Province de Faucigny,
"Bonneville, 11 Septembre, 1858.
"Monsieur,--
"J'apprends avec une véritable peine les difficultés que vous
rencontrez de la part de M. le Guide Chef pour l'effectuation
de votre périlleuse entreprise scientifique, mais je dois vous
dire aussi avec regret que ces difficultés résident dans un
règlement fait en vue de la sécurité des voyageurs, quel que
puisse être le but de leurs excursions.
"Désireux néanmoins de vous être utile, notamment en la
circonstance, j'invite aujourd'hui même M. le Guide Chef à
avoir égard à votre projet, à faire en sa faveur une exception
au règlement ci-devant eu, tant qu'il n'y aura aucun danger
pour votre sûreté et celle des personnes qui vous
accompagneront, et enfin de se prêter dans les limites de ses
moyens et attributions pour l'heureux succès de l'expédition,
dont les conséquences et résultats n'intéressent pas seulement
la science, mais encore la vallée de Chamounix en particulier.
"Agréez, Monsieur,
"l'assurance de ma consideration très-distinguée.
"Pour l'Intendant en congé,
"Le Secrétaire,
"DELÉGLISE."
While waiting for this permission I employed myself in various ways. On
the 2nd of September I ascended the Brévent, from which Mont Blanc is
seen to great advantage. From Chamouni its vast slopes are so
foreshortened that one gets a very imperfect idea of the extent to be
traversed to reach the summit. What, however, struck me most on the
Brévent was the changed relation of the Aiguille du Dru and the Aiguille
Verte. From Montanvert the former appears a most imposing mass, while
the peak of the latter appears rather dwarfed behind it; but from the
Brévent the Aiguille du Dru is a mere pinnacle stuck in the breast of
the grander pyramid of the Aiguille Verte.
[Sidenote: THE "SÉRACS" REVISITED. 1858.]
On the 4th I rose early, and, strapping on my telescope, ascended to the
Montanvert, where I engaged a youth to accompany me up the glacier. The
heavens were clear and beautiful:--blue over the Aiguille du Dru, blue
over the Jorasse and Mont Mallet, deep blue over the pinnacles of
Charmoz, and the same splendid tint stretched grandly over the Col du
Géant and its Aiguille. No trace of condensation appeared till towards
eleven o'clock, when a little black balloon of cloud swung itself over
the Aiguilles Rouges. At one o'clock there were two large masses and a
little one between them; while higher up a white veil, almost too thin
to be visible, spread over a part of the heavens. At the zenith,
however, and south, north, and west, the blue seemed to deepen as the
day advanced. I visited the ice-wall at the Tacul, which seemed lower
than it was last year; the cascade of le Géant appeared also far less
imposing. Only in the early part of summer do we see the ice in its true
grandeur: its edges and surfaces are then sharp and clear, but
afterwards its nobler masses shrink under the influence of sun and air.
The _séracs_ now appeared wasted and dirty, and not the sharp angular
ice-castles which rose so grandly when I first saw them. Thirteen men
had crossed the Col du Géant on the day previous, and left an ample
trace behind them. This I followed nearly to the summit of the fall. The
condition of the glacier was totally different from that of the opposite
side on the previous year. The ice was riven, burrowed, and honeycombed,
but the track amid all was easy: a vigorous English maiden might have
ascended the fall without much difficulty. My object now was to examine
the structure of the fall; but the ice was not in a good condition for
such an examination: it was too much broken. Still a definite structure
was in many places to be traced, and some of them apparently showed
structure and bedding at a high angle to each other, but I could not be
certain of it. I paused at every commanding point of view and examined
the ice through my opera-glass; but the result was inconclusive. I
observed that the terraces which compose the fall do not front the
middle of the glacier, but turn their foreheads rather towards its
eastern side, and the consequence is that the protuberances lower down,
which are the remains of these terraces, are highest at the same side.
Standing at the base of the Aiguille Noire, and looking downwards where
the Glacier des Périades pushes itself against the Géant, a series of
fine crumples is formed on the former, cut across by crevasses, on the
walls of which a forward and backward dipping of the blue veins is
exhibited. Huge crumples are also formed by the Glacier du Géant, which
are well seen from a point nearly opposite the lowest lateral moraine of
the Glacier des Périades. In some cases the upper portions of the
crumples had scaled off so as to form arches of ice--a consequence
doubtless of the pressure.
[Sidenote: THERMOMETER AT THE JARDIN. 1858.]
The beauty of some Alpine skies is treacherous; in fact the deepest blue
often indicates an atmosphere charged almost to saturation with aqueous
vapour. This was the case on the present occasion. Soon after reaching
Chamouni in the evening, rain commenced and continued with scarcely any
intermission until the afternoon of the 8th. I had given up all hopes of
being able to ascend Mont Blanc; and hence resolved to place the
thermometers in some more accessible position. On the 9th accordingly,
accompanied by Mr. Wills, Balmat, and some other friends, I ascended to
the summit of the Jardin, where we placed two thermometers: one in the
ice, at a depth of three feet below the surface; another on a ledge of
the highest rock.[B] The boiling point of water at this place was
194.6° Fahr.
Deep snow was upon the Talèfre, and the surrounding precipices were also
heavily laden. Avalanches thundered incessantly from the Aiguille Verte
and the other mountains. Scarcely five minutes on an average intervened
between every two successive peals; and after the direct shock of each
avalanche had died away the air of the basin continued to be shaken by
the echoes reflected from its bounding walls.
[Sidenote: EVENING RED. 1858.]
The day was far spent before we had completed our work. All through the
weather had been fine, and towards evening augmented to magnificence. As
we descended the glacier from the Couvercle the sun was just
disappearing, and the western heaven glowed with crimson, which crept
gradually up the sky until finally it reached the zenith itself. Such
intensity of colouring is exceedingly rare in the Alps; and this fact,
together with the known variations in the intensity of the firmamental
blue, justify the conclusion that the colouring must, in a great
measure, be due to some _variable constituent_ of the atmosphere. If
_the air_ were competent to produce these magnificent effects they would
be the rule instead of the exception.
[Sidenote: FINISHED WORK. 1858.]
No sooner had the thermometers been thus disposed of than the weather
appeared to undergo a permanent change. On the 10th it was perfectly
fine--not the slightest mist upon Mont Blanc; on the 11th this was also
the case. Balmat still had the old thermometer to which I have already
referred; it might not do to show the minimum temperature of the air,
but it might show the temperature at a certain depth below the surface.
I find in my own case that the finishing of work has a great moral
value: work completed is a safe fulcrum for the performance of other
work; and even though in the course of our labours experience should
show us a better means of accomplishing a given end, it is often far
preferable to reach the end, even by defective means, than to swerve
from our course. The habits which this conviction had superinduced no
doubt influenced me when I decided on placing Balmat's thermometer on
the summit of Mont Blanc.
FOOTNOTES:
[A] I find with pleasure that my friend Mr. John Ball is now exerting
himself in this direction.
[B] The minimum temperature of the subsequent winter, as shown by this
thermometer, was -6° Fahr., or 38° below the freezing point. The
instrument placed in the ice was broken.
SECOND ASCENT OF MONT BLANC, 1858.
(25.)
[Sidenote: SHADOWS OF THE AIGUILLES. 1858.]
On the 12th of September, at 5-1/2 A.M. the sunbeams had already fallen
upon the mountain; but though the sky above him, and over the entire
range of the Aiguilles, was without a cloud, the atmosphere presented an
appearance of turbidity resembling that produced by the dust and thin
smoke mechanically suspended in a London atmosphere on a dry summer's
day. At 20 minutes past 7 we quitted Chamouni, bearing with us the good
wishes of a portion of its inhabitants.
[Sidenote: INTERFERENCE-SPECTRA. 1858.]
A lady accompanied us on horseback to the point where the path to the
Grands Mulets deviates from that to the Plan des Aiguilles; here she
turned to the left, and we proceeded slowly upwards, through woods of
pine, hung with fantastic lichens: escaping from the gloom of these, we
emerged upon slopes of bosky underwood, green hazel, and green larch,
with the red berries of the mountain-ash shining brightly between them.
Through the air above us, like gnomons of a vast sundial, the Aiguilles
cast their fanlike shadows, which moved round as the day advanced.
Slopes of rhododendrons with withered flowers next succeeded, but the
colouring of the bilberry-leaves was scarcely less exquisite than the
freshest bloom of the Alpine rose. For a long time we were in the cool
shadow of the mountain, catching, at intervals, through the twigs in
front of us, glimpses of the sun surrounded by coloured spectra. On one
occasion a brow rose in front of me; behind it was a lustrous space of
heaven, adjacent to the sun, which, however, was hidden behind the brow;
against this space the twigs and weeds upon the summit of the brow shone
as if they were self-luminous, while some bits of thistle-down floating
in the air appeared, where they crossed this portion of the heavens,
like fragments of the sun himself. Once the orb appeared behind a
rounded mass of snow which lay near the summit of the Aiguille du Midi.
Looked at with the naked eyes, it seemed to possess a billowy motion,
the light darting from it in dazzling curves,--a subjective effect
produced by the abnormal action of the intense light upon the eye. As
the sun's disk came more into view, its rays however still grazing the
summit of the mountain, interference-spectra darted from it on all
sides, and surrounded it with a glory of richly-coloured bars. Mingling
however with the grandeur of nature, we had the anger and obstinacy of
man. With a view to subsequent legal proceedings, the Guide Chef sent a
spy after us, who, having satisfied himself of our delinquency, took his
unpleasant presence from the splendid scene.
Strange to say, though the luminous appearance of bodies projected
against the sky adjacent to the rising sun is a most striking and
beautiful phenomenon, it is hardly ever seen by either guides or
travellers; probably because they avoid looking towards a sky the
brightness of which is painful to the eyes. In 1859 Auguste Balmat had
never seen the effect; and the only written description of it which we
possess is one furnished by Professor Necker, in a letter to Sir David
Brewster, which is so interesting that I do not hesitate to reproduce it
here:--
[Sidenote: PROFESSOR NECKER'S LETTER. 1858.]
"I now come to the point," writes M. Necker, "which you particularly
wished me to describe to you; I mean the luminous appearance of trees,
shrubs, and birds, when seen from the foot of a mountain a little before
sunrise. The wish I had to see again the phenomenon before attempting to
describe it made me detain this letter a few days, till I had a fine day
to go to see it at the Mont Salève; so yesterday I went there, and
studied the fact, and in elucidation of it I made a little drawing, of
which I give you here a copy: it will, with the explanation and the
annexed diagram (Fig. 9), impart to you, I hope, a correct idea of the
phenomenon. You must conceive the observer placed at the foot of a hill
interposed between him and the place where the sun is rising, and thus
entirely in the shade; the upper margin of the mountain is covered with
woods or detached trees and shrubs, which are projected as dark objects
on a very bright and clear sky, except at the very place where the sun
is just going to rise, for there all the trees and shrubs bordering the
margin are entirely,--branches, leaves, stem and all,--of a pure and
brilliant white, appearing extremely bright and luminous, although
projected on a most brilliant and luminous sky, as that part of it which
surrounds the sun always is. All the minutest details, leaves, twigs,
&c., are most delicately preserved, and you would fancy you saw these
trees and forests made of the purest silver, with all the skill of the
most expert workman. The swallows and other birds flying in those
particular spots appear like sparks of the most brilliant white.
Unfortunately, all these details, which add so much to the beauty of
this splendid phenomenon, cannot be represented in such small sketches.
[Illustration: Fig. 9. Luminous Trees projected against the sky at
sunrise.]
"Neither the hour of the day nor the angle which the object makes with
the observer appears to have any effect; for on some occasions I have
seen the phenomenon take place at a very early hour in the morning.
Yesterday it was 10 A.M., when I saw it as represented in Fig. 10. I saw
it again on the same day at 5 P.M., at a different place of the same
mountain, for which the sun was just setting. At one time the angle of
elevation of the lighted white shrubs above the horizon of the spectator
was about 20°, while at another place it was only 15°. But the extent of
the field of illumination is variable, according to the distance at
which the spectator is placed from it. When the object behind which the
sun is just going to rise, or has just been setting, is very near, no
such effect takes place. In the case represented in Fig. 9 the distance
was about 194 mètres, or 636 English feet, from the spectator in a
direct line, the height above his level being 60 mètres, or 197 English
feet, and the horizontal line drawn from him to the horizontal
projection of these points on the plane of his horizon being 160 mètres,
or 525 English feet, as will be seen in the following diagram, Fig. 10.
[Sidenote: SILVER TREES AT SUNRISE. 1858.]
[Illustration: Fig. 10. Luminous Trees projected against the sky at
sunrise.]
[Sidenote: BIRDS AS SPARKS OR STARS. 1858.]
"In this case only small shrubs and the lower half of the stem of a tree
are illuminated white, and the horizontal extent of this effect is also
comparatively small; while at other places when I was near the edge
behind which the sun was going to rise no such effect took place. But on
the contrary, when I have witnessed the phenomenon at a greater distance
and at a greater height, as I have seen it other times on the same and
on other mountains of the Alps, large tracts of forests and immense
spruce-firs were illuminated white throughout their whole length, as I
have attempted to represent in Fig. 11, and the corresponding diagram,
Fig. 12. Nothing can be finer than these silver-looking spruce-forests.
At the same time, though at a distance of more than a thousand mètres, a
vast number of large swallows or swifts (_Cypselus alpinus_), which
inhabit these high rocks, were seen as small brilliant stars or sparks
moving rapidly in the air. From these facts it appears to me obvious
that the extent of the illuminated spots varies in a direct ratio of
their distance; but at the same time that there must be a constant
angular space, corresponding probably to the zone, a few minutes of a
degree wide, around the sun's disk, which is a limit to the occurrence
of the appearance. This would explain how the real extent which it
occupies on the earth's surface varies with the relative distance of the
spot from the eye of the observer, and accounts also for the phenomenon
being never seen in the low country, where I have often looked for it in
vain. Now that you are acquainted with the circumstances of the fact, I
have no doubt you will easily observe it in some part or other of your
Scotch hills; it may be some long heather or furze will play the part
of our Alpine forests, and I would advise you to try and place a
bee-hive in the required position, and it would perfectly represent our
swallows, sparks, and stars."
[Illustration: Fig. 11. Luminous Trees projected against the sky at
sunrise.]
[Illustration: Fig. 12. Luminous Trees projected against the sky at
sunrise.]
[Sidenote: THE LADDER CONDEMNED. 1858.]
Our porters, with one exception, reached the Pierre à l'Echelle as soon
as ourselves; and here having refreshed themselves, and the due exchange
of loads having been made, we advanced upon the glacier, which we
crossed, until we came nearly opposite to the base of the Grands Mulets.
The existence of one wide crevasse, which was deemed impassable, had
this year introduced the practice of assailing the rocks at their base,
and climbing them to the cabin, an operation which Balmat wished to
avoid. At Chamouni, therefore, he had made inquiries regarding the width
of the chasm, and acting on his advice I had had a ladder constructed in
two pieces, which, united together by iron attachments, was supposed to
be of sufficient length to span the fissure. On reaching the latter, the
pieces were united, and the ladder thrown across, but the bridge was so
frail and shaky at the place of junction, and the chasm so deep, that
Balmat pronounced the passage impracticable.
[Sidenote: CROSSING CREVASSES. 1858.]
The porters were all grouped beside the crevasse when this announcement
was made, and, like hounds in search of the scent, the group instantly
broke up, seeking in all directions for a means of passage. The talk was
incessant and animating; attention was now called in one direction, anon
in another, the men meanwhile throwing themselves into the most
picturesque groups and attitudes. All eyes at length were directed upon
a fissure which was spanned at one point by an arch of snow, certainly
under two feet deep at the crown. A stout rope was tied round the waist
of one of our porters, and he was sent forward to test the bridge. He
approached it cautiously, treading down the snow to give it compactness,
and thus make his footing sure as he advanced; bringing regelation into
play, he gave the mass the necessary continuity, and crossed in safety.
The rope was subsequently stretched over the _pont_, and each of us
causing his right hand to slide along it, followed without accident.
Soon afterwards, however, we met with a second and very formidable
crevasse, to cross which we had but half of our ladder, which was
applied as follows:--The side of the fissure on which we stood was lower
than the opposite one; over the edge of the latter projected a cornice
of snow, and a ledge of the same material jutted from the wall of the
crevasse, a little below us. The ladder was placed from ledge to
cornice, both of its ends being supported by snow. I could hardly
believe that so frail a bearing could possibly support a man's weight;
but a porter was tied as before, and sent up the ladder, while we
followed protected by the rope. We were afterwards tied together, and
thus advanced in an orderly line to the Grands Mulets.
[Sidenote: GORGEOUS SUNSET. 1858.]
The cabin was wet and disagreeable, but the sunbeams fell upon the brown
rocks outside, and thither Mr. Wills and myself repaired to watch the
changes of the atmosphere. I took possession of the flat summit of a
prism of rock, where, lying upon my back, I watched the clouds forming,
and melting, and massing themselves together, and tearing themselves
like wool asunder in the air above. It was nature's language addressed
to the intellect; these clouds were visible symbols which enabled us to
understand what was going on in the invisible air. Here unseen currents
met, possessing different temperatures, mixing their contents both of
humidity and motion, producing a mean temperature unable to hold their
moisture in a state of vapour. The water-particles, obeying their mutual
attractions, closed up, and a visible cloud suddenly shook itself out,
where a moment before we had the pure blue of heaven. Some of the clouds
were wafted by the air towards atmospheric regions already saturated
with moisture, and along their frontal borders new cloudlets ever piled
themselves, while the hinder portions, invaded by a drier or a warmer
air, were dissipated; thus the cloud advanced, with gain in front and
loss behind, its permanence depending on the balance between them. The
day waned, and the sunbeams began to assume the colouring due to their
passage through the horizontal air. The glorious light, ever deepening
in colour, was poured bounteously over crags, and snows, and clouds, and
suffused with gold and crimson the atmosphere itself. I had never seen
anything grander than the sunset on that day. Clouds with their central
portions densely black, denying all passage to the beams which smote
them, floated westward, while the fiery fringes which bordered them were
rendered doubly vivid by contrast with the adjacent gloom. The smaller
and more attenuated clouds were intensely illuminated throughout. Across
other inky masses were drawn zigzag bars of radiance which resembled
streaks of lightning. The firmament between the clouds faded from a
blood-red through orange and daffodil into an exquisite green, which
spread like a sea of glory through which those magnificent argosies
slowly sailed. Some of the clouds were drawn in straight chords across
the arch of heaven, these being doubtless the sections of layers of
cloud whose horizontal dimensions were hidden from us. The cumuli around
and near the sun himself could not be gazed upon, until, as the day
declined, they gradually lost their effulgence and became tolerable to
the eyes. All was calm--but there was a wildness in the sky like that of
anger, which boded evil passions on the part of the atmosphere. The sun
at length sank behind the hills, but for some time afterwards carmine
clouds swung themselves on high, and cast their ruddy hues upon the
mountain snows. Duskier and colder waxed the west, colder and sharper
the breeze of evening upon the Grands Mulets, and as twilight deepened
towards night, and the stars commenced to twinkle through the chilled
air, we retired from the scene.
[Sidenote: STORM ON THE GRANDS MULETS. 1858.]
The anticipated storm at length gave notice of its coming. The
sea-waves, as observed by Aristotle, sometimes reach the shore before
the wind which produces them is felt; and here the tempest sent out its
precursors, which broke in detached shocks upon the cabin before the
real storm arrived. Billows of air, in ever quicker succession, rolled
over us with a long surging sound, rising and falling as crest succeeded
trough and trough succeeded crest. And as the pulses of a vibrating
body, when their succession is quick enough, blend to a continuous note,
so these fitful gusts linked themselves finally to a storm which made
its own wild music among the crags. Grandly it swelled, carrying the
imagination out of doors, to the clouds and darkness, to the loosened
avalanches and whirling snow upon the mountain heads. Moored to the rock
on two sides, the cabin stood firm, and its manifest security allowed
the mind the undisturbed enjoyment of the atmospheric war. We were
powerfully shaken, but had no fear of being uprooted; and a certain
grandeur of the heart rose responsive to the grandeur of the storm.
Mounting higher and higher, it at length reached its maximum strength,
from which it lowered fitfully, until at length, with a melancholy wail,
it bade our rock farewell.
A little before half-past one we issued from the cabin. The night being
without a moon, we carried three lanterns. The heavens were crowded with
stars, among which, however, angry masses of cloud here and there still
wandered. The storm, too, had left a rear-guard behind it; and strong
gusts rolled down upon us at intervals, at one time, indeed, so violent
as to cause Balmat to express doubts of our being able to reach the
summit. With a thick handkerchief bound around my hat and ears I enjoyed
the onset of the wind. Once, turning my head to the left, I saw what
appeared to me to be a huge mass of stratus cloud, at a great distance,
with the stars shining over it. In another instant a precipice of _névé_
loomed upon us; we were close to its base, and along its front the
annual layers were separated from each other by broad dark bands.
Through the gloom it appeared like a cloud, the lines of bedding giving
to it the stratus character.
[Sidenote: A COMET DISCOVERED. 1858.]
Immediately before lying down on the previous evening I had opened the
little window of the cabin to admit some air. In the sky in front of me
shone a curious nodule of misty light with a pale train attached to it.
In 1853, on the side of the Brocken, I had observed, without previous
notice, a comet discovered a few days previously by a former fellow
student, and here was another "discovery" of the same kind. I inspected
the stranger with my telescope, and assured myself that it was a comet.
Mr. Wills chanced to be outside at the time, and made the same
observation independently. As we now advanced up the mountain its
ominous light gleamed behind us, while high up in heaven to our left the
planet Jupiter burned like a lamp of intense brightness. The Petit
Plateau forms a kind of reservoir for the avalanches of the Dôme du
Goûter, and this year the accumulation of frozen débris upon it was
enormous. We could see nothing but the ice-blocks on which the light of
the lanterns immediately fell; we only knew that they had been
discharged from the _séracs_, and that similar masses now rose
threatening to our right, and might at any moment leap down upon us.
Balmat commanded silence, and urged us to move across the plateau with
all possible celerity. The warning of our guide, the wild and rakish
appearance of the sky, the spent projectiles at our feet, and the comet
with its "horrid hair" behind, formed a combination eminently calculated
to excite the imagination.
[Sidenote: DAWN ON THE GRAND PLATEAU. 1858.]
And now the sky began to brighten towards dawn, with that deep and calm
beauty which suggests the thought of adoration to the human mind. Helped
by the contemplation of the brightening east, which seemed to lend
lightness to our muscles, we cheerily breasted the steep slope up to the
Grand Plateau. The snow here was deep, and each of our porters took the
lead in turn. We paused upon the Grand Plateau and had breakfast;
digging, while we halted, our feet deeply into the snow. Thence up to
the corridor, by a totally different route from that pursued by Mr.
Hirst and myself the year previously; the slope was steep, but it had
not a precipice for its boundary. Deep steps were necessary for a time,
but when we reached the summit our ascent became more gentle. The
eastern sky continued to brighten, and by its illumination the Grand
Plateau and its bounding heights were lovely beyond conception. The snow
was of the purest white, and the glacier, as it pushed itself on all
sides into the basin, was riven by fissures filled with a coerulean
light, which deepened to inky gloom as the vision descended into them.
The edges were overhung with fretted cornices, from which depended long
clear icicles, tapering from their abutments like spears of crystal. The
distant fissures, across which the vision ranged obliquely without
descending into them, emitted that magical firmamental shimmer which,
contrasted with the pure white of the snow, was inexpressibly lovely.
Near to us also grand castles of ice reared themselves, some erect, some
overturned, with clear cut sides, striped by the courses of the annual
snows, while high above the _séracs_ of the plateau rose their still
grander brothers of the Dôme du Goûter. There was a nobility in this
glacier scene which I think I have never seen surpassed;--a strength of
nature, and yet a tenderness, which at once raised and purified the
soul. The gush of the direct sunlight could add nothing to this heavenly
beauty; indeed I thought its yellow beams a profanation as they crept
down from the humps of the Dromedary, and invaded more and more the
solemn purity of the realm below.
[Sidenote: BALMAT IN DANGER. 1858.]
Our way lay for a time amid fine fissures with blue walls, until at
length we reached the edge of one which elicited other sentiments than
those of admiration. It must be crossed. At the opposite side was a high
and steep bank of ice which prolonged itself downwards, and ended in a
dependent eave of snow which quite overhung the chasm, and reached to
within about a yard of our edge of the crevasse. Balmat came forward
with his axe, and tried to get a footing on the eave: he beat it gently,
but the axe went through the snow, forming an aperture through which the
darkness of the chasm was rendered visible. Our guide was quite free,
without rope or any other means of security; he beat down the snow so as
to form a kind of stirrup, and upon this he stepped. The stirrup gave
way, it was right over the centre of the chasm, but with wonderful tact
and coolness he contrived to get sufficient purchase from the yielding
mass to toss himself back to the side of the chasm. The rope was now
brought forward and tied round the waist of one of the porters; another
step was cautiously made in the eave of snow, the man was helped across,
and lessened his own weight by means of his hatchet. He gradually got
footing on the face of the steep, which he mounted by escaliers; and on
reaching a sufficient height he cut two large steps in which his feet
might rest securely. Here he laid his breast against the sloping wall,
and another person was sent forward, who drew himself up by the rope
which was attached to the leader. Thus we all passed, each of us in turn
bearing the strain of his successor upon the rope; it was our last
difficulty, and we afterwards slowly plodded through the snow of the
corridor towards the base of the Mur de la Côte.
[Sidenote: STORM ON MONT BLANC. 1858.]
[Sidenote: THERMOMETER BURIED. 1858.]
Climbing zigzag, we soon reached the summit of the Mur, and immediately
afterwards found ourselves in the midst of cold drifting clouds, which
obscured everything. They dissolved for a moment and revealed to us the
sunny valley of Chamouni; but they soon swept down again and completely
enveloped us. Upon the Calotte, or last slope, I felt no trace of the
exhaustion which I had experienced last year, but enjoyed free lungs and
a quiet heart. The clouds now whirled wildly round us, and the fine
snow, which was caught by the wind and spit bitterly against us, cut off
all visible communication between us and the lower world. As we
approached the summit the air thickened more and more, and the cold,
resulting from the withdrawal of the sunbeams, became intense. We
reached the top, however, in good condition, and found the new snow
piled up into a sharp _arête_, and the summit of a form quite different
from that of the _Dos d'un Ane_, which it had presented the previous
year. Leaving Balmat to make a hole for the thermometer, I collected a
number of bâtons, drove them into the snow, and, drawing my plaid round
them, formed a kind of extempore tent to shelter my boiling-water
apparatus. The covering was tightly held, but the snow was as fine and
dry as dust, and penetrated everywhere: my lamp could not be secured
from it, and half a box of matches was consumed in the effort to ignite
it. At length it did flame up, and carried on a sputtering combustion.
The cold of the snow-filled boiler condensing the vapour from the lamp
gradually produced a drop, which, when heavy enough to detach itself
from the vessel, fell upon the flame and put it out. It required much
patience and the expenditure of many matches to relight it. Meanwhile
the absence of muscular action caused the cold to affect our men
severely. My beard and whiskers were a mass of clotted ice. The bâtons
were coated with ice, and even the stem of my thermometer, the bulb of
which was in hot water, was covered by a frozen enamel. The clouds
whirled, and the little snow granules hit spitefully against the skin
wherever it was exposed. The temperature of the air was 20° Fahr. below
the freezing point. I was too intent upon my work to heed the cold much,
but I was numbed; one of my fingers had lost sensation, and my right
heel was in pain: still I had no thought of forsaking my observation
until Mr. Wills came to me and said that we must return speedily, for
Balmat's hands were _gelées_. I did not comprehend the full significance
of the word; but, looking at the porters, they presented such an aspect
of suffering that I feared to detain them longer. They looked like worn
old men, their hair and clothing white with snow, and their faces blue,
withered, and anxious-looking. The hole being ready, I asked Balmat for
the magnet to arrange the index of the thermometer: his hands seemed
powerless. I struck my tent, deposited the instrument, and, as I watched
the covering of it up, some of the party, among whom were Mr. Wills and
Balmat, commenced the descent.[A]
[Sidenote: BALMAT FROSTBITTEN. 1858.]
I followed them speedily. Midway down the Calotte I saw Balmat, who was
about a hundred yards in advance of me, suddenly pause and thrust his
hands into the snow, and commence rubbing them vigorously. The
suddenness of the act surprised me, but I had no idea at the time of its
real significance: I soon came up to him; he seemed frightened, and
continued to beat and rub his hands, plunging them, at quick intervals,
into the snow. Still I thought the thing would speedily pass away, for
I had too much faith in the man's experience to suppose that he would
permit himself to be seriously injured. But it did not pass as I hoped
it would, and the terrible possibility of his losing his hands presented
itself to me. He at length became exhausted by his own efforts,
staggered like a drunken man, and fell upon the snow. Mr. Wills and
myself took each a hand, and continued the process of beating and
rubbing. I feared that we should injure him by our blows, but he
continued to exclaim, "N'ayez pas peur, frappez toujours, frappez
fortement!" We did so, until Mr. Wills became exhausted, and a porter
had to take his place. Meanwhile Balmat pinched and bit his fingers at
intervals, to test their condition; but there was no sensation. He was
evidently hopeless himself; and, seeing him thus, produced an effect
upon me that I had not experienced since my boyhood--my heart swelled,
and I could have wept like a child. The idea that I should be in some
measure the cause of his losing his hands was horrible to me; schemes
for his support rushed through my mind with the usual swiftness of such
speculations, but no scheme could restore to him his lost hands. At
length returning sensation in one hand announced itself by excruciating
pain. "Je souffre!" he exclaimed at intervals--words which, from a man
of his iron endurance, had a more than ordinary significance. But pain
was better than death, and, under the circumstances, a sign of
improvement. We resumed our descent, while he continued to rub his hands
with snow and brandy, thrusting them at every few paces into the mass
through which we marched. At Chamouni he had skilful medical advice, by
adhering to which he escaped with the loss of six of his nails--his
hands were saved.
I cannot close this recital without expressing my admiration of the
dauntless bearing of our porters, and of the cheerful and efficient
manner in which they did their duty throughout the whole expedition.
Their names are Edouard Bellin, Joseph Favret, Michel Payot, Joseph
Folliguet, and Alexandre Balmat.
FOOTNOTES:
[A] In August, 1859, I found the temperature of water, boiling in an
open vessel at the summit of Mont Blanc, to be 184.95° Fahr. On that
occasion also, though a laborious search was made for the thermometer,
it could not be found.
(26.)
[Sidenote: PROCÈS-VERBAL. 1858.]
The hostility of the chief guide to the expedition was not diminished by
the letter of the Intendant; and he at once entered a _procès-verbal_
against Balmat and his companions on their return to Chamouni. I felt
that the power thus vested in an unlettered man to arrest the progress
of scientific observations was so anomalous, that the enlightened and
liberal Government of Sardinia would never tolerate such a state of
things if properly represented to it. The British Association met at
Leeds that year, and to it, as a guardian of science, my thoughts
turned. I accordingly laid the case before the Association, and obtained
its support: a resolution was unanimously passed "that application be
made to the Sardinian authorities for increased facilities for making
scientific observations in the Alps."
Considering the arduous work which Balmat had performed in former years
in connexion with the glaciers, and especially his zeal in determining,
under the direction of Professor Forbes, their winter motion--for which,
as in the case above recorded, he refused all personal remuneration--I
thought such services worthy of some recognition on the part of the
Royal Society. I suggested this to the Council, and was met by the same
cordial spirit of co-operation which I had previously experienced at
Leeds. A sum of five-and-twenty guineas was at once voted for the
purchase of a suitable testimonial; and a committee, consisting of Sir
Roderick Murchison, Professor Forbes, and myself, was appointed to
carry the thing out. Balmat was consulted, and he chose a photographic
apparatus, which, with a suitable inscription, was duly presented to
him.
[Sidenote: BRITISH ASSOCIATION. 1858.]
Thus fortified, I drew up an account of what had occurred at Chamouni
during my last visit, accompanied by a brief statement of the changes
which seemed desirable. This was placed in the hands of the President of
the British Association, to whose prompt and powerful co-operation in
this matter every Alpine explorer who aspires to higher ground than
ordinary is deeply indebted. The following letter assured me that the
facility applied for by the British Association would be granted by the
Sardinian Government, and that future men of science would find in the
Alps a less embarrassed field of operations than had fallen to my lot in
the summer of 1858.
[Sidenote: THE PRESIDENT'S LETTER. 1858.]
"12, Hertford-street, Mayfair, W.,
"February 18th, 1859.
"My dear Sir,--
"Having, as I informed you in my last note, communicated with
the Sardinian Minister Plenipotentiary the day after receiving
your statement relative to the guides at Chamouni, I have been
favoured by replies from the Minister, of the 4th and 17th
February. In the first the Marquis d'Azeglio assures me that he
will bring the subject before the competent authorities at
Turin, accompanying the transmission 'd'une récommandation
toute spéciale.' In the second letter the Marquis informs me
that 'the preparation of new regulations for the guides at
Chamouni had for some time occupied the attention of the
Minister of the Interior, and that these regulations will be in
rigorous operation, in all probability, at the commencement of
the approaching summer.' The Marquis adds that, 'as the
regulations will be based upon a principle of much greater
liberty, he has every reason to believe that they will satisfy
all the desires of travellers in the interests of science.'
"With much pleasure at the opportunity of having been in any
degree able to bring about the fulfilment of your wishes on the
subject,
"I remain, my dear Sir,
"Faithfully yours,
"RICHARD OWEN.
"Pres. Brit. Association.
"Prof. Tyndall, F.R.S."
It ought to be stated that, previous to my arrival at Chamouni in 1858,
an extremely cogent memorial drawn up by Mr. John Ball had been
presented to the Marquis d'Azeglio by a deputation from the Alpine Club.
It was probably this memorial which first directed the attention of the
Sardinian Minister of the Interior to the subject.
WINTER EXPEDITION TO THE MER DE GLACE, 1859.
(27.)
Having ten days at my disposal last Christmas, I was anxious to employ
them in making myself acquainted with the winter aspects and phenomena
of the Mer de Glace. On Wednesday, the 21st of December, I accordingly
took my place to Paris, but on arriving at Folkestone found the sea so
tempestuous that no boat would venture out.
[Sidenote: FIRST DEFEAT, AND FRESH ATTEMPT. 1859.]
The loss of a single day was more than I could afford, and this failure
really involved the loss of two. Seeing, therefore, the prospect of any
practical success so small, I returned to London, purposing to give the
expedition up. On the following day, however, the weather lightened, and
I started again, reaching Paris on Friday morning. On that day it was
not possible to proceed beyond Macon, where, accordingly, I spent the
night, and on the following day reached Geneva.
Much snow had fallen; at Paris it still cumbered the streets, and round
about Macon it lay thick, as if a more than usually heavy cloud had
discharged itself on that portion of the country. Between Macon and
Roussillon it was lighter, but from the latter station onwards the
quantity upon the ground gradually increased.
[Sidenote: GENEVA TO CHAMOUNI. 1859.]
On Christmas morning, at 8 o'clock, I left Geneva by the diligence for
Sallenches. The dawn was dull, but the sky cleared as the day advanced,
and finally a dome of cloudless blue stretched overhead. The mountains
were grand; their sunward portions of dazzling whiteness, while the
shaded sides, in contrast with the blue sky behind them, presented a
ruddy, subjective tint. The brightness of the day reached its maximum
towards one o'clock, after which a milkiness slowly stole over the
heavens, and increased in density until finally a drowsy turbidity
filled the entire air. The distant peaks gradually blended with the
white atmosphere above them and lost their definition. The black pine
forests on the slopes of the mountains stood out in strong contrast to
the snow; and, when looked at through the spaces enclosed by the tree
branches at either side of the road, they appeared of a decided
indigo-blue. It was only when thus detached by a vista in front that the
blue colour was well seen, the air itself between the eye and the
distant pines being the seat of the colour. Goethe would have regarded
it as an excellent illustration of his 'Farbenlehre.'
We reached Sallenches a little after 4 P.M., where I endeavoured to
obtain a sledge to continue my journey. A fit one was not to be found,
and a carriage was therefore the only resort. We started at five; it was
very dark, but the feeble reflex of the snow on each side of the road
was preferred by the postilion to the light of lamps. Unlike the
enviable ostrich, I cannot shut my eyes to danger when it is near: and
as the carriage swayed towards the precipitous road side, I could not
fold myself up, as it was intended I should, but, quitting the interior
and divesting my limbs of every encumbrance, I took my seat beside the
driver, and kept myself in readiness for the spring, which in some cases
appeared imminent. My companion however was young, strong, and
keen-eyed; and though we often had occasion for the exercise of the
quality last mentioned, we reached Servoz without accident.
[Sidenote: DESOLATION. 1859.]
[Sidenote: A HORSE IN THE SNOW. 1859.]
Here we baited, and our progress afterwards was slow and difficult. The
snow on the road was deep and hummocky, and the strain upon the horses
very great. Having crossed the Arve at the Pont-Pelissier, we both
alighted, and I went on in advance. The air was warm, and not a whisper
disturbed its perfect repose. There was no moon, and the heavy clouds,
which now quite overspread the heavens, cut off even the feeble light of
the stars. The sound of the Arve, as it rushed through the deep valley
to my left, came up to me through crags and trees with a sad murmur.
Sometimes on passing an obstacle, the sound was entirely cut off, and
the consequent silence was solemn in the extreme. It was a churchyard
stillness, and the tall black pines, which at intervals cast their
superadded gloom upon the road, seemed like the hearse-plumes of a dead
world. I reached a wooden hut, where a lame man offers bâtons, minerals,
and _eau de vie_, to travellers in summer. It was forsaken, and half
buried in the snow. I leaned against the door, and enjoyed for a time
the sternness of the surrounding scene. My conveyance was far behind,
and the intermittent tinkle of the horses' bells, which augmented
instead of diminishing the sense of solitude, informed me of the
progress and the pauses of the vehicle. At the summit of the road I
halted until my companion reached me; we then both remounted, and
proceeded slowly towards Les Ouches. We passed some houses, the aspect
of which was even more dismal than that of Nature; their roofs were
loaded with snow, and white buttresses were reared against the walls.
There was no sound, no light, no voice of joy to indicate that it was
the pleasant Christmas time. We once met the pioneer of a party of four
drunken peasants: he came right against us, and the coachman had to pull
up. Planting his feet in the snow and propping himself against the
leader's shoulder, the bacchanal exhorted the postilion to drive on; the
latter took him at his word, and overturned him in the snow. After this
we encountered no living thing. The horses seemed seized by a kind of
torpor, and leaned listlessly against each other; vainly the postilion
endeavoured to rouse them by word and whip; they sometimes essayed to
trot down the slopes, but immediately subsided to their former
monotonous crawl. As we ascended the valley, the stillness of the air
was broken at intervals by wild storm-gusts, sent down against us from
Mont Blanc himself. These chilled me, so I quitted the carriage, and
walked on. Not far from Chamouni, the road, for some distance, had been
exposed to the full action of the wind, and the snow had practically
erased it. Its left wall was completely covered, while a few detached
stones, rising here and there above the surface, were the only
indications of the presence and direction of the right-hand wall. I
could not see the state of the surface, but I learned by other means
that the snow had been heaped in oblique ridges across my path. I
staggered over four or five of these in succession, sinking knee-deep,
and finally found myself immersed to the waist. This made me pause; I
thought I must have lost the road, and vainly endeavoured to check
myself by the positions of surrounding objects. I turned back and met
the carriage: it had stuck in one of the ridges; one horse was down, his
hind legs buried to the haunches, his left fore leg plunged to the
shoulder in snow, and the right one thrown forward upon the surface.
_C'est bien la route?_ demanded my companion. I went back exploring, and
assured myself that we were over the road; but I recommended him to
release the horses and leave the carriage to its fate. He, however,
succeeding in extricating the leader, and while I went on in advance
seeking out the firmer portions of the road, he followed, holding his
horses by their heads; and half an hour's struggle of this kind brought
us to Chamouni.
[Sidenote: CHAMOUNI ON CHRISTMAS NIGHT. 1859.]
It also was a little "city of the dead." There was no living thing in
the streets, and neither sound nor light in the houses. The fountain
made a melancholy gurgle, one or two loosened window-shutters creaked
harshly in the wind, and banged against the objects which limited their
oscillations. The Hôtel de l'Union, so bright and gay in summer, was
nailed up and forsaken; and the cross in front of it, stretching its
snow-laden arms into the dim air, was the type of desolation. We rang
the bell at the Hôtel Royal, but the bay of a watch-dog resounding
through the house was long our only reply. The bell appeared powerless
to wake the sleepers, and its sound mingled dismally with that of the
wind howling through the deserted passages. The noise of my boot-heel,
exerted long on the front door, was at length effective; it was
unbarred, and the physical heat of a good stove soon added itself to the
warmth of the welcome with which my hostess greeted me.
December 26th.--The snow fell heavily, at frequent intervals, throughout
the entire day. Dense clouds draped all the mountains, and there was not
the least prospect of my being able to see across the Mer de Glace. I
walked out alone in the dim light, and afterwards traversed the streets
before going to bed. They were quite forsaken. Cold and sullen the Arve
rolled under its wooden bridge, while the snow fell at intervals with
heavy shock from the roofs of the houses, the partial echoes from the
surfaces of the granules combining to render the sound loud and hollow.
Thus were the concerns of this little hamlet changed and fashioned by
the obliquity of the earth's axis, the chain of dependence which runs
throughout creation, linking the roll of a planet alike with the
interests of marmots and of men.
[Sidenote: ASCENT OF THE MOUNTAIN. 1859.]
[Sidenote: SNOW ON THE PINES. 1859.]
Tuesday, 27th December.--I rose at six o'clock, having arranged with my
men to start at seven, if the weather at all permitted. Edouard Simond,
my old assistant of 1857, and Joseph Tairraz were the guides of the
party; the porters were Edouard Balmat, Joseph Simond (fils d'Auguste),
François Ravanal, and another. They came at the time appointed; it was
snowing heavily, and we agreed to wait till eight o'clock and then
decide. They returned at eight, and finding them disposed to try the
ascent to the Montanvert, it was not my place to baulk them. Through the
valley the work was easy, as the snow had been partially beaten down,
but we soon passed the habitable limits, and had to break ground for
ourselves. Three of my men had tried to reach the Montanvert by _la
Filia_ on the previous Thursday, but their experience of the route had
been such as to deter them from trying it again. We now chose the
ordinary route, breasting the slope until we reached the cluster of
chalets, under the projecting eave of one of which the men halted and
applied "pattens" to their feet. These consisted of planks about sixteen
inches long and ten wide, which were firmly strapped to the feet. My
first impression was that they were worse than useless, for though they
sank less deeply than the unarmed feet, on being raised they carried
with them a larger amount of snow, which, with the leverage of the leg,
appeared to necessitate an enormous waste of force. I stated this
emphatically, but the men adhered to their pattens, and before I reached
the Montanvert I had reason to commend their practice as preferable to
my theory. I was however guided by the latter, and wore no pattens. The
general depth of the snow along the track was over three feet; the
footmarks of the men were usually rigid enough to bear my weight, but in
many cases I went through the crust which their pressure had produced,
and sank suddenly in the mass. The snow became softer as we ascended,
and my immersions more frequent, but the work was pure enjoyment, and
the scene one of extreme beauty. The previous night's snow had descended
through a perfectly still atmosphere, and had loaded all the branches of
the pines; the long arms of the trees drooped under the weight, and
presented at their extremities the appearance of enormous talons turned
downwards. Some of the smaller and thicker trees were almost entirely
covered, and assumed grotesque and beautiful forms; the upper part of
one in particular resembled a huge white parrot with folded wings and
drooping head, the slumber of the bird harmonizing with the torpor of
surrounding nature. I have given a sketch of it in Fig. 13.
[Illustration: Fig. 13. Snow on the Pines.]
[Sidenote: SOUND OF BREAKING SNOW. 1859.]
Previous to reaching the half-way spring, where the peasant girls offer
strawberries to travellers in summer, we crossed two large couloirs
filled with the débris of avalanches which had fallen the night before.
Between these was a ridge forty or fifty yards wide on which the snow
was very deep, the slope of the mountain also adding a component to the
fair thickness of the snow. My shoulder grazed the top of the embankment
to my right as I crossed the ridge, and once or twice I found myself
waist deep in a vertical shaft from which it required a considerable
effort to escape. Suddenly we heard a deep sound resembling the dull
report of a distant gun, and at the same moment the snow above us broke
across, forming a fissure parallel to our line of march. The layer of
snow had been in a state of strain, which our crossing brought to a
crisis: it gave way, but having thus relieved itself it did not descend.
Several times during the ascent the same phenomenon occurred. Once,
while engaged upon a very steep slope, one of the men cried out to the
leader, "_Arrêtez!_" Immediately in front of the latter the snow had
given way, forming a zigzag fissure across the slope. We all paused,
expecting to see an avalanche descend. Tairraz was in front; he struck
the snow with his bâton to loosen it, but seeing it indisposed to
descend he advanced cautiously across it, and was followed by the
others. I brought up the rear. The steepness of the mountain side at
this place, and the absence of any object to which one might cling,
would have rendered a descent with the snow in the last degree perilous,
and we all felt more at ease when a safe footing was secured at the
further side of the incline.
At the spring, which showed a little water, the men paused to have a
morsel of bread. The wind had changed, the air was clearing, and our
hopes brightening. As we ascended the atmosphere went through some
extraordinary mutations. Clouds at first gathered round the Aiguille and
Dôme du Goûter, casting the lower slopes of the mountain into intense
gloom. After a little time all this cleared away, and the beams of the
sun striking detached pieces of the slopes and summits produced an
extraordinary effect. The Aiguille and Dôme were most singularly
illumined, and to the extreme left rose the white conical hump of the
Dromedary, from which a long streamer of snow-dust was carried southward
by the wind. The Aiguille du Dru, which had been completely mantled
during the earlier part of the day, now threw off its cloak of vapour
and rose in most solemn majesty before us; half of its granite cone was
warmly illuminated, and half in shadow. The wind was high in the upper
regions, and, catching the dry snow which rested on the asperities and
ledges of the Aiguille, shook it out like a vast banner in the air. The
changes of the atmosphere, and the grandeur which they by turns revealed
and concealed, deprived the ascent of all weariness. We were usually
flanked right and left by pines, but once between the fountain and the
Montanvert we had to cross a wide unsheltered portion of the mountain
which was quite covered with the snow of recent avalanches. This was
lumpy and far more coherent than the undisturbed snow. We took advantage
of this, and climbed zigzag over the avalanches for three-quarters of an
hour, thus reaching the opposite pines at a point considerably higher
than the path. This, though not the least dangerous, was the least
fatiguing part of the ascent.
[Sidenote: COLOUR OF SNOW. 1859.]
I frequently examined the colour of the snow: though fresh, its blue
tint was by no means so pronounced as I have seen it on other occasions;
still it was beautiful. The colour is, no doubt, due to the optical
reverberations which occur within a fissure or cavity formed in the
snow. The light is sent from side to side, each time plunging a little
way into the mass; and being ejected from it by reflection, it thus
undergoes a sifting process, and finally reaches the eye as blue light.
The presence of any object which cuts off this cross-fire of the light
destroys the colour. I made conical apertures in the snow, in some cases
three feet deep, a foot wide at the mouth, and tapering down to the
width of my bâton. When the latter was placed along the axis of such a
cone, the blue light which had previously filled the cavity disappeared;
on the withdrawal of the bâton it was followed by the light, and thus by
moving the staff up and down its motions were followed by the alternate
appearance and extinction of the light. I have said that the holes made
in the snow seemed filled with a blue light, and it certainly appeared
as if the air contained in the cavities had itself been coloured, and
thereby rendered visible, the vision plunging into it as into a blue
medium. Another fact is perhaps worth notice: snow rarely lies so smooth
as not to present little asperities at its surface; little ridges or
hillocks, with little hollows between them. Such small hollows resemble,
in some degree, the cavities which I made in the snow, and from them, in
the present instance, a delicate light was sent to the eye, faintly
tinted with the pure blue of the snow-crystals. In comparison with the
spots thus illuminated, the little protuberances were gray. The portions
most exposed to the light seemed least illuminated, and their defect in
this respect made them appear as if a light-brown dust had been strewn
over them.
[Sidenote: THE MONTANVERT IN WINTER. 1859.]
After five hours and a half of hard work we reached the Montanvert. I
had often seen it with pleasure. Often, having spent the day alone amid
the _séracs_ of the Col du Géant, on turning the promontory of
Trélaporte on my way home, the sight of the little mansion has gladdened
me, and given me vigour to scamper down the glacier, knowing that
pleasant faces and wholesome fare were awaiting me. This day, also, the
sight of it was most welcome, despite its desolation. The wind had swept
round the auberge, and carried away its snow-buttresses, piling the mass
thus displaced against the adjacent sheds, to the roofs of which one
might step from the surface of the snow. The floor of the little château
in which I lodged in 1857 was covered with snow, and on it were the
fresh footmarks of a little animal--a marmot might have made such marks,
had not the marmots been all asleep--what the creature was I do not
know.
[Sidenote: CRYSTAL CURTAIN. 1859.]
In the application of her own principles, Nature often transcends the
human imagination; her acts are bolder than our predictions. It is thus
with the motion of glaciers; it was thus at the Montanvert on the day
now referred to. The floors, even where the windows appeared well
closed, were covered with a thin layer of fine snow; and some of the
mattresses in the bedrooms were coated to the depth of half an inch with
this fine powder. Given a chink through which the finest dust can pass,
dry snow appears competent to make its way through the same fissure. It
had also been beaten against the windows, and clung there like a ribbed
drapery. In one case an effect so singular was exhibited, that I doubted
my eyes when I first saw it. In front of a large pane of glass, and
quite detached from it, save at its upper edge, was a festooned curtain
formed entirely of minute ice-crystals. It appeared to be as fine as
muslin; the ease of its curves and the depth of its folds being such as
could not be excelled by the intentional arrangement of ordinary gauze.
The frost-figures on some of the window-panes were also of the most
extraordinary character: in some cases they extended over large spaces,
and presented the appearance which we often observe in London; but on
other panes they occurred in detached clusters, or in single flowers,
these grouping themselves together to form miniature bouquets of
inimitable beauty. I placed my warm hand against a pane which was
covered by the crystallization, and melted the frostwork which clung to
it. I then withdrew my hand and looked at the film of liquid through a
pocket-lens. The glass cooled by contact with the air, and after a time
the film commenced to move at one of its edges; atom closed with atom,
and the motion ran in living lines through the pellicle, until finally
the entire film presented the beauty and delicacy of an organism. The
connexion between such objects and what we are accustomed to call the
feelings may not be manifest, but it is nevertheless true that, besides
appealing to the pure intellect of man, these exquisite productions can
also gladden his heart and moisten his eyes.
[Sidenote: THE MER DE GLACE IN WINTER. 1859.]
The glacier excited the admiration of us all: not as in summer, shrunk
and sullied like a spent reptile, steaming under the influence of the
sun; its frozen muscles were compact, strength and beauty were
associated in its aspect. At some places it was pure and smooth; at
others frozen fins arose from it, high, steep, and sharply crested. Down
the opposite mountain side arrested streams set themselves erect in
successive terraces, the fronts of which were fluted pillars of ice.
There was no sound of water; even the Nant Blanc, which gushes from a
spring, and which some describe as permanent throughout the winter,
showed no trace of existence. From the Montanvert to Trélaporte the Mer
de Glace was all in shadow; but the sunbeams pouring down the corridor
of the Géant ruled a beam of light across the glacier at its upper
portion, smote the base of the Aiguille du Moine, and flooded the
mountain with glory to its crest. At the opposite side of the valley was
the Aiguille du Dru, with a banneret of snow streaming from its mighty
cone. The Grande Jorasse, and the range of summits between it and the
Aiguille du Géant, were all in view, and the Charmoz raised its
precipitous cliffs to the right, and pierced with its splinter-like
pinnacles the clear cold air. As the night drew on, the mountains seemed
to close in upon us; and on looking out before retiring to rest, a scene
so solemn had never before presented itself to my eyes or affected my
imagination.
[Sidenote: THE FIRST NIGHT. 1859.]
My men occupied the afternoon of the day of our arrival in making a
preliminary essay upon the glacier while I prepared my instruments. To
the person whom I intended to fix my stations, three others were
attached by sound ropes of considerable length. Hidden crevasses we
knew were to be encountered, and we had made due preparation for them.
Throughout the afternoon the weather remained fine, and at night the
stars shone out, but still with a feeble lustre. I could notice a
turbidity gathering in the air over the range of the Brévent, which
seemed disposed to extend itself towards us. At night I placed a chair
in the middle of the snow, at some distance from the house, and laid on
it a registering thermometer. A bountiful fire of pine logs was made in
the _salle à manger_; a mattress was placed with its foot towards the
fire, its middle line bisecting the right angle in which the fireplace
stood; this being found by experiment to be the position in which the
draughts from the door and from the windows most effectually neutralized
each other. In this region of calms I lay down, and covering myself with
blankets and duvets, listened to the crackling of the logs, and watched
their ruddy flicker upon the walls, until I fell asleep.
The wind rose during the night, and shook the windows: one pane in
particular seemed set in unison to the gusts, and responded to them by a
loud and melodious vibration. I rose and wedged it round with _sous_ and
penny pieces, and thus quenched its untimely music.
December 28th.--We were up before the dawn. Tairraz put my fire in
order, and I then rose. The temperature of the room at a distance of
eight feet from the fire was two degrees of Centigrade below zero; the
lowest temperature outside was eleven degrees of Centigrade below
zero,--not at all an excessive cold. The clouds indeed had, during the
night, thrown vast diaphragms across the sky, and thus prevented the
escape of the earth's heat into space.
While my assistants were preparing breakfast I had time to inspect the
glacier and its bounding heights. On looking up the Mer de Glace, the
Grande Jorasse meets the view, rising in steep outline from the wall of
cliffs which terminates the Glacier de Léchaud. Behind this steep
ascending ridge, which is shown on the frontispiece, and upon it, a
series of clouds had ranged themselves, stretching lightly along the
ridge at some places, and at others collecting into ganglia. A string of
rosettes was thus formed which were connected together by gauzy
filaments. The portion of the heavens behind the ridge was near the
domain of the rising sun, and when he cleared the horizon his red light
fell upon the clouds, and ignited them to ruddy flames. Some of the
lighter clouds doubled round the summit of the mountain, and swathed its
black crags with a vestment of transparent red. The adjacent sky wore a
strange and supernatural air; indeed there was something in the whole
scene which baffled analysis, and the words of Tennyson rose to my lips
as I gazed upon it:--
[Sidenote: A "ROSE OF DAWN." 1859.]
"God made Himself an awful rose of dawn."
I have spoken several times of the cloud-flag which the wind wafted from
the summit of the Aiguille du Dru. On the present occasion this grand
banner reached extraordinary dimensions. It was brindled in some places
as if whipped into curds by the wind; but through these continuous
streamers were drawn, which were bent into sinuosities resembling a
waving flag at a mast-head. All this was now illuminated with the sun's
red rays, which also fringed with fire the exposed edges and pinnacles
both of the Aiguille du Dru and the Aiguille Verte. Thus rising out of
the shade of the valley the mountains burned like a pair of torches, the
flames of which were blown half a mile through the air. Soon afterwards
the summits of the Aiguilles Rouges were illuminated, and day declared
itself openly among the mountains.
[Sidenote: THE STAKES FIXED. 1859.]
But these red clouds of the morning, magnificent though they were,
suggested thoughts which tended to qualify the pleasure which they gave:
they did not indicate good weather. Sometimes, indeed, they had to fight
with denser masses, which often prevailed, swathing the mountains in
deep neutral tint, but which, again yielding, left the glory of the
sunrise augmented by contrast with their gloom. Between eight and nine
A.M. we commenced the setting out of our first line, one of whose
termini was a point about a hundred yards higher up than the Montanvert
hotel; a withered pine on the opposite mountain side marking the other
terminus. The stakes made use of were four feet long. With the selfsame
bâton which I had employed upon the Mer de Glace in 1857, and which
Simond had preserved, the worthy fellow now took up the line. At some
places the snow was very deep, but its lower portions were sufficiently
compact to allow of a stake being firmly fixed in it. At those places
where the wind had removed the snow or rendered it thin, the ice was
pierced with an auger and the stake driven into it. The greatest caution
was of course necessary on the part of the men; they were in the midst
of concealed crevasses, and sounding was essential at every step. By
degrees they withdrew from me, and approached the eastern boundary of
the glacier, where the ice was greatly dislocated, and the labour of
wading through the snow enormous. Long détours were sometimes necessary
to reach a required point; but they were all accomplished, and we at
length succeeded in fixing eleven stakes along this line, the most
distant of which was within about eighty yards of the opposite side of
the glacier.
[Sidenote: STORM ON THE GLACIER. 1859.]
The men returned, and I consulted them as to the possibility of getting
a line across at the _Ponts_; but this was judged to be impossible in
the time. We thought, however, that a second line might be staked out at
some distance below the Montanvert. I took the theodolite down the
mountain-slope, wading at times breast-deep in snow, and having
selected a line, the men tied themselves together as before, and
commenced the staking out. The work was slowly but steadily and
steadfastly done. The air darkened; angry clouds gathered around the
mountains, and at times the glacier was swept by wild squalls. The men
were sometimes hidden from me by the clouds of snow which enveloped
them, but between those intermittent gusts there were intervals of
repose, which enabled us to prosecute our work. This line was more
difficult than the first one; the glacier was broken into sharp-edged
chasms; the ridges to be climbed were steep, and the snow which filled
the depressions profound. The oblique arrangement of the crevasses also
magnified the labour by increasing the circuits. I saw the leader of the
party often shoulder-deep in snow, treading the soft mass as a swimmer
walks in water, and I felt a wish to be at his side to cheer him and to
share his toil. Each man there, however, knew my willingness to do this
if occasion required it, and wrought contented. At length the last stake
being fixed, the faces of the men were turned homeward. The evening
became wilder, and the storm rose at times to a hurricane. On the more
level portions of the glacier the snow lay deep and unsheltered; among
its frozen waves and upon its more dislocated portions it had been
partially engulfed, and the residue was more or less in shelter. Over
the former spaces dense clouds of snow rose, whirling in the air and
cutting off all view of the glacier. The whole length of the Mer de
Glace was thus divided into clear and cloudy segments, and presented an
aspect of wild and wonderful turmoil. A large pine stood near me, with
its lowest branch spread out upon the surface of the snow; on this
branch I seated myself, and, sheltered by the trunk, waited until I saw
my men in safety. The wind caught the branches of the trees, shook down
their loads of snow, and tossed it wildly in the air. Every mountain
gave a quota to the storm. The scene was one of most impressive
grandeur, and the moan of the adjacent pines chimed in noble harmony
with the picture which addressed the eyes.
At length we all found ourselves in safety within doors. The windows
shook violently. The tempest was however intermittent throughout, as if
at each effort it had exhausted itself, and required time to recover its
strength. As I heard its heralding roar in the gullies of the mountains,
and its subsequent onset against our habitation, I thought wistfully of
my stations, not knowing whether they would be able to retain their
positions in the face of such a blast. That night however, as if the
storm had sung our lullaby, we all slept profoundly, having arranged to
commence our measurements as early as light permitted on the following
day.
[Sidenote: HEAVY SNOW. 1859.]
Thursday, 29th December.--"Snow, heavy snow: it must have descended
throughout the entire night; the quantity freshly fallen is so great;
the atmosphere at seven o'clock is thick with the descending flakes." At
eight o'clock it cleared up a little, and I proceeded to my station,
while the men advanced upon the glacier; but I had scarcely fixed my
theodolite when the storm recommenced. I had a man to clear away the
snow and otherwise assist me; he procured an old door from the hotel,
and by rearing it upon its end sheltered the object-glass of the
instrument. Added to the flakes descending from the clouds was the
spitting snow-dust raised by the wind, which for a time so blinded me
that I was unable to see the glacier. The measurement of the first stake
was very tedious, but practice afterwards enabled me to take advantage
of the brief lulls and periods of partial clearness with which the storm
was interfused.
[Sidenote: A MAN IN A CREVASSE. 1859.]
At nine o'clock my telescope happened to be directed upon the men as
they struggled through the snow; all evidence of the deep track which
they had formed yesterday having been swept away. I saw the leader sink
and suddenly disappear. He had stood over a concealed fissure, the roof
of which had given way and he had dropped in. I observed a rapid
movement on the part of the remaining three men: they grouped themselves
beside the fissure, and in a moment the missing man was drawn from
between its jaws. His disappearance and reappearance were both
extraordinary. We had, as I have stated, provided for contingencies of
this kind, and the man's rescue was almost immediate.
[Sidenote: SIX-RAYED CRYSTALS. 1859.]
My attendant brought two poles from the hotel which we thrust obliquely
into the snow, causing the free ends to cross each other; over these a
blanket was thrown, behind which I sheltered myself from the storm as
the men proceeded from stake to stake. At 9.30 the storm was so thick
that I was unable to see the men at the stake which they had reached at
the time; the flakes sped wildly in their oblique course across the
field of the telescope. Some time afterwards the air became quite still,
and the snow underwent a wonderful change. Frozen flowers similar to
those I had observed on Monte Rosa fell in myriads. For a long time the
flakes were wholly composed of these exquisite blossoms entangled
together. On the surface of my woollen dress they were soft as down; the
snow itself on which they fell seemed covered by a layer of down; while
my coat was completely spangled with six-rayed stars. And thus prodigal
Nature rained down beauty, and had done so here for ages unseen by man.
And yet some flatter themselves with the idea that this world was
planned with strict reference to human use; that the lilies of the field
exist simply to appeal to the sense of the beautiful in man. True, this
result is secured, but it is one of a thousand all equally important in
the eyes of Nature. Whence those frozen blossoms? Why for æons wasted?
The question reminds one of the poet's answer when asked whence was the
Rhodora:--
"Why wert thou there, O rival of the rose?
I never thought to ask, I never knew;
But in my simple ignorance suppose
The selfsame power that brought me there brought you!"[A]
I sketched some of the crystals, but, instead of reproducing these
sketches, which were rough and hasty, I have annexed two of the forms
drawn with so much skill and patience by Mr. Glaisher.
[Illustration: Fig. 14. Snow Crystals.]
[Illustration: Fig. 15. Snow Crystals.]
We completed the measurement of the first line before eleven o'clock,
and I felt great satisfaction in the thought that I possessed something
of which the weather could not deprive me. As I closed my note-book and
shifted the instrument to the second station, I felt that my expedition
was already a success.
At a quarter past eleven I had my theodolite again fixed, and ranging
the telescope along the line of pickets, I saw them all standing.
Crossing the ice wilderness, and suggesting the operation of
intelligence amid that scene of desolation, their appearance was
pleasant to me. Just before I commenced, a solitary jay perched upon the
summit of an adjacent pine and watched me. The air was still at the
time, and the snow fell heavily. The flowers moreover were magnificent,
varying from about the twentieth of an inch to two lines in diameter,
while, falling through the quiet air, their forms were perfect. Adjacent
to my theodolite was a stump of pine, from which I had the snow removed,
in order to have something to kick my toes against when they became
cold; and on the stump was placed a blanket to be used as a screen in
case of need. While I remained at the station a layer of snow an inch
thick fell upon this blanket, the whole layer being composed of these
exquisite flowers. The atmosphere also was filled with them. From the
clouds to the earth Nature was busy marshalling her atoms, and putting
to shame by the beauty of her structures the comparative barbarities of
Art.
[Sidenote: SOUND THROUGH THE SNOW-STORM. 1859.]
My men at length reached the first station, and the measurement
commenced. The storm drifted up the valley, thickening all the air as it
approached. Denser and denser the flakes fell; but still, with care and
tact I was able to follow my party to a distance of 800 yards. I had not
thought it possible to see so far through so dense a storm. At this
distance also my voice could be heard, and my instructions understood;
for once, as the man who took up the line stood behind his bâton and
prevented its projection against the white snow, I called out to him to
stand aside, and he promptly did so. Throughout the entire measurement
the snow never ceased falling, and some of the illusions which it
produced were extremely singular. The distant boundary of the glacier
appeared to rise to an extraordinary height, and the men wading through
the snow appeared as if climbing up a wall. The labour along this line
was still greater than on the former; on the steeper slopes especially
the toil was great; for here the effort of the leader to lift his own
body added itself to that of cutting his way through the snow. His
footing I could see often yielded, and he slid back, checking his
recession, however, by still plunging forward; thus, though the limbs
were incessantly exerted, it was, for a time, a mere motion of vibration
without any sensible translation. At the last stake the men shouted,
"_Nous avons finis!_" and I distinctly heard them through the falling
snow. By this time I was quite covered with the crystals which clung to
my wrapper. They also formed a heap upon my theodolite, rising over the
spirit-levels and embracing the lower portion of the vertical arc. The
work was done; I struck my theodolite and ascended to the hotel; the
greatest depth of snow through which I waded reaching, when I stood
erect, to within three inches of my breast.
[Sidenote: SWIFT DESCENT. 1859.]
The men returned; dinner was prepared and consumed; the disorder which
we had created made good; the rooms were swept, the mattresses replaced,
and the shutters fastened, where this was possible. We locked up the
house, and with light hearts and lithe limbs commenced the descent. My
aim now was to reach the source of the Arveiron, to examine the water
and inspect the vault. With this view we went straight down the
mountain. The inclinations were often extremely steep, and down these we
swept with an avalanche-velocity; indeed usually accompanied by an
avalanche of our own creation. On one occasion Balmat was for a moment
overwhelmed by the descending mass: the guides were startled, but he
emerged instantly. Tairraz followed him, and I followed Tairraz, all of
us rolling in the snow at the bottom of the slope as if it were so much
flour. My practice on the Finsteraarhorn rendered me at home here. One
of the porters could by no means be induced to try this flying mode of
descent. Simond carried my theodolite box, tied upon a crotchet on his
back; and once, while shooting down a slope, he incautiously allowed a
foot to get entangled; his momentum rolled him over and over down the
incline, the theodolite emerging periodically from the snow during his
successive revolutions. A succession of _glissades_ brought us with
amazing celerity to the bottom of the mountain, whence we picked our way
amid the covered boulders and over the concealed arms of the stream to
the source of the Arveiron.
The quantity of water issuing from the vault was considerable, and its
character that of true glacier water. It was turbid with suspended
matter, though not so turbid as in summer; but the difference in force
and quantity would, I think, be sufficient to account for the greater
summer turbidity. This character of the water could only be due to the
grinding motion of the glacier upon its bed; a motion which seems not to
be suspended even in the depth of winter. The temperature of the water
was the tenth of a degree Centigrade above zero; that of the ice was
half a degree below zero: this was also the temperature of the air,
while that of the snow, which in some places covered the ice-blocks, was
a degree and a quarter below zero.
[Sidenote: VAULT OF THE ARVEIRON. 1859.]
The entrance to the vault was formed by an arch of ice which had
detached itself from the general mass of the glacier behind: between
them was a space through which we could look to the sky above. Beyond
this the cave narrowed, and we found ourselves steeped in the blue light
of the ice. The roof of the inner arch was perforated at one place by a
shaft about a yard wide, which ran vertically to the surface of the
glacier. Water had run down the sides of this shaft, and, being
re-frozen below, formed a composite pillar of icicles at least twenty
feet high and a yard thick, stretching quite from roof to floor. They
were all united to a common surface at one side, but at the other they
formed a series of flutings of exceeding beauty. This group of columns
was bent at its base as if it had yielded to the forward motion of the
glacier, or to the weight of the arch overhead. Passing over a number of
large ice-blocks which partially filled the interior of the vault, we
reached its extremity, and here found a sloping passage with a perfect
arch of crystal overhead, and leading by a steep gradient to the air
above. This singular gallery was about seventy feet long, and was
floored with snow. We crept up it, and from the summit descended by a
glissade to the frontal portion of the cavern. To me this crystal cave,
with the blue light glistening from its walls, presented an aspect of
magical beauty. My delight, however, was tame compared with that of my
companions.
[Sidenote: MAJESTIC SCENE. 1859.]
Looking from the blue arch westwards, the heavens were seen filled by
crimson clouds, with fiery outliers reaching up to the zenith. On
quitting the vault I turned to have a last look at those noble sentinels
of the Mer de Glace, the Aiguille du Dru, and the Aiguille Verte. The
glacier below the mountains was in shadow, and its frozen precipices of
a deep cold blue. From this, as from a basis, the mountain cones sprang
steeply heavenward, meeting half way down the fiery light of the sinking
sun. The right-hand slopes and edges of both pyramids burned in this
light, while detached protuberant masses also caught the blaze, and
mottled the mountains with effulgent spaces. A range of minor peaks ran
slanting downwards from the summit of the Aiguille Verte; some of these
were covered with snow, and shone as if illuminated with the deep
crimson of a strontian flame. I was absolutely struck dumb by the
extraordinary majesty of this scene, and watched it silently till the
red light faded from the highest summits. Thus ended my winter
expedition to the Mer de Glace.
Next morning, starting at three o'clock, I was driven by my two guides
in an open sledge to Sallenches. The rain was pitiless and the road
abominable. The distance, I believe, is only six leagues, but it took us
five hours to accomplish it. The leading mule was beyond the reach of
Simond's whip, and proved a mere obstructive; during part of the way it
was unloosed, tied to the sledge, and dragged after it. Simond
afterwards mounted the hindmost beast and brought his whip to bear upon
the leader, the jerking he endured for an hour and a half seemed almost
sufficient to dislocate his bones. We reached Sallenches half an hour
late, but the diligence was behind its time by this exact interval. We
met it on the Pont St. Martin, and I transferred myself from the sledge
to the interior. This was the morning of the 30th of December, and on
the evening of the 1st of January I was in London.
[Sidenote: MY ASSISTANTS. 1859.]
I cannot finish this recital without saying one word about my men. Their
behaviour was admirable throughout. The labour was enormous, but it was
manfully and cheerfully done. I know Simond well; he is intelligent,
truthful, and affectionate, and there is no guide of my acquaintance for
whom I have a stronger regard. Joseph Tairraz is an extremely
intelligent and able guide, and on this trying occasion proved himself
worthy of my highest praise and commendation. Their two companions upon
the glacier, Edouard Balmat (le Petit Balmat) and Joseph Simond (fils
d'Auguste), acquitted themselves admirably; and it also gives me
pleasure to bear testimony to the willing and efficient service of
François Ravanal, who attended upon me during the observations.
FOOTNOTES:
[A] Emerson.
PART II.
CHIEFLY SCIENTIFIC.
Aber im stillen Gemach entwirft bedeutende Zirkel
Sinnend der Weise, beschleicht forschend den schaffenden Geist,
Prüft der Stoffe Gewalt, der Magnete Hassen und Lieben,
Folgt durch die Lüfte dem Klang, folgt durch den Aether dem Strahl,
Sucht das vertraute Gesetz in des Zufalls grausenden Wundern,
Sucht den ruhenden Pol in der Erscheinungen Flucht.
Schiller.
ON LIGHT AND HEAT.
(1.)
[Sidenote: THEORIES OF LIGHT.]
What is Light? The ancients supposed it to be something emitted by the
eyes, and for ages no notion was entertained that it required time to
pass through space. In the year 1676 Römer first proved that the light
from Jupiter's satellites required a certain time to cross the earth's
orbit. Bradley afterwards found that, owing to the velocity with which
the earth flies through space, the rays of the stars are slightly
inclined, just as rain-drops which descend vertically appear to meet us
when we move swiftly through the shower. In Kew Gardens there is a
sun-dial commemorative of this discovery, which is called the
_aberration of light_. Knowing the velocity of the earth, and the
inclination of the stellar rays, Bradley was able to calculate the
velocity of light; and his result agrees closely with that of Römer.
Celestial distances were here involved, but a few years ago M. Fizeau,
by an extremely ingenious contrivance, determined the time required by
light to pass over a distance of about 9000 yards; and his experiment is
quite in accordance with the results of his predecessors.
But what is it which thus moves? Some, and among the number Newton,
imagined light to consist of particles darted out from luminous bodies.
This is the so-called Emission-Theory, which was held by some of the
greatest men: Laplace, for example, accepted it; and M. Biot has
developed it with a lucidity and power peculiar to himself. It was first
opposed by the astronomer Huyghens, and afterwards by Euler, both of
whom supposed light to be a kind of undulatory motion; but they were
borne down by their great antagonists, and the emission-theory held its
ground until the commencement of the present century, when Thomas Young,
Professor of Natural Philosophy in the Royal Institution, reversed the
scientific creed by placing the Theory of Undulation on firm
foundations. He was followed by a young Frenchman of extraordinary
genius, who, by the force of his logic and the conclusiveness of his
experiments, left the Wave-Theory without a competitor. The name of this
young Frenchman was Augustin Fresnel.
Since his time some of the ablest minds in Europe have been applied to
the investigation of this subject; and thus a mastery, almost
miraculous, has been attained over the grandest and most subtle of
natural phenomena. True knowledge is always fruitful, and a clear
conception regarding any one natural agent leads infallibly to better
notions regarding others. Thus it is that our knowledge of light has
corrected and expanded our knowledge of _heat_, while the latter, in its
turn, will assuredly lead us to clearer conceptions regarding the other
forces of Nature.
I think it will not be a useless labour if I here endeavour to state, in
a simple manner, our present views of light and heat. Such knowledge is
essential to the explanation of many of the phenomena referred to in the
foregoing pages; and even to the full comprehension of the origin of the
glaciers themselves. A few remarks on the nature of sound will form a
fit introduction.
[Sidenote: NATURE OF SOUND.]
It is known that sound is conveyed to our organs of hearing by the air:
a bell struck in a vacuum emits no sound, and even when the air is thin
the sound is enfeebled. Hawksbee proved this by the air-pump; De
Saussure fired a pistol at the top of Mont Blanc,--I have repeated the
experiment myself, and found, with him, that the sound is feebler than
at the sea level. Sound is not produced by anything projected through
the air. The explosion of a gun, for example, is sent forward by a
motion of a totally different kind from that which animates the bullet
projected from the gun: the latter is a motion of _translation_; the
former, one of _vibration_. To use a rough comparison, sound is
projected through the air as a push is through a crowd; it is the
propagation of a _wave_ or _pulse_, each particle taking up the motion
of its neighbour, and delivering it on to the next. These aërial waves
enter the external ear, meet a membrane, the so-called tympanic
membrane, which is drawn across the passage at a certain place, and
break upon it as sea-waves do upon the shore. The membrane is shaken,
its tremors are communicated to the auditory nerve, and transmitted by
it to the brain, where they produce the impression to which we give the
name of sound.
[Sidenote: CAUSE OF MUSIC.]
In the tumult of a city, pulses of different kinds strike irregularly
upon the tympanum, and we call the effect _noise_; but when a succession
of impulses reach the ear _at regular intervals_ we feel the effect as
_music_. Thus, a vibrating string imparts a series of shocks to the air
around it, which are transmitted with perfect regularity to the ear, and
produce a _musical note_. When we hear the song of a soaring lark we may
be sure that the entire atmosphere between us and the bird is filled
with pulses, or undulations, or waves, as they are often called,
produced by the little songster's organ of voice. This organ is a
vibrating instrument, resembling, in principle, the reed of a clarionet.
Let us suppose that we hear the song of a lark, elevated to a height of
500 feet in the air. Before this is possible, the bird must have
agitated a sphere of air 1000 feet in diameter; that is to say, it must
have communicated to 17,888 tons of air a motion sufficiently intense to
be appreciated by our organs of hearing.
[Sidenote: CAUSE OF PITCH.]
Musical sounds differ in _pitch_: some notes are high and shrill, others
low and deep. Boys are chosen as choristers to produce the shrill
notes; men are chosen to produce the bass notes. Now, the sole
difference here is, that the boy's organ vibrates _more rapidly_ than
the man's--it sends a greater number of impulses per second to the ear.
In like manner, a short string emits a higher note than a long one,
because it vibrates more quickly. The greater the number of vibrations
which any instrument performs in a given time, the higher will be the
pitch of the note produced. The reason why the hum of a gnat is shriller
than that of a beetle is that the wings of the small insect vibrate more
quickly than those of the larger one. We can, with suitable
arrangements, make those sonorous vibrations visible to the eye;[A] and
we also possess instruments which enable us to tell, with the utmost
exactitude, the number of vibrations due to any particular note. By such
instruments we learn that a gnat can execute many thousand flaps of its
little wings in a second of time.
[Sidenote: NATURE OF LIGHT.]
In the study of nature the coarser phenomena, which come under the
cognizance of the senses, often suggest to us the finer phenomena which
come under the cognizance of the mind; and thus the vibrations which
produce sound, and which, as has been stated, can be rendered visible to
the eye by proper means, first suggested that _light_ might be due to a
somewhat similar action. This is now the universal belief. A luminous
body is supposed to have its atoms, or molecules, in a state of intense
vibration. The motions of the atoms are supposed to be communicated to
a medium suited to their transmission, as air is to the transmission of
sound. This medium is called the _luminiferous ether_, and the little
billows excited in it speed through it with amazing celerity, enter the
pupil of the eye, pass through the humours, and break upon the retina or
optic nerve, which is spread out at the back of the eye. Hence the
tremors they produce are transmitted along the nerve to the brain, where
they announce themselves as _light_. The swiftness with which the waves
of light are propagated through the ether, is however enormously greater
than that with which the waves of sound pass through the air. An aërial
wave of sound travels at about the rate of 1100 feet in a second: a wave
of light leaves 192,000 miles behind it in the same time.
[Sidenote: CAUSE OF COLOUR.]
Thus, then, in the case of sound, we have the sonorous body, the air,
and the auditory nerve, concerned in the phenomenon; in the case of
light, we have the luminous body, the ether, and the optic nerve. The
fundamental analogy of sound and light is thus before us, and it is
easily remembered. But we must push the analogy further. We know that
the white light which comes to us from the sun is made up of an infinite
number of coloured rays. By refraction with a prism we can separate
those rays from each other, and arrange them in the series of colours
which constitute the solar spectrum. The rainbow is an imperfect or
_impure_ spectrum, produced by the drops of falling rain, but by prisms
we can unravel the white light into pure red, orange, yellow, green,
blue, indigo, and violet. Now, this spectrum is to the eye what the
gamut is to the ear; each colour represents a note, and _the different
colours represent notes of different pitch_. The vibrations which
produce the impression of red are _slower_, and the waves which they
produce are _longer_, than those to which we owe the sensation of
violet; while the vibrations which excite the other colours are
intermediate between these two extremes. This, then, is the second grand
analogy between light and sound: _Colour answers to Pitch_. There is
therefore truth in the figure when we say that the gentian of the Alps
sings a shriller note than the wild rhododendron, and that the red glow
of the mountains at sunset is of a lower pitch than the blue of the
firmament at noon.
[Sidenote: LENGTH OF ETHEREAL WAVES.]
These are not fanciful analogies. To the mind of the philosopher these
waves of ether are almost as palpable and certain as the waves of the
sea, or the ripples on the surface of a lake. The length of the waves,
both of sound and light, and the number of shocks which they
respectively impart to the ear and eye, have been the subjects of the
strictest measurement. Let us here go through a simple calculation. It
has been found that 39,000 waves of red light placed end to end would
make up an inch. How many inches are there in 192,000 miles? My youngest
reader can make the calculation for himself, and find the answer to be
12,165,120,000 inches. It is evident that, if we multiply this number by
39,000, we shall obtain the number of waves of red light in 192,000
miles; this number is 474,439,680,000,000. _All these waves enter the
eye in one second_; thus the expression "I see red colour," strictly
means, "My eye is now in receipt of four hundred and seventy-four
millions of millions of impulses per second." To produce the impression
of violet light a still greater number of impulses is necessary; the
wave-length of violet is the 1/57500th part of an inch, and the number
of shocks imparted in a second by waves of this length is, in round
numbers, six hundred and ninety-nine millions of millions. The other
colours of the spectrum, as already stated, rise gradually in pitch from
the red to the violet.
A very curious analogy between the eye and ear may here be noticed. The
range of seeing is different in different persons--some see a longer
spectrum than others; that is to say, rays which are obscure to some are
luminous to others. Dr. Wollaston pointed out a similar fact as regards
hearing; the range of which differs in different individuals. Savart has
shown that a good ear can hear a musical note produced by 8 shocks in a
second; it can also hear a note produced by 24,000 shocks in a second;
but there are ears in which the range is much more limited. It is
possible indeed to produce a sound which shall be painfully shrill to
one person, while it is quite unheard by another. I once crossed a Swiss
mountain in company with a friend; a donkey was in advance of us, and
the dull tramp of the animal was plainly heard by my companion; but to
me this sound was almost masked by the shrill chirruping of innumerable
insects which thronged the adjacent grass; my friend heard nothing of
this, it lay quite beyond his range of hearing.
A third and most important analogy between sound and light is now to be
noted; and it will be best understood by reference to something more
tangible than either. When a stone is thrown into calm water a series of
rings spread themselves around the centre of disturbance. If a second
stone be thrown in at some distance from the first, the rings emanating
from both centres will cross each other, and at those points where the
ridge of one wave coincides with the ridge of another the water will be
lifted to a greater height. At those points, on the contrary, where the
ridge of one wave crosses the furrow of another, we have both
obliterated, and the water restored to its ordinary level. Where two
ridges or two furrows unite, we have a case of _coincidence_; but where
a ridge and a furrow unite we have what is called _interference_. It is
quite possible to send two systems of waves into the same channel, and
to hold back one system a little, so that its ridges shall coincide
with the furrows of the other system. The "interference" would be here
complete, and the waves thus circumstanced would mutually destroy each
other, smooth water being the result. In this way, by the addition of
motion to motion, _rest_ may be produced.
[Sidenote: LIGHT ADDED TO LIGHT MAKES DARKNESS.]
In a precisely similar manner two systems of sonorous waves can be
caused to interfere and mutually to destroy each other: thus, by adding
sound to sound, _silence_ may be produced. Two beams of light also may
be caused to interfere and effect their mutual extinction: thus, by
adding light to light, we can produce _darkness_. Here indeed we have a
critical analogy between sound and light--_the_ one, in fact, which
compels the most profound thinkers of the present day to assume that
light, like sound, is a case of undulatory motion.
We see here the vision of the intellect prolonged beyond the boundaries
of sense into the region of what might be considered mere imagination.
But, unlike other imaginations, we can bring ours to the test of
experiment; indeed, so great a mastery have we obtained over these
waves, which eye has not seen, nor ear heard, that we can with
mathematical certainty cause them to coincide or to interfere, to help
each other or to destroy each other, at pleasure. It is perhaps possible
to be a little more precise here. Let two stones--with a small distance
between them--be dropped into water at the same moment; a system of
circular waves will be formed round each stone. Let the distance from
one little crest to the next following one be called _the length of the
wave_, and now let us inquire what will take place at a point equally
distant from the places where the two stones were dropped in. Fixing our
attention upon the ridge of the first wave in each case, it is manifest
that, as the water propagates both systems with the same velocity, the
two foremost ridges will reach the point in question at the same
moment; the ridge of one would therefore coincide with the ridge of the
other, and the water at this point would be lifted to a height greater
than that of either of the previous ridges.
[Sidenote: COINCIDENCE AND INTERFERENCE.]
Again, supposing that by any means we had it in our power to retard one
system of waves so as to cause the first ridge of the one to be exactly
one wave length behind the first ridge of the other, when they arrive at
the point referred to. It is plain that the first ridge of the retarded
system now falls in with the second ridge of the unretarded system, and
we have another case of coincidence. A little reflection will show the
same to be true when one system is retarded any number of _whole
wave-lengths_; the first ridge of the retarded system will always, at
the point referred to, coincide with a _ridge_ of the unretarded system.
But now suppose the one system to be retarded only _half a wave-length_;
it is perfectly clear that, in this case the first ridge of the retarded
system would fall in with the first _furrow_ of the unretarded system,
and instead of coincidence we should have interference. One system, in
fact, would tend to make a hollow at the point referred to, the other
would tend to make a hill, and thus the two systems would oppose and
neutralize each other, so that neither the hollow nor the hill would be
produced; the water would maintain its ordinary level. What is here said
of a single half-wave-length of retardation, is also true if the
retardation amount to any _odd_ number of half-wave-lengths. In all such
cases we should have the ridge of the one system falling in with the
furrow of the other; a mutual destruction of the waves of both systems
being the consequence. The same remarks apply when the point, instead of
being equally distant from both stones, is an even or an odd number of
semi-undulations farther from the one than from the other. In the former
case we should have coincidence, and in the latter case interference,
at the point in question.
[Sidenote: LIQUID WAVES.]
To the eye of a person who understands these things, nothing can be more
interesting than the rippling of water under certain circumstances. By
the action of interference its surface is sometimes shivered into the
most beautiful mosaic, shifting and trembling as if with a kind of
visible music. When the tide advances over a sea-beach on a calm and
sunny day, and its tiny ripples enter, at various points, the clear
shallow pools which the preceding tide had left behind, the little
wavelets run and climb and cross each other, and thus form a lovely
_chasing_, which has its counterpart in the lines of light converged by
the ripples upon the sand underneath. When waves are skilfully generated
in a vessel of mercury, and a strong light reflected from the surface of
the metal is received upon a screen, the most beautiful effects may be
observed. The shape of the vessel determines, in part, the character of
the figures produced; in a circular dish of mercury, for example, a
disturbance at the centre propagates itself in circular waves, which
after reflection again encircle the centre. If the point of disturbance
be a little removed from the centre, the intersections of the direct and
reflected waves produce the magnificent chasing shown in the annexed
figure (16), which I have borrowed from the excellent work on Waves by
the Messrs. Weber. The luminous figure reflected from such a surface is
exceedingly beautiful. When the mercury is lightly struck by a glass
point, in a direction concentric with the circumference of the vessel,
the lines of light run round the vessel in mazy coils, interlacing and
unravelling themselves in the most wonderful manner. If the vessel be
square, a splendid mosaic is produced by the crossing of the direct and
reflected waves. Description, however, can give but a feeble idea of
these exquisite effects;--
"Thou canst not wave thy staff in the air,
Or dip thy paddle in the lake,
But it carves the brow of beauty there,
And the ripples in rhymes the oar forsake."
[Sidenote: CHASING PRODUCED BY WAVES.]
[Illustration: Fig. 16. Chasing produced by waves.]
[Sidenote: EFFECT OF RETARDATION.]
Now, all that we have said regarding the retardation of the waves of
water, by a whole undulation and a semi-undulation, is perfectly
applicable to the case of light. Two luminous points may be placed near
to each other so as to resemble the two stones dropped into the water;
and when the light of these is properly received upon a screen, or
directly upon the retina, we find that at some places the action of the
rays upon each other produces darkness, and at others augmented light.
The former places are those where the rays emitted from one point are an
_odd_ number of semi-undulations in advance of the rays sent from the
other; the latter places are those where the difference of path
described by the rays is either nothing, or an _even_ number of
semi-undulations. Supposing _a_ and _b_ (Fig. 17) to be two such
sources of light, and S R a screen on which the light falls; at a point
_l_, equally distant from _a_ and _b_, we have _light_; at a point _d_,
where _a d_ is half an undulation longer than _b d_, we have darkness;
at _l'_, where _a l'_ is a whole wave-length, or two semi-undulations,
longer than _b l'_, we again have light; and at a point _d'_, where the
difference is three semi-undulations, we have darkness; and thus we
obtain a series of bright and dark spaces as we recede laterally from
the central point _l_.
[Illustration: Fig. 17. Diagram explanatory of Interference.]
Let a bit of tin foil be closely pasted upon a piece of glass, and the
edge of a penknife drawn across the foil so as to produce a slit.
Looking through this slit at a small and distant light, we find the
light spread out in a direction at right angles to the slit, and if the
light looked at be _monochromatic_, that is, composed of a single
colour, we shall have a series of bright and dark bars corresponding to
the points at which the rays from the different points of the slit
alternately coincide and interfere upon the retina. By properly
drawing a knife across a sheet of letter-paper a suitable slit may also
be obtained; and those practised in such things can obtain the effect by
looking through their fingers or their eyelashes.
[Illustration: INTERFERENCE SPECTRA, PRODUCED BY DIFFRACTION.
Fig. 18. _To face_ p. 235.]
[Sidenote: CHROMATIC EFFECTS.]
But if the light looked at be white, the light of a candle for example,
or of a jet of gas, instead of having a series of bright and dark bars,
we have the bars _coloured_. And see how beautifully this harmonizes
with what has been already said regarding the different lengths of the
waves which produce different colours. Looking again at Fig. 17 we see
that a certain obliquity is necessary to cause one ray to be a whole
undulation in advance of the other at the point _l'_; but it is
perfectly manifest that the obliquity must depend upon the length of the
undulation; a long undulation would require a greater obliquity than a
short one; red light, for example, requires a greater obliquity than
blue light; so that if the point _l'_ represents the place where the
first bar of red light would be at its maximum strength, the maximum for
blue would lie a little to the left of _l'_; the different colours are
in this way separated from each other, and exhibit themselves as
distinct fringes when a distant source of white light is regarded
through a narrow slit.
By varying the shape of the aperture we alter the form of the chromatic
image. A circular aperture, for example, placed in front of a telescope
through which a point of white light is regarded, is seen surrounded by
a concentric system of coloured rings. If we multiply our slits or
apertures the phenomena augment in complexity and splendour. To give
some notion of this I have copied from the excellent work of M. Schwerd
the annexed figure (Fig. 18) which represents the gorgeous effect
observed when a distant point of light is looked at through two gratings
with slits of different widths.[B] A bird's feather represents a
peculiar system of slits, and the effect observed on properly looking
through it is extremely interesting.
[Sidenote: COLOURS OF THIN FILMS.]
There are many ways by which the retardation necessary to the production
of interference is effected. The splendid colours of a soap-bubble are
entirely due to interference; the beam falling upon the transparent film
is partially reflected at its outer surface, but a portion of it enters
the film and is reflected at its _inner_ surface. The latter portion
having crossed the film and returned, is retarded, in comparison with
the former, and, if the film be of suitable thickness, these two beams
will clash and extinguish each other, while another thickness will cause
the beams to coincide and illuminate the film with a light of greater
intensity. From what has been said it must be manifest that to make two
red beams thus coincide a thicker film would be required than would be
necessary for two blue or green beams; thus, when the thickness of the
bubble is suitable for the development of red, it is not suitable for
the development of green, blue, &c.; the consequence is that we have
different colours at different parts of the bubble. Owing to its
compactness and to its being shaded by a covering of débris from the
direct heat of the sun, the ice underneath the moraines of glaciers
appears sometimes of a pitchy blackness. While cutting such ice with my
axe I have often been surprised and delighted by sudden flashes of
coloured light which broke like fire from the mass. These flashes were
due to internal rupture, by which fissures were produced as thin as the
film of a soap-bubble; the colours being due to the interference of the
light reflected from the opposite sides of the fissures.
If spirit of turpentine, or olive oil, be thrown upon water, it speedily
spreads in a thin film over the surface, and the most gorgeous
chromatic phenomena may be thus produced. Oil of lemons is also
peculiarly suited to this experiment. If water be placed in a tea-tray,
and light of sufficient intensity be suffered to fall upon it, this
light will be reflected from the upper and under surfaces of the film of
oil, and the colours thus produced may be received upon a screen, and
seen at once by many hundred persons. If the oil of cinnamon be used,
fine colours are also obtained, and the breaking up of this film
exhibits a most interesting case of molecular action. By using a kind of
varnish, instead of oil, Mr. Delarue has imparted such tenacity to these
films that they may be removed from the water on which they rest and
preserved for any length of time. By such films the colours of certain
beetles, and of the wings of certain insects, may be accurately
imitated; and a rook's feather may be made to shine with magnificent
iridescences. The colours of tempered metals, and the beautiful
metallochrome of Nobili are also due to a similar cause.
[Sidenote: DIFFRACTION.]
These colours are called the colours of _thin plates_, and are
distinguished in treatises on optics from the coloured bars and fringes
above referred to, which are produced by _diffraction_, or the bending
of the waves round the edge of an object. One result of this bending,
which is of interest to us, was obtained by the celebrated Thomas Young.
Permitting a beam of sunlight to enter a dark room through an aperture
made with a fine needle, and placing in the path of the beam a bit of
card one-thirtieth of an inch wide, he found the shadow of this card, or
rather the line on which its shadow might be supposed to fall, always
_bright_; and he proved the effect to be due to the bending of the waves
of ether round the two edges of the card, and their coincidence at the
other side. It has, indeed, been shown by M. Poisson, that the centre of
the shadow of a small circular opaque disk which stands in the way of a
beam diverging from a point is exactly as much illuminated as if the
disk were absent. The singular effects described by M. Necker in the
letter quoted at page 178 at once suggest themselves here; and we see
how possible it is for the solar rays, in grazing a distant tree, so to
bend round it as to produce upon the retina, where shadow might be
expected, the impression of a tree of light.[C] Another effect of
diffraction is especially interesting to us at present. Let the seed of
lycopodium be scattered over a glass plate, or even like a cloud in the
air, and let a distant point of light be regarded through it; the
luminous point will appear surrounded by a series of coloured rings, and
when the light is intense, like the electric or the Drummond light, the
effect is exceedingly fine.
[Sidenote: CLOUD IRIDESCENCE, ETC., EXPLAINED.]
And now for the application of these experiments. I have already
mentioned a series of coloured rings observed around the sun by Mr.
Huxley and myself from the Rhone glacier; I have also referred to the
cloud iridescences on the Aletschhorn; and to the colours observed
during my second ascent of Monte Rosa, the magnificence of which is
neither to be rendered by pigments nor described in words. All these
splendid phenomena are, I believe, produced by diffraction, the vesicles
or spherules of water in the case of the cloud acting the part of the
sporules in the case of the lycopodium. The coloured fringe which
surrounds the _Spirit of the Brocken_, and the spectra which I have
spoken of as surrounding the sun, are also produced by diffraction. By
the interference of their rays in the earth's atmosphere the stars can
momentarily quench themselves; and probably to an intermittent action of
this kind their twinkling, and the swift chromatic changes already
mentioned, are due. Does not all this sound more like a fairy tale than
the sober conclusions of science? What effort of the imagination could
transcend the realities here presented to us? The ancients had their
spheral melodies, but have not we ours, which only want a sense
sufficiently refined to hear them? Immensity is filled with this music;
wherever a star sheds its light its notes are heard. Our sun, for
example, thrills concentric waves through space, and every luminous
point that gems our skies is surrounded by a similar system. I have
spoken of the rising, climbing and crossing of the tiny ripples of a
calm tide upon a smooth strand; but what are they to those intersecting
ripples of the "uncontinented deep" by which Infinity is engine-turned!
Crossing solar and stellar distances, they bring us the light of sun and
stars; thrilled back from our atmosphere, they give us the blue radiance
of the sky; rounding liquid spherules, they clash at the other side, and
the survivors of the tumult bear to our vision the wondrous cloud-dyes
of Monte Rosa.
FOOTNOTES:
[A] The vibrations of the air of a room in which a musical instrument is
sounded may be made manifest by the way in which fine sand arranges
itself upon a thin stretched membrane over which it is strewn; and
indeed Savart has thus rendered visible the vibrations of the tympanum
itself. Every trace of sand was swept from a paper drum held in the
clock-tower of Westminster when the Great Bell was sounded. Another way
of showing the propagation of aërial pulses is to insert a small gas jet
into a vertical glass tube about a foot in length, in which the flame
may be caused to burn tranquilly. On pitching the voice to the note of
an open tube a foot long, the little flame quivers, stretches itself,
and responds by producing a clear melodious note of the same pitch as
that which excited it. The flame will continue its song for hours
without intermission.
[B] I am not aware whether in his own country, or in any other, a
recognition at all commensurate with the value of the performance has
followed Schwerd's admirable essay entitled 'The Phenomena of
Diffraction deduced from the Theory of Undulation.'
[C] I think, however, that the strong irradiation from the glistening
sides of the twigs and branches must also contribute to the result.
[Sidenote: RADIANT HEAT.]
(2.)
Thus, then, we have been led from Sound to Light, and light now in its
turn will lead us to _Radiant Heat_; for in the order in which they are
here mentioned the conviction arose that they are all three different
kinds of motion. It has been said that the beams of the sun consist of
rays of different colours, but this is not a complete statement of the
case. The sun emits a multitude of rays which are perfectly
non-luminous; and the same is true, in a still greater degree, of our
artificial sources of illumination. Measured by the quantity of heat
which they produce, 90 per cent. of the rays emanating from a flame of
oil are obscure; while 99 out of every 100 of those which emanate from
an alcohol flame are of the same description.[A]
[Sidenote: OBSCURE RAYS.]
In fact, the visible solar spectrum simply embraces an interval of rays
of which the eye is formed to take cognizance, but it by no means marks
the limits of solar action. Beyond the violet end of the spectrum we
have obscure rays capable of producing chemical changes, and beyond the
red we have rays possessing a high heating power, but incapable of
exciting the impression of light. This latter fact was first established
by Sir William Herschel, and it has been amply corroborated since.
The belief now universally prevalent is, that the rays of heat differ
from the rays of light simply as one colour differs from another. As the
waves which produce red are longer than those which produce yellow, so
the waves which produce this obscure heat are longer than those which
produce red. In fact, it may be shown that the longest waves never reach
the retina at all; they are completely absorbed by the humours of the
eye.
What is true of the sun's obscure rays is also true of calorific rays
emanating from any obscure source,--from our own bodies, for example, or
from the surface of a vessel containing boiling water. We must, in fact,
figure a warm body also as having its particles in a state of vibration.
When these motions are communicated from particle to particle of the
body the heat is said to be _conducted_; when, on the contrary, the
particles transmit their vibrations through the surrounding ether, the
heat is said to be _radiant_. This radiant heat, though obscure,
exhibits a deportment exactly similar to light. It may be refracted and
reflected, and collected in the focus of a mirror or of a suitable lens.
The principle of interference also applies to it, so that by adding heat
to heat we can produce _cold_. The identity indeed is complete
throughout, and, recurring to the analogy of sound, we might define
this radiant heat to be light of too low a pitch to be visible.
I have thus far spoken of _obscure_ heat only; but the selfsame ray may
excite both light and heat. The red rays of the spectrum possess a very
high heating power. It was once supposed that the heat of the spectrum
was an essence totally distinct from its light; but a profounder
knowledge dispels this supposition, and leads us to infer that the
selfsame ray, falling upon the nerves of feeling, excites heat, and
falling upon the nerves of seeing, excites light. As the same electric
current, if sent round a magnetic needle, along a wire, and across a
conducting liquid, produces different physical effects, so also the same
agent acting upon different organs of the body affects our consciousness
differently.
FOOTNOTES:
[A] Melloni.
(3.)
[Sidenote: HEAT A KIND OF MOTION.]
Heat has been defined in the foregoing section as a motion of the
molecules or atoms of a body; but though the evidence in favour of this
view is at present overwhelming, I do not ask the reader to accept it as
a certainty, if he feels sceptically disposed. In this case, I would
only ask him to accept it as a symbol. Regarded as a mere physical
image, a kind of paper-currency of the mind, convertible, in due time,
into the gold of truth, the hypothesis will be found exceedingly useful.
All known bodies possess more or less of this molecular motion, and all
bodies are communicating it to the ether in which they are immersed. Ice
possesses it. Ice before it melts attains a temperature of 32° Fahr.,
but the substance in winter often possesses a temperature far below 32°,
so that in rising to 32° it is _warmed_. In experimenting with ice I
have often had occasion to cool it to 100° and more below the freezing
point, and to warm it afterwards up to 32°.
If then we stand before a wall of ice, the wall radiates heat to us, and
we also radiate heat to it; but the quantity which we radiate being
greater than that which the ice radiates, we lose more than we gain, and
are consequently chilled. If, on the contrary, we stand before a warm
stove, a system of exchanges also takes place; but here the quantity we
receive is in excess of the quantity lost, and we are warmed by the
difference.
In like manner the earth radiates heat by day and by night into space,
and against the sun, moon, and stars. By day, however, the quantity
received is greater than the quantity lost, and the earth is warmed; by
night the conditions are reversed; the earth radiates more heat than is
sent to her by the moon and stars, and she is consequently cooled.
But here an important point is to be noted:--the earth receives the heat
of the sun, moon, and stars, in great part as _luminous_ heat, but she
gives it out as _obscure_ heat. I do not now speak of the heat reflected
by the earth into space, as the light of the moon is to us; but of the
heat which, after it has been absorbed by the earth, and has contributed
to warm it, is radiated into space, as if the earth itself were its
independent source. Thus we may properly say that the heat radiated from
the earth is _different in quality_ from that which the earth has
received from the sun.
[Sidenote: QUALITIES OF HEAT.]
In one particular especially does this difference of quality show
itself; besides being non-luminous, the heat radiated from the earth is
more easily intercepted and absorbed by almost all transparent
substances. A vast portion of the sun's rays, for example, can pass
instantaneously through a thick sheet of water; gunpowder could easily
be fired by the heat of the sun's rays converged by passing through a
thick water lens; the drops upon leaves in greenhouses often act as
lenses, and cause the sun to burn the leaves upon which they rest. But
with regard to the rays of heat emanating from an obscure source, they
are all absorbed by a layer of water less than the 20th of an inch in
thickness: water is opaque to such rays, and cuts them off almost as
effectually as a metallic screen. The same is true of other liquids, and
also of many transparent solids.
[Sidenote: THE ATMOSPHERE LIKE A RATCHET.]
Assuming the same to be true of gaseous bodies, that they also intercept
the obscure rays much more readily than the luminous ones, it would
follow that while the sun's rays penetrate our atmosphere with freedom,
the change which they undergo in warming the earth deprives them in a
measure of this penetrating power. They can reach the earth, but _they
cannot get back_; thus the atmosphere acts the part of a ratchet-wheel
in mechanics; it allows of motion in one direction, but prevents it in
the other.
De Saussure, Fourier, M. Pouillet, and Mr. Hopkins have developed this
speculation, and drawn from it consequences of the utmost importance;
but it nevertheless rested upon a basis of conjecture. Indeed some of
the eminent men above-named deemed its truth beyond the possibility of
experimental verification. Melloni showed that for a distance of 18 or
20 feet the absorption of obscure rays by the atmosphere was absolutely
inappreciable. Hence, the _total_ absorption being so small as to elude
even Melloni's delicate tests, it was reasonable to infer that
_differences_ of absorption, if such existed at all, must be far beyond
the reach of the finest means which we could apply to detect them.
[Sidenote: DIFFERENCES OF ABSORPTION BY GASES.]
This exclusion of one of the three states of material aggregation from
the region of experiment was, however, by no means satisfactory; for our
right to infer, from the deportment of a solid or a liquid towards
radiant heat, the deportment of a gas, is by no means evident. In both
liquids and solids we have the molecules closely packed, and more or
less chained by the force of cohesion; in gases, on the contrary, they
are perfectly free, and widely separated. How do we know that the
interception of radiant heat by liquids and solids may not be due to an
arrangement and comparative rigidity of their parts, which gases do not
at all share? The assumption which took no note of such a possibility
seemed very insecure, and called for verification.
My interest in this question was augmented by the fact, that the
assumption referred to lies, as will be seen, at the root of the glacier
question. I therefore endeavoured to fill the gap, and to do for gases
and vapours what had been already so ably done for liquids and solids by
Melloni. I tried the methods heretofore pursued, and found them
unavailing; oxygen, hydrogen, nitrogen, and atmospheric air, examined by
such methods, showed no action upon radiant heat. Nature was dumb, but
the question occurred, "Had she been addressed in the proper language?"
If the experimentalist is convinced of this, he will rest content even
with a negative; but the absence of this conviction is always a source
of discomfort, and a stimulus to try again.
The principle of the method finally applied is all that can here be
referred to; and it, I hope, will be quite intelligible. Two beams of
heat, from two distinct sources, were allowed to fall upon the same
instrument,[A] and to contend there for mastery. When both beams were
perfectly equal, they completely neutralized each other's action; but
when one of them was in any sensible degree stronger than the other, the
predominance of the former was shown by the instrument. It was so
arranged that one of the conflicting beams passed through a tube which
could be exhausted of air, or filled with any gas; thus varying at
pleasure the medium through which it passed. The question then was,
supposing the two beams to be equal when the tube was filled with air,
will the exhausting of the tube disturb the equality? The answer was
affirmative; the instrument at once showed that a greater quantity of
heat passed through the vacuum than through the air.
The experiment was so arranged that the effect thus produced was very
large as measured by the indications of the instrument. But the action
of the simple gases, oxygen, hydrogen, and nitrogen, was incomparably
less than that produced by some of the compound gases, while these
latter again differed widely from each other. Vapours exhibited
differences of equal magnitude. The experiments indeed proved that
gaseous bodies varied among themselves, as to their power of
transmitting radiant heat, just as much as liquids and solids. It was in
the highest degree interesting to observe how a gas or vapour of perfect
transparency, as regards light, acted like an opaque screen upon the
heat. To the eye, the gas within the tube might be as invisible as the
air itself, while to the radiant heat it behaved like a cloud which it
was almost impossible to penetrate.
[Sidenote: SELECTED HEAT.]
Applying the same method, I have found that from the sun, from the
electric light, or from the lime-light, a large amount of heat can be
selected, which is unaffected not only by air, but by the most energetic
gases that experiment has revealed to me; while this same heat, when it
has its _quality_ changed by being rendered obscure, is powerfully
intercepted. Thus the bold and beautiful speculation above referred to
has been made an experimental fact; the radiant heat of the sun does
certainly pass through the atmosphere to the earth with greater
facility than the radiant heat of the earth can escape into space.
[Sidenote: POSSIBLE HEAT OF NEPTUNE.]
It is probable that, were the earth unfurnished with this atmospheric
swathing, its conditions of temperature would be such as to render it
uninhabitable by man; and it is also probable that a suitable atmosphere
enveloping the most distant planet might render it, as regards
temperature, perfectly habitable. If the planet Neptune, for example, be
surrounded by an atmosphere which permits the solar and stellar rays to
pass towards the planet, but cuts off the escape of the warmth which
they excite, it is easy to see that such an accumulation of heat may at
length take place as to render the planet a comfortable habitation for
beings constituted like ourselves.[B]
But let us not wander too far from our own concerns. Where radiant heat
is allowed to fall upon an absorbing substance, a certain thickness of
the latter is always necessary for the absorption. Supposing we place a
thin film of glass before a source of heat, a certain percentage of the
heat will pass through the glass, and the remainder will be absorbed.
Let the transmitted portion fall upon a second film similar to the
first, a smaller percentage than before will be absorbed. A third plate
would absorb still less, a fourth still less; and, after having passed
through a sufficient number of layers, the heat would be so _sifted_
that all the rays capable of being absorbed by glass would be abstracted
from it. Suppose all these films to be placed together so as to form a
single thick plate of glass, it is evident that the plate must act upon
the heat which falls upon it, in such a manner that the major portion is
absorbed _near the surface at which the heat enters_. This has been
completely verified by experiment.
[Sidenote: COLD OF UPPER ATMOSPHERE.]
Applying this to the heat radiated from the earth, it is manifest that
the greatest quantity of this heat will be absorbed by the lowest
atmospheric strata. And here we find ourselves brought, by
considerations apparently remote, face to face with the fact upon which
the existence of all glaciers depends, namely, the comparative coldness
of the upper regions of the atmosphere. The sun's rays can pass in a
great measure through these regions without heating them; and the
earth's rays, which they might absorb, hardly reach them at all, but are
intercepted by the lower portions of the atmosphere.[C]
Another cause of the greater coldness of the higher atmosphere is the
expansion of the denser air of the lower strata when it ascends. The
dense air makes room for itself by pushing back the lighter and less
elastic air which surrounds it: _it does work_, and, to perform this
work, a certain amount of heat must be consumed. It is the consumption
of this heat--its absolute annihilation as heat--that chills the
expanded air, and to this action a share of the coldness of the higher
atmosphere must undoubtedly be ascribed. A third cause of the difference
of temperature is the large amount of heat communicated, _by way of
contact_, to the air of the earth's surface; and a fourth and final
cause is the loss endured by the highest strata through radiation into
space.
FOOTNOTES:
[A] The opposite faces of a thermo-electric pile.
[B] See a most interesting paper on this subject by Mr. Hopkins in the
Cambridge 'Transactions,' May, 1856.
[C] See M. Pouillet's important Memoir on Solar Radiation. Taylor's
Scientific Memoirs, vol. iv. p. 44.
ORIGIN OF GLACIERS.
(4.)
[Sidenote: THE SNOW-LINE.]
Having thus accounted for the greater cold of the higher atmospheric
regions, its consequences are next to be considered. One of these is,
that clouds formed in the lower portions of the atmosphere, in warm and
temperate latitudes, usually discharge themselves upon the earth as
rain; while those formed in the higher regions discharge themselves upon
the mountains as snow. The snow of the higher atmosphere is often melted
to rain in passing through the warmer lower strata: nothing indeed is
more common than to pass, in descending a mountain, from snow to rain;
and I have already referred to a case of this kind. The appearance of
the grassy and pine-clad alps, as seen from the valleys after a wet
night, is often strikingly beautiful; the level at which the snow turned
to rain being distinctly marked upon the slopes. Above this level the
mountains are white, while below it they are green. The eye follows this
_snow-line_ with ease along the mountains, and when a sufficient extent
of country is commanded its regularity is surprising.
The term "snow-line," however, which has been here applied to a local
and temporary phenomenon, is commonly understood to mean something else.
In the case just referred to it marked the place where the supply of
solid matter from the upper atmospheric regions, during a single fall,
was exactly equal to its consumption; but the term is usually understood
to mean the line along which the quantity of snow which falls _annually_
is melted, and no more. Below this line each year's snow is completely
cleared away by the summer heat; above it a residual layer abides,
which gradually augments in thickness from the snow-line upwards.
[Sidenote: MOUNTAINS UNLOADED BY GLACIERS.]
Here then we have a fresh layer laid on every year; and it is evident
that, if this process continued without interruption, every mountain
which rises above the snow-line must augment annually in height; the
waters of the sea thus piled, in a solid form, upon the summits of the
hills, would raise the latter to an indefinite elevation. But, as might
be expected, the snow upon steep mountain-sides frequently slips and
rolls down in avalanches into warmer regions, where it is reduced to
water. A comparatively small quantity of the snow is, however, thus got
rid of, and the great agent which Nature employs to relieve her
overladen mountains is the glaciers.
Let us here avoid an error which may readily arise out of the foregoing
reflections. The principal region of clouds and rain and snow extends
only to a limited distance upwards in the atmosphere; the highest
regions contain very little moisture, and were our mountains
sufficiently lofty to penetrate those regions, the quantity of snow
falling upon their summits would be too trifling to resist the direct
action of the solar rays. These would annually clear the summits to a
certain level, and hence, were our mountains high enough, we should have
a superior, as well as an inferior, snow-line; the region of perpetual
snow would form a belt, below which, in summer, snowless valleys and
plains would extend, and above which snowless summits would rise.
(5.)
[Sidenote: WHITE AND BLUE ICE.]
At its origin then a glacier is snow--at its lower extremity it is ice.
The blue blocks that arch the source of the Arveiron were once powdery
snow upon the slopes of the Col du Géant. Could our vision penetrate
into the body of the glacier, we should find that the change from white
to blue essentially consists in the gradual expulsion of the air which
was originally entangled in the meshes of the fallen snow. Whiteness
always results from the intimate and irregular mixture of air and a
transparent solid; a crushed diamond would resemble snow; if we pound
the most transparent rock-salt into powder we have a substance as white
as the whitest culinary salt; and the colourless glass vessel which
holds the salt would also, if pounded, give a powder as white as the
salt itself. It is a law of light that in passing from one substance to
another possessing a different power of refraction, a portion of it is
always reflected. Hence when light falls upon a transparent solid mixed
with air, at each passage of the light from the air to the solid and
from the solid to the air a portion of it is reflected; and, in the case
of a powder, this reflection occurs so frequently that the passage of
the light is practically cut off. Thus, from the mixture of two
perfectly transparent substances, we obtain an opaque one; from the
intimate mixture of air and water we obtain foam; clouds owe their
opacity to the same principle; and the condensed steam of a locomotive
casts a shadow upon the fields adjacent to the line, because the
sunlight is wasted in echoes at the innumerable limiting surfaces of
water and air.
[Sidenote: AIR-BUBBLES IN ICE.]
The snow which falls upon high mountain-eminences has often a
temperature far below the freezing point of water. Such snow is _dry_,
and if it always continued so the formation of a glacier from it would
be impossible. The first action of the summer's sun is to raise the
temperature of the superficial snow to 32°, and afterwards to melt it.
The water thus formed percolates through the colder mass underneath, and
this I take to be the first active agency in expelling the air
entangled in the snow. But as the liquid trickles over the surfaces of
granules colder than itself it is partially deposited in a solid form on
these surfaces, thus augmenting the size of the granules, and cementing
them together. When the mass thus formed is examined, the air within it
is found as _round bubbles_. Now it is manifest that the air caught in
the irregular interstices of the snow can have no tendency to assume
this form so long as the snow remains solid; but the process to which I
have referred--the saturation of the lower portions of the snow by the
water produced by the melting of the superficial portions--enables the
air to form itself into globules, and to give the ice of the _névé_ its
peculiar character. Thus we see that, though the sun cannot get directly
at the deeper portions of the snow, by liquefying the upper layer he
charges it with heat, and makes it his messenger to the cold subjacent
mass.
The frost of the succeeding winter may, I think, or may not, according
to circumstances, penetrate through this layer, and solidify the water
which it still retains in its interstices. If the winter set in with
clear frosty weather, the penetration will probably take place; but if
heavy snow occur at the commencement of winter, thus throwing a
protective covering over the _névé_, freezing to any great depth may be
prevented. Mr. Huxley's idea seems to be quite within the range of
possibility, that water-cells may be transmitted from the origin of the
glacier to its end, retaining their contents always liquid.
[Sidenote: SNOW PRESSED TO ICE.]
It was formerly supposed, and is perhaps still supposed by many, that
the snow of the mountains is converted into the ice of the glacier by
the process of saturation and freezing just indicated. But the frozen
layer would not yet resemble glacier ice; it is only at the deeper
portions of the _névé_ that we find an approximation to the true ice of
the glacier. This brings us to the second great agent in the process of
glacification, namely, pressure. The ice of the _névé_ at 32° may be
squeezed or crushed with extreme facility; and if the force be applied
slowly and with caution, the yielding of the mass may be made to
resemble the yielding of a plastic body. In the depths of the _névé_,
where each portion of the ice is surrounded by a resistant mass, rude
crushing is of course out of the question. The layers underneath yield
with extreme slowness to the pressure of the mass above them; they are
squeezed, but not rudely fractured; and even should rude fracture occur,
the ice, as shall subsequently be shown, possesses the power of
restoring its own continuity. Thus, then, the lower portions of the
_névé_ are removed by pressure more and more from the condition of snow,
the air-bubbles which give to the _névé_-ice its whiteness are more and
more expelled, and this process, continued throughout the entire
glacier, finally brings the ice to that state of magnificent
transparency which we find at the termination of the glacier of
Rosenlaui and elsewhere. This is all capable of experimental proof. The
Messrs. Schlagintweit compressed the snow of the _névé_ to compact ice;
and I have myself frequently obtained slabs of ice from snow in London.
COLOUR OF WATER AND ICE.
(6.)
The sun is continually sending forth waves of different lengths, all of
which travel with the same velocity through the ether. When these waves
enter a prism of glass they are retarded, but in different degrees. The
shorter waves suffer the greatest retardation, and in consequence of
this are most deflected from their straight course. It is this property
which enables us to separate one from the other in the solar spectrum,
and this separation proves that the waves are by no means inextricably
entangled with each other, but that they travel independently through
space.
In consequence of this independence, the same body may intercept one
system of waves while it allows another to pass: on this quality,
indeed, depend all the phenomena of colour. A red glass, for example, is
red because it is so constituted that it destroys the shorter waves
which produce the other colours, and transmits only the waves which
produce red. I may remark, however, that scarcely any glass is of a pure
colour; along with the predominant waves, some of the other waves are
permitted to pass. The colours of flowers are also very impure; in fact,
to get pure colours we must resort to a delicate prismatic analysis of
white light.
[Sidenote: LONG WAVES MOST ABSORBED.]
It has already been stated that a layer of water less than the twentieth
of an inch in thickness suffices to stop and destroy all waves of
radiant heat emanating from an obscure source. The longer waves of the
obscure heat cannot get through water, and I find that all transparent
compounds which contain _hydrogen_ are peculiarly hostile to the longer
undulations. It is, I think, the presence of this element in the
humours of the eye which prevents the extra red rays of the solar
spectrum from reaching the retina. It is interesting to observe that
while bisulphide of carbon, chloride of phosphorus, and other liquids
which contain no hydrogen, permit a large portion of the rays emanating
from an iron or copper ball, at a heat below redness, to pass through
them with facility, the same thickness of substances equally
transparent, but which contain hydrogen, such as ether, alcohol, water,
or the vitreous humour of the eye of an ox, completely intercepts these
obscure rays. The same is true of solid bodies; a very slight thickness
of those which contain hydrogen offers an impassable barrier to all rays
emanating from a non-luminous source.[A] But the heat thus intercepted
is by no means lost; its _radiant form_ merely is destroyed. Its waves
are shivered upon the particles of the body, but they impart warmth to
it, while the heat which retains its radiant form contributes in no way
to the warmth of the body through which it passes.
[Sidenote: FINAL COLOUR OF ICE AND WATER BLUE.]
Water then absorbs all the extra red rays of the sun, and if the layer
be thick enough it invades the red rays themselves. Thus the greater the
distance the solar beams travel through pure water the more are they
deprived of those components which lie at the red end of the spectrum.
The consequence is, that the light finally transmitted by the water, and
which gives to it its colour, is _blue_.
[Sidenote: EXPERIMENT.]
I find the following mode of examining the colour of water both
satisfactory and convenient:--A tin tube, fifteen feet long and three
inches in diameter, has its two ends stopped securely by pieces of
colourless plate glass. It is placed in a horizontal position, and pure
water is poured into it through a small lateral pipe, until the liquid
reaches half way up the glasses at the ends; the tube then holds a
semi-cylinder of water and a semi-cylinder of air. A white plate, or a
sheet of white paper, well illuminated, is then placed at a little
distance from one end of the tube, and is looked at through the tube.
Two semicircular spaces are then seen, one by the light which has passed
through the air, the other by the light which has passed through the
water; and their proximity furnishes a means of comparison, which is
absolutely necessary in experiments of this kind. It is always found
that, while the former semicircle remains white, the latter one is
vividly coloured.[B]
When the beam from an electric lamp is sent through this tube, and a
convex lens is placed at a suitable distance from its most distant end,
a magnified image of the coloured and uncoloured semicircles may be
projected upon a screen. Tested thus, I have sometimes found, after
rain, the ordinary pipe-water of the Royal Institution quite opaque;
while, under other circumstances, I have found the water of a clear
green. The pump-water of the Institution thus examined exhibits a rich
sherry colour, while distilled water is blue-green.
The blueness of the Grotto of Capri is due to the fact that the light
which enters it has previously traversed a great depth of clear water.
According to Bunsen's account, the _laugs_, or cisterns of hot water, in
Iceland must be extremely beautiful. The water contains silica in
solution, which, as the walls of the cistern arose, was deposited upon
them in fantastic incrustations. These, though white, when looked at
through the water appear of a lovely blue, which deepens in tint as the
vision plunges deeper into the liquid.
[Sidenote: ICE OPAQUE TO RADIANT HEAT.]
Ice is a crystal formed from this blue liquid, the colour of which it
retains. Ice is the most opaque of transparent solids to radiant heat,
as water is the most opaque of liquids. According to Melloni, a plate of
ice one twenty-fifth of an inch thick, which permits the rays of light
to pass without sensible absorption, cuts off 94 per cent. of the rays
of heat issuing from a powerful oil lamp, 99-1/2 per cent. of the rays
issuing from incandescent platinum, and the whole of the rays issuing
from an obscure source. The above numbers indicate how large a portion
of the rays emitted by our artificial sources of light is obscure.
When the rays of light pass through a sufficient thickness of ice the
longer waves are, as in the case of water, more and more absorbed, and
the final colour of the substance is therefore blue. But when the ice is
filled with minute air-bubbles, though we should loosely call it
_white_, it may exhibit, even in small pieces, a delicate blue tint.
This, I think, is due to the frequent interior reflection which takes
place at the surfaces of the air-cells; so that the light which reaches
the eye from the interior may, in consequence of its having been
reflected hither and thither, really have passed through a considerable
thickness of ice. The same remark, as we have already seen, applies to
the delicate colour of newly fallen snow.
FOOTNOTES:
[A] What is here stated regarding hydrogen is true of all the liquids
and solids which have hitherto been examined,--but whether any
exceptions occur, future experience must determine. It is only when in
combination that it exhibits this impermeability to the obscure rays.
[B] In my own experiments I have never yet been able to obtain a pure
blue, the nearest approach to it being a blue-green.
COLOURS OF THE SKY.
(7.)
[Sidenote: NEWTON'S HYPOTHESIS.]
In treating of the Colours of Thin Plates we found that a certain
thickness was necessary to produce blue, while a greater thickness was
necessary for red. With that wonderful power of generalization which
belonged to him, Newton thus applies this apparently remote fact to the
blue of the sky:--"The blue of the first order, though very faint and
little, may possibly be the colour of some substances, and particularly
the azure colour of the skies seems to be of this order. For all
vapours, when they begin to condense and coalesce into small parcels,
become first of that bigness whereby such an azure is reflected, before
they can constitute clouds of other colours. And so, this being the
first colour which vapours begin to reflect, it ought to be the colour
of the finest and most transparent skies, in which vapours are not
arrived at that grossness requisite to reflect other colours, as we find
it is by experience."
M. Clausius has written a most interesting paper, which he endeavours to
show that the minute particles of water which are supposed by Newton to
reflect the light, cannot be little globes entirely composed of water,
but bladders or hollow spheres; the vapour must be in what is generally
termed the _vesicular_ state. He was followed by M. Brücke, whose
experiments prove that the suspended particles may be so small that the
reasoning of M. Clausius may not apply to them.
But why need we assume the existence of such particles at all?--why not
assume that the colour of the air is blue, and renders the light of the
sun blue, after the fashion of a blue glass or a solution of the
sulphate of copper? I have already referred to the great variation which
the colour of the firmament undergoes in the Alps, and have remarked
that this seems to indicate that the blue depends upon some variable
constituent of the atmosphere. Further, we find that the blue light of
the sky is _reflected_ light; and there must be something in the
atmosphere capable of producing this reflection; but this thing,
whatever it is, produces another effect which the blue glass or liquid
is unable to produce. These _transmit_ blue light, whereas, when the
solar beams have traversed a great length of air, as in the morning or
the evening, they are yellow, or orange, or even blood-red, according to
the state of the atmosphere:--the transmitted light and the reflected
light of the atmosphere are then totally different in colour.
[Sidenote: GOETHE'S HYPOTHESIS.]
Goethe, in his celebrated 'Farbenlehre,' gives a theory of the colour of
the sky, and has illustrated it by a series of striking facts. He
assumed two principles in the universe--Light and Darkness--and an
intermediate stage of Turbidity. When the darkness is seen through a
turbid medium on which the light falls, the medium appears blue; when
the light itself is viewed through such a medium, it is yellow, or
orange, or ruby-red. This he applies to the atmosphere, which sends us
blue light, or red, according as the darkness of infinite space, or the
bright surface of the sun, is regarded through it.
As a theory of colours Goethe's work is of no value, but the facts which
he has brought forward in illustration of the action of turbid media are
in the highest degree interesting. He refers to the blueness of distant
mountains, of smoke, of the lower part of the flame of a candle (which
if looked at with a white surface behind it completely disappears), of
soapy water, and of the precipitates of various resins in water. One of
his anecdotes in connexion with this subject is extremely curious and
instructive. The portrait of a very dignified theologian having suffered
from dirt, it was given to a painter to be cleaned. The clergyman was
drawn in a dress of black velvet, over which the painter, in the first
place, passed his sponge. To his astonishment the black velvet changed
to the colour of blue plush, and completely altered the aspect of its
wearer. Goethe was informed of the fact; the experiment was repeated in
his presence, and he at once solved it by reference to his theory. The
varnish of the picture when mixed with the water formed a turbid medium,
and the black coat seen through it appeared blue; when the water
evaporated the coat resumed its original aspect.
[Sidenote: SUSPENDED PARTICLES.]
With regard to the real explanation of these effects, it may be shown,
that, if a beam of white light be sent through a liquid which contains
extremely minute particles in a state of suspension, the short waves are
more copiously reflected by such particles than the long ones; blue, for
example, is more copiously reflected than red. This may be shown by
various fine precipitates, but the best is that of Brücke. We know that
mastic and various resins are soluble in alcohol, and are precipitated
when the solution is poured into water: _Eau de Cologne_, for example,
produces a white precipitate when poured into water. If however this
precipitate be sufficiently diluted, it gives the liquid a bluish colour
by reflected light. Even when the precipitate is very thick and gross,
and floats upon the liquid like a kind of curd, its under portions often
exhibit a fine blue. To obtain particles of a proper size, Brücke
recommends 1 gramme of colourless mastic to be dissolved in 87 grammes
of alcohol, and dropped into a beaker of water, which is kept in a state
of agitation. In this way a blue resembling that of the firmament may be
produced. It is best seen when a black cloth is placed behind the glass;
but in certain positions this blue liquid appears yellow; and these are
the positions when the _transmitted_ light reaches the eye. It is
evident that this change of colour must necessarily exist; for the blue
being partially withdrawn by more copious reflection, the transmitted
light must partake more or less of the character of the complementary
colour; though it does not follow that they should be exactly
complementary to each other.
[Sidenote: THE SUN THROUGH LONDON SMOKE.]
When a long tube is filled with clear water, the colour of the liquid,
as before stated, shows itself by transmitted light. The effect is very
interesting when a solution of mastic is permitted to drop into such a
tube, and the fine precipitate to diffuse itself in the water. The
blue-green of the liquid is first neutralized, and a yellow colour shows
itself; on adding more of the solution the colour passes from yellow to
orange, and from orange to blood-red. With a cell an inch and a half in
width, containing water, into which the solution of mastic is suffered
to drop, the same effect may be obtained. If the light of an electric
lamp be caused to form a clear sunlike disk upon a white screen, the
gradual change of this light by augmented precipitation into deep
glowing red, resembling the colour of the sun when seen through fine
London smoke, is exceedingly striking. Indeed the smoke acts, in some
measure, the part of our finely-suspended matter.
[Sidenote: MORNING AND EVENING RED.]
By such means it is possible to imitate the phenomena of the firmament;
we can produce its pure blue, and cause it to vary as in nature. The
milkiness which steals over the heavens, and enables us to distinguish
one cloudless day from another, can be produced with the greatest ease.
The yellow, orange, and red light of the morning and evening can also be
obtained: indeed the effects are so strikingly alike as to suggest a
common origin--that the colours of the sky are due to minute particles
diffused through the atmosphere. These particles are doubtless the
condensed vapour of water, and its variation in quality and amount
enables us to understand the variability of the firmamental blue, and of
the morning and the evening red. Professor Forbes, moreover, has made
the interesting observation that the steam of a locomotive, at a certain
stage of its condensation, is blue or red according as it is viewed by
reflected or transmitted light.
These considerations enable us to account for a number of facts of
common occurrence. Thin milk, when poured upon a black surface, appears
bluish. The milk is colourless; that is, its blueness is not due to
_absorption_, but to a _separation_ of the light by the particles
suspended in the liquid. The juices of various plants owe their blueness
to the same cause; but perhaps the most curious illustration is that
presented by a blue eye. Here we have no true colouring matter, no
proper absorption; but we look through a muddy medium at the black
choroid coat within the eye, and the medium appears blue.[A]
[Sidenote: COLOUR OF SWISS LAKES.]
Is it not probable that this action of finely-divided matter may have
some influence on the colour of some of the Swiss lakes--as that of
Geneva for example? This lake is simply an expansion of the river Rhone,
which rushes from the end of the Rhone glacier, as the Arveiron does
from the end of the Mer de Glace. Numerous other streams join the Rhone
right and left during its downward course; and these feeders, being
almost wholly derived from glaciers, join the Rhone charged with the
finer matter which these in their motion have ground from the rocks over
which they have passed. But the glaciers must grind the mass beneath
them to particles of all sizes, and I cannot help thinking that the
finest of them must remain suspended in the lake throughout its entire
length. Faraday has shown that a precipitate of gold may require months
to sink to the bottom of a bottle not more than five inches high, and
in all probability it would require _ages_ of calm subsidence to bring
_all_ the particles which the Lake of Geneva contains to its bottom. It
seems certainly worthy of examination whether such particles suspended
in the water contribute to the production of that magnificent blue which
has excited the admiration of all who have seen it under favourable
circumstances.
FOOTNOTES:
[A] Helmholtz, 'Das Sehen des Menschen.'
THE MORAINES.
(8.)
The surface of the glacier does not long retain the shining whiteness of
the snow from which it is derived. It is flanked by mountains which are
washed by rain, dislocated by frost, riven by lightning, traversed by
avalanches, and swept by storms. The lighter débris is scattered by the
winds far and wide over the glacier, sullying the purity of its surface.
Loose shingle rattles at intervals down the sides of the mountains, and
falls upon the ice where it touches the rocks. Large rocks are
continually let loose, which come jumping from ledge to ledge, the
cohesion of some being proof against the shocks which they experience;
while others, when they hit the rocks, burst like bomb-shells, and
shower their fragments upon the ice.
[Sidenote: LATERAL MORAINES.]
Thus the glacier is incessantly loaded along its borders with the ruins
of the mountains which limit it; and it is evident that the quantity of
rock and rubbish thus cast upon the glacier depends upon the character
of the adjacent mountains. Where the summits are bare and friable, we
may expect copious showers; where they are resistant, and particularly
where they are protected by a covering of ice and snow, the quantity
will be small. As the glacier moves downward, it carries with it the
load deposited upon it. Long ridges of débris thus flank the glacier,
and these ridges are called _lateral moraines_. Where two tributary
glaciers join to form a trunk-glacier, their adjacent lateral moraines
are laid side by side at the place of confluence, thus constituting a
ridge which runs along the middle of the trunk-glacier, and which is
called a _medial moraine_. The rocks and débris carried down by the
glacier are finally deposited at its lower extremity, forming there a
_terminal moraine_.
[Sidenote: MEDIAL AND TERMINAL MORAINES.]
It need hardly be stated that the number of medial moraines is only
limited by the number of branch glaciers. If a glacier have but two
branches, it will have only one medial moraine; if it have three
branches, it will have two medial moraines; if _n_ branches, it will
have _n_-1 medial moraines. The number of medial moraines, in short, is
always _one less_ than the number of branches. A glance at the annexed
figure will reveal the manner in which the lateral moraines of the Mer
de Glace unite to form medial ones. (See Fig. 19.)
[Illustration: MORAINES OF THE MER DE GLACE.
Fig. 19. _To face p. 264_.]
When a glacier diminishes in size it leaves its lateral moraines
stranded on the flanks of the valleys. Successive shrinkings may thus
occur, and _have_ occurred at intervals of centuries; and a succession
of old lateral moraines, such as many glacier-valleys exhibit, is the
consequence. The Mer de Glace, for example, has its old lateral
moraines, which run parallel with its present ones. The glacier may also
diminish _in length_ at distant intervals; the result being a succession
of more or less concentric terminal moraines. In front of the
Rhone-glacier we have six or seven such moraines, and the Mer de Glace
also possesses a series of them.
Let us now consider the effect produced by a block of stone upon the
surface of a glacier. The ice around it receives the direct rays of the
sun, and is acted on by the warm air; it is therefore constantly
melting. The stone also receives the solar beams, is warmed, and
transmits its heat, by conduction, to the ice beneath it. If the heat
thus transmitted to the ice through the stone be less than an equal
space of the surrounding ice receives, it is manifest that the ice
around the stone will waste more quickly than that beneath it, and the
consequence is, that, as the surface sinks, it leaves behind it a
pillar of ice, on which the block is elevated. If the stone be wide and
flat, it may rise to a considerable height, and in this position it
constitutes what is called a glacier-_table_. (See Fig. 6.)
[Sidenote: GLACIER TABLES ACCOUNTED FOR.]
Almost all glaciers present examples of such tables; but no glacier with
which I am acquainted exhibits them in greater number and perfection
than the Unteraar glacier, near the Grimsel. Vast masses of granite are
thus poised aloft on icy pedestals; but a limit is placed to their
exaltation by the following circumstance. The sun plays obliquely upon
the table all day; its southern extremity receives more heat than its
northern, and the consequence is, that it _dips_ towards the south.
Strictly speaking, the plane of the dip rotates a little during the day,
being a little inclined towards the east in the morning, north and south
a little after noon, and inclined towards the west in the evening; so
that, theoretically speaking, the block is a sun-dial, showing by its
position the hour of the day. This rotation is, however, too small to be
sensible, and hence _the dip of the stones upon a glacier sufficiently
exposed to the sunlight, enables us at any time to draw the meridian
line along its surface_. The inclination finally becomes so great that
the block slips off its pedestal, and begins to form another, while the
one which it originally occupied speedily disappears, under the
influence of sun and air. Fig. 20 represents a typical section of a
glacier-table, the sun's rays being supposed to fall in the direction of
the shading lines.
[Sidenote: TYPE "TABLE."]
[Illustration: Fig. 20. Typical section of a glacier Table.]
Stones of a certain size are always lifted in the way described. A
considerable portion of the heat which a large block receives is wasted
by radiation, and by communication to the air, so that the quantity
which reaches the ice beneath is trifling. Such a mass is, of course, a
protector of the ice beneath it. But if the stone be small, and dark in
colour, it absorbs the heat with avidity, communicates it quickly to
the ice with which it is in contact, and consequently sinks in the ice.
This is also the case with bits of dirt and the finer fragments of
débris; they sink in the glacier. Sometimes, however, a pretty thick
layer of sand is washed over the ice from the moraines, or from the
mountain-sides; and such sand-layers give birth to ice-cones, which grow
to peculiarly grand dimensions on the Lower Aar glacier. I say "grow,"
but the truth, of course, is, that the surrounding ice wastes, while the
portion underneath the sand is so protected that it remains as an
eminence behind. At first sight, these sand-covered cones appear huge
heaps of dirt, but on examination they are found to be cones of ice, and
that the dirt constitutes merely a superficial covering.
Turn we now to the moraines. Protecting, as they do, the ice from waste,
they rise, as might be expected, in vast ridges above the general
surface of the glacier. In some cases the surrounding mass has been so
wasted as to leave the spines of ice which support the moraines forty or
fifty feet above the general level of the glacier. I should think the
moraines of the Mer de Glace about the Tacul rise to this height. But
lower down, in the neighbourhood of the Echelets, these high ridges
disappear, and nought remains to mark the huge moraine but a strip of
dirt, and perhaps a slight longitudinal protuberance on the surface of
the glacier. How have the blocks vanished that once loaded the moraines
near the Tacul? They have been swallowed in the crevasses which
intersect the moraines lower down; and if we could examine the ice at
the Echelets we should find the engulfed rocks in the body of the
glacier.
[Sidenote: MORAINES ENGULFED AND DISGORGED.]
Cases occur, wherein moraines, after having been engulfed, and hidden
for a time, are again entirely disgorged by the glacier. Two moraines
run along the basin of the Talèfre, one from the Jardin, the other from
an adjacent promontory, proceeding parallel to each other towards the
summit of the great ice-fall. Here the ice is riven, and profound chasms
are formed, in which the blocks and shingle of the moraines disappear.
Throughout the entire ice-fall the only trace of the moraines is a broad
dirt-streak, which the eye may follow along the centre of the fall, with
perhaps here and there a stone which has managed to rise from its frozen
sepulchre. But the ice wastes, and at the base of the fall large masses
of stone begin to reappear; these become more numerous as we descend;
the smaller débris also appears, and finally, at some distance below the
fall, the moraine is completely restored, and begins to exercise its
protecting influence; it rises upon its ridge of ice, and dominates as
before over the surface of the glacier.
[Sidenote: TRANSPARENCY OF ICE UNDER THE MORAINES.]
The ice under the moraines and sand-cones is of a different appearance
from that of the surrounding glacier, and the principles we have laid
down enable us to explain the difference. The sun's rays, striking upon
the unprotected surface of the glacier, enter the ice to a considerable
depth; and the consequence is, that the ice near the surface of the
glacier is always disintegrated, being cut up with minute fissures and
cavities, filled with water and air, which, for reasons already
assigned, cause the glacier, when it is clean, to appear white and
opaque. The ice under the moraines, on the contrary, is usually dark and
transparent; I have sometimes seen it as black as pitch, the blackness
being a proof of its great transparency, which prevents the reflection
of light from its interior.
The ice under the moraines cannot be assailed in its depths by the solar
heat, because this heat becomes _obscure_ before it reaches the ice, and
as such it lacks the power of penetrating the substance. It is also
communicated in great part by way of contact instead of by radiation. A
thin film at the surface of the moraine-ice engages all the heat that
acts upon it, its deeper portions remaining intact and transparent.
GLACIER MOTION.
PRELIMINARY.
(9.)
[Sidenote: NÉVÉ AND GLACIER.]
Though a glacier is really composed of two portions, one above and the
other below the snow-line, the term glacier is usually restricted to the
latter, while the French term _névé_ is applied to the former. It is
manifest that the snow which falls upon the glacier proper can
contribute nothing to its growth or permanence; for every summer is not
only competent to abolish the accumulations of the foregoing winter, but
to do a great deal more. During each summer indeed a considerable
quantity of the ice below the snow-line is reduced to water; so that, if
the waste were not in some way supplied, it is manifest that in a few
years the lower portion of the glacier must entirely disappear. The end
of the Mer de Glace, for example, could never year after year thrust
itself into the valley of Chamouni, were there not some agency by which
its manifest waste is made good. This agency is the motion of the
glacier.
To those unacquainted with the fact of their motion, but who have stood
upon these vast accumulations of ice, and noticed their apparent fixity
and rigidity, the assertion that a glacier moves must appear in the
highest degree startling and incredible. They would naturally share the
doubts of a certain professor of Tübingen, who, after a visit to the
glaciers of Switzerland, went home and wrote a book flatly denying the
possibility of their motion. But reflection comes to the aid of sense,
and qualifies first impressions. We ask ourselves how is the permanence
of the glacier secured? How are the moraines to be accounted for?
Whence come the blocks which we often find at the terminus of a glacier,
and which we know belong to distant mountains? The necessity of motion
to produce these results becomes more and more apparent, until at length
we resort to actual experiment. We take two fixed points at opposite
sides of the glacier, so that a block of stone which rests upon the ice
may be in the straight line which unites the points; and we soon find
that the block quits the line, and is borne downwards by the glacier. We
may well realize the interest of the man who first engaged in this
experiment, and the pleasure which he felt on finding that the block
moved; for even now, after hundreds of observations on the motion of
glaciers have been made, the actual observance of this motion for the
first time is always accompanied by a thrill of delight. Such pleasure
the direct perception of natural truth always imparts. Like Antæus we
touch our mother, and are refreshed by the contact.
[Sidenote: HUGI'S MEASUREMENTS.]
The fact of glacier-motion has been known for an indefinite time to the
inhabitants of the mountains; but the first who made quantitative
observations of the motion was Hugi. He found that from 1827 to 1830 his
cabin upon the glacier of the Aar had moved 100 mètres, or about 110
yards, downwards; in 1836 it had moved 714 mètres; and in 1841 M.
Agassiz found it at a distance of 1,428 mètres from its first position.
This is equivalent in round numbers to an average velocity of 100 mètres
a year. In 1840 M. Agassiz fixed the position of the rock known as the
Hôtel des Neufchâtelois; and on the 5th of September, 1841, he found
that it had moved 213 feet downward. Between this date and September,
1842, the rock moved 273 feet, thus accomplishing a distance of 486 feet
in two years.
But much uncertainty prevailed regarding the motion of the boulders, for
they sometimes rolled upon the glacier, and hence it was resolved to
use stakes of wood driven into the ice. In the month of July, 1841, M.
Escher de la Linth fixed a system of stakes, every two of which were
separated from each other by a distance of 100 mètres, across the great
Aletsch glacier. A considerable number of other stakes were fixed
_along_ the glacier, the longitudinal separation being also 100 mètres.
On the 8th of July the stakes stood at a depth of about three feet in
the ice. On the 16th of August he returned to the glacier. Almost all
the stakes had fallen, and no trace, even of the holes in which they had
been sunk, remained. M. Agassiz was equally unsuccessful on the glacier
of the Aar. It must therefore be borne in mind, that, previous to the
introduction of the facile modes of measurement which we now employ,
severe labour and frequent disappointment had taught observers the true
conditions of success.
After his defeat upon the Aletsch, M. Escher joined MM. Agassiz and
Desor on the Aar glacier, where, between the 31st of August and the 5th
of September, they fixed in concert the positions of a series of blocks
upon the ice, with the view of measuring their displacements the
following year.
[Sidenote: AGASSIZ'S MEASUREMENTS.]
Another observation of great importance was also commenced in 1841.
Warned by previous failures, M. Agassiz had iron boring-rods carried up
the glacier, with which he pierced the ice at six places to a depth of
ten feet, and at each place drove a wooden pile into the ice. These six
stations were in the same straight line across the glacier; three of
them standing upon the Finsteraar and three on the Lauteraar tributary.
About this time also M. Agassiz conceived the idea of having the
displacements measured the year following with precise instruments, and
also of having constructed, by a professional engineer, a map of the
entire glacier, on which all its visible "accidents" should be drawn
according to scale. This excellent work was afterwards executed by M.
Wild, now Professor of Geodesy and Topography in the Polytechnic School
of Zürich, and it is published as a separate atlas in connexion with M.
Agassiz's 'Système Glaciaire.'
[Sidenote: PROF. J. D. FORBES INVITED.]
M. Agassiz is a naturalist, and he appears to have devoted but little
attention to the study of physics. At all events, the physical portions
of his writings appear to me to be very often defective. It was probably
his own consciousness of this deficiency that led him to invoke the
advice of Arago and others previous to setting out upon his excursions.
It was also his desire "to see a philosopher so justly celebrated occupy
himself with the subject," which induced him to invite Prof. J. D.
Forbes of Edinburgh to be his guest upon the Aar glacier in 1841. On the
8th of August they met at the Grimsel Hospice, and for three weeks
afterwards they were engaged together daily upon the ice, sharing at
night the shelter of the same rude roof. It is in reference to this
visit that Prof. Forbes writes thus at page 38 of the 'Travels in the
Alps':--"Far from being ready to admit, as my sanguine companions wished
me to do in 1841, that the theory of glaciers was complete, and the
cause of their motion certain, after patiently hearing all they had to
say and reserving my opinion, I drew the conclusion that no theory which
I had then heard of could account for the few facts admitted on all
hands." In 1842 Prof. Forbes repaired, as early as the state of the snow
permitted, to the Mer de Glace; he worked there, in the first instance,
for a week, and afterwards crossed over to Courmayeur to witness a solar
eclipse. The result of his week's observations was immediately
communicated to Prof. Jameson, then editor of the 'Edinburgh New
Philosophical Journal.'
[Sidenote: CENTRE MOVES QUICKEST.]
In that letter he announces the fact, but gives no details of the
measurement, that "the central part of the glacier moves faster than the
edges in a very considerable proportion; quite contrary to the opinion
generally entertained." He also announced at the same time the
continuous hourly advance of the glacier. This letter bears the date,
"Courmayeur, Piedmont, 4th July," but it was not published until the
month of October following.
Meanwhile M. Agassiz, in company with M. Wild, returned to complete his
experiment upon the glacier of the Aar. On the 20th of July, 1842, the
displacements of the six piles which he had planted the year before were
determined by means of a theodolite. Of the three upon the Finsteraar
affluent, that nearest the side had moved 160 feet, the next 225 feet,
while that nearest to the centre had moved 269 feet. Of those on the
Lauteraar, that nearest the side had moved 125 feet, the next 210 feet,
and that nearest the centre 246 feet. These observations were perfectly
conclusive as to the quicker motion of the centre: they embrace a year's
motion; and the magnitude of the displacements, causing errors of
inches, which might seriously affect small displacements, to vanish,
justifies us in ranking this experiment with the most satisfactory of
the kind that have ever been made. The results were communicated to
Arago in a letter dated from the glacier of the Aar, on the 1st of
August, 1842; they were laid before the Academy of Sciences on the 29th
of August, 1842, and are published in the 'Comptes Rendus' of the same
date.
The facts, then, so far as I have been able to collect them, are as
follows:--M. Agassiz commenced his experiment about ten months before
Professor Forbes, and the results of his measurements, with quantities
stated, were communicated to the French Academy about two months prior
to the publication of the letter of Professor Forbes in the 'Edinburgh
Philosophical Journal.' But the latter communication, announcing in
general terms the fact of the speedier central motion, was dated from
Courmayeur twenty-seven days before the date of M. Agassiz's letter
from the glacier of the Aar.
[Sidenote: STATE OF THE QUESTION.]
The speedier motion of the central portion of a glacier has been justly
regarded as one of cardinal importance, and no other observation has
been the subject of such frequent reference; but the general impression
in England is that M. Agassiz had neither part nor lot in the
establishment of the above fact; and in no English work with which I am
acquainted can I find any reference to the above measurements. Relying
indeed upon such sources for my information, I remained ignorant of the
existence of the paper in the 'Comptes Rendus' until my attention was
directed to it by Professor Wheatstone. In the next following chapters I
shall have to state the results of some of my own measurements, and
shall afterwards devote a little time to the consideration of the cause
of glacier-motion. In treating a question on which so much has been
written, it is of course impossible, as it would be undesirable, to
avoid subjecting both my own views and those of others to a critical
examination. But in so doing I hope that no expression shall escape me
inconsistent with the courtesy which ought to be habitual among
philosophers or with the frank recognition of the just claims of my
predecessors.
MOTION OF THE MER DE GLACE.
(10.)
[Sidenote: MY FIRST OBSERVATION.]
On Tuesday, the 14th of July, 1857, I made my first observation on the
motion of the Mer de Glace. Accompanied by Mr. Hirst I selected on the
steep slope of the Glacier des Bois a straight pinnacle of ice, the
front edge of which was perfectly vertical. In coincidence with this
edge I fixed the vertical fibre of the theodolite, and permitted the
instrument to stand for three hours. On looking through it at the end of
this interval, the cross hairs were found projected against the white
side of the pyramid; the whole mass having moved several inches
downwards.
The instrument here mentioned, which had long been in use among
engineers and surveyors, was first applied to measure glacier-motion in
1842; by Prof. Forbes on the Mer de Glace, and by M. Agassiz on the
glacier of the Aar. The portion of the theodolite made use of is easily
understood. The instrument is furnished with a telescope capable of
turning up and down upon a pivot, without the slightest deviation right
or left; and also capable of turning right or left without the slightest
deviation up or down. Within the telescope two pieces of spider's
thread, so fine as to be scarcely visible to the naked eye, are drawn
across the tube and across each other. When we look through the
telescope we see these fibres, their point of intersection being exactly
in the centre of the tube; and the instrument is furnished with screws
by means of which this point can be fixed upon any desired object with
the utmost precision.
[Sidenote: MODE OF MEASUREMENT.]
In setting a straight row of stakes across the glacier, our mode of
proceeding was in all cases this:--The theodolite was placed on the
mountain-side flanking the glacier, quite clear of the ice; and having
determined the direction of a line perpendicular to the axis of the
glacier, a well-defined object was sought at the opposite side of the
valley as close as possible to this direction; the object being, in some
cases, the sharp edge of a cliff; in others, a projecting corner of
rock; and, in others, a well-defined mark on the face of the rock. This
object and those around it were carefully sketched, so that on returning
to the place it could be instantly recognized. On commencing a line the
point of intersection of the two spiders' threads within the telescope
was first fixed accurately upon the point thus chosen, and an assistant
carrying a straight bâton was sent upon the ice. By rough signalling he
first stood near the place where the first stake was to be driven in;
and the object end of the telescope was then lowered until he came
within the field of view. He held his staff upright upon the ice, and,
in obedience to signals, moved upwards or downwards until the point of
intersection of the spiders-threads exactly hit the bottom of the bâton;
a concerted signal was then made, the ice was pierced with an auger to a
depth of about sixteen inches, and a stake about two feet long was
firmly driven into it. The assistant then advanced for some distance
across the glacier; the end of the telescope was now gently raised until
he and his upright staff again appeared in the field of view. He then
moved as before until the bottom of his staff was struck by the point of
intersection, and here a second stake was fixed in the ice. In this way
the process was continued until the line of stakes was completed.
Before quitting the station, a plummet was suspended from a hook
directly underneath the centre of the theodolite, and the place where
the point touched the ground was distinctly marked. To measure the
motion of the line of stakes, we returned to the place a day or two
afterwards, and by means of the plummet were able to make the theodolite
occupy the exact position which it occupied when the line was set out.
The telescope being directed upon the point at the opposite side of the
valley, and gradually lowered, it was found that no single stake along
the line preserved its first position: they had all shifted downwards.
The assistant was sent to the first stake; the point which it had first
occupied was again determined, and its present distance from that point
accurately measured. The same thing was done in the case of each stake,
and thus the displacement of the whole row of stakes was ascertained.[A]
The time at which the stake was fixed, and at which its displacement was
measured, being carefully noted, a simple calculation determined _the
daily motion_ of the stake.
[Sidenote: THE FIRST LINE.]
Thus, on the 17th of July, 1857, we set out our first line across the
Mer de Glace, at some distance below the Montanvert; on the day
following we measured the progress of the stakes. The observed
displacements are set down in the following table:--
First Line.--Daily Motion.
No. of stake. Inches.
West 1 moved 12-1/4
2 " 16-3/4
3 " 22-1/2
4 " ...
5 " 24-1/2
6 moved ...
7 " 26-1/4
8 " ...
9 " 28-3/4
10 " 35-1/2 East.
[Sidenote: THE CENTRE-POINT NOT THE QUICKEST.]
The theodolite in this case stood on the Montanvert side of the valley,
and the stakes are numbered from this side. We see that the motion
gradually augments from the 1st stake onward--the 1st stake being held
back by the friction of the ice against the flanking mountain-side. The
stakes 4, 6, and 8 have no motion attached to them, as an accident
rendered the measurement of their displacements uncertain. But one
remarkable fact is exhibited by this line; the 7th stake stood upon the
_middle_ of the glacier, and we see that its motion is by no means the
quickest; it is exceeded in this respect by the stakes 9 and 10.
The portion of the glacier on which the 10th stake stood was very much
cut up by crevasses, and, while the assistant was boring it with his
auger, the ice beneath him was observed, through the telescope, to slide
suddenly forward for about 4 inches. The other stakes retained their
positions, so that the movement was purely local. Deducting the 4 inches
thus irregularly obtained, we should have a daily motion of 31-1/2
inches for stake No. 10. The place was watched for some time, but the
slipping was not repeated; and a second measurement on the succeeding
day made the motion of the 10th stake 32 inches, whilst that of the
centre of the glacier was only 27.
Here, then, was a fact which needed explanation; but, before attempting
this, I resolved, by repeated measurements in the same locality, to
place the existence of the fact beyond doubt. We therefore ascended to a
point upon the old and now motionless moraine, a little above the
Montanvert Hotel; and choosing, as before, a well-defined object at the
opposite side of the valley, we set between it and the theodolite a row
of twenty stakes across the glacier. Their motions, measured on a
subsequent day, and reduced to their daily rate, gave the results set
down in the following table:--
Second Line.--Daily Motion.
No. of stake. Inches.
West 1 moved 7-1/2
2 " 10-3/4
3 " 12-1/4
4 " 14-1/2
5 " 16
6 " 16-3/4
7 " 17-1/2
8 " 19
9 " 19-1/2
10 " 21
11 moved 21
12 " 22-1/2
13 " 21
14 " 22-1/2
15 " 20-1/2
16 " 21-3/4
17 " 22-1/4
18 " 25-1/4
19 " ...
20 " 25-3/4 East.
[Sidenote: CORROBORATIVE MEASUREMENTS.]
As regards the retardation of the side, we observe here the same fact as
that revealed by our first line--the motion gradually augments from the
first stake to the last. The stake No. 20 stood upon the dirty portion
of the ice, which was derived from the Talèfre tributary of the Mer de
Glace, and far beyond the middle of the glacier. These measurements,
therefore, corroborate that made lower down, as regards the
non-coincidence of the point of swiftest motion with the centre of the
glacier.
But it will be observed that the measurements do not show any
retardation of the ice at the eastern extremity of the line of
stakes--the motion goes on augmenting from the first stake to the last.
The reason of this is, that in neither of the cases recorded were we
able to get the line quite across the glacier; the crevasses and broken
ice-ridges, which intercepted the vision, compelled us to halt before we
came sufficiently close to the eastern side to make its retardation
sensible. But on the 20th of July my friend Hirst sought out an elevated
station on the Chapeau, or eastern side of the valley, whence he could
command a view from side to side over all the humps and inequalities of
the ice, the fixed point at the opposite side, upon which the telescope
was directed, being the corner of a window of the Montanvert Hotel.
Along this line were placed twelve stakes, the daily motions of which
were found to be as follows:--
Third Line.--Daily Motion.
No. of stake. Inches.
East 1 moved 19-1/2
2 " 22-3/4
3 " 28-3/4
4 " 30-1/4
5 " 33-3/4
6 " 28-1/4
7 moved 24-1/2
8 " 25
9 " 25
10 " 18
11 " ...
12 " 8-1/2 West.
The numbering of the stakes along this line commenced from the
Chapeau-side of the glacier, and the retardation of that side is now
manifest enough; the motion gradually augmenting from 19-1/2 to 33-1/2
inches. But, comparing the velocity of the two extreme stakes, we find
that the retardation of stake 12 is much greater than that of stake 1.
Stake 5, moreover, which moved with the _maximum_ velocity, was not upon
the centre of the glacier, but much nearer to the eastern than to the
western side.
[Sidenote: A NEW PECULIARITY OF GLACIER MOTION.]
It was thus placed beyond doubt that the point of maximum motion of the
Mer de Glace, at the place referred to, is not the centre of the
glacier. But, to make assurance doubly sure, I examined the comparative
motion along three other lines, and found in all the same undeviating
result.
This result is not only unexpected, but is quite at variance with the
opinions hitherto held regarding the motion of the Mer de Glace. The
reader knows that the trunk-stream is composed of three great
tributaries from the Géant, the Léchaud, and the Talèfre. The Glacier du
Géant fills more than half of the trunk-valley, and the junction between
it and its neighbours is plainly marked by the dirt upon the surface of
the latter. In fact four medial moraines are crowded together on the
eastern side of the glacier, and before reaching the Montanvert they
have strewn their débris quite over the adjacent ice. A distinct limit
is thus formed between the clean Glacier du Géant and the other dirty
tributaries of the trunk-stream.
Now the eastern side of the Mer de Glace is observed on the whole to be
much more fiercely torn than the western side, and this excessive
crevassing has been referred to _the swifter motion of the Glacier du
Géant_. It has been thought that, like a powerful river, this glacier
drags its more sluggish neighbours after it, and thus tears them in the
manner observed. But the measurement of the foregoing three lines shows
that this cannot be the true cause of the crevassing. In each case the
stakes which moved quickest _lay upon the dirty portion of the
trunk-stream_, far to the east of the line of junction of the Glacier du
Géant, which in fact moved slowest of all.
[Sidenote: LAW OF MOTION SOUGHT.]
The general view of the glacier, and of the shape of the valley which it
filled, suggested to me that the analogy with a river might perhaps make
itself good beyond the limits hitherto contemplated. The valley was not
straight, but sinuous. At the Montanvert the convex side of the glacier
was turned eastward; at some distance higher up, near the passages
called _Les Ponts_, it was turned westward; and higher up again it was
turned once more, for a long stretch, eastward. Thus between Trélaporte
and the Ponts we had what is called a point of contrary flexure, and
between the Ponts and the Montanvert a second point of the same kind.
[Sidenote: CONJECTURE REGARDING CHANGE OF FLEXURE.]
Supposing a river, instead of the glacier, to sweep through this valley;
_its_ point of maximum motion would not always remain central, but would
deviate towards that side of the valley to which the river turned its
convex boundary. Indeed the positions of towns along the banks of a
navigable river are mainly determined by this circumstance. They are,
in most cases, situate on the convex sides of the bends, where the rush
of the water prevents silting up. Can it be then that the ice exhibits a
similar deportment? that the same principle which regulates the
distribution of people along the banks of the Thames is also acting with
silent energy amid the glaciers of the Alps? If this be the case, the
position of the point of maximum motion ought, of course, to shift with
the bending of the glacier. Opposite the Ponts, for example, the point
ought to be on the Glacier du Géant, and westward of the centre of the
trunk-stream; while, higher up, we ought to have another change to the
eastern side, in accordance with the change of flexure.
On the 25th of July a line was set out across the glacier, one of its
fixed termini being a mark upon the first of the three Ponts. The motion
of this line, measured on a subsequent day, and reduced to its daily
rate, was found to be as follows:--
Fourth Line.--Daily Motion.
No. of stake. Inches.
East 1 moved 6-1/2
2 " 8
3 " 12-1/2
4 " 15-1/4
5 " 15-1/2
6 " 18-3/4
7 " 18-1/4
8 " 18-3/4
9 " 19-1/2
10 moved 21
11 " 20-1/2
12 " 23-1/4
13 " 23-1/4
14 " 21
15 " 22-1/4
16 " 17-1/4
17 " 15 West.
This line, like the third, was set out and numbered from the eastern
side of the glacier, the theodolite occupying a position on the heights
of the Echelets. A moment's inspection of the table reveals a fact
different from that observed on the third line; _there_ the most
easterly stake moved with more than twice the velocity of the most
westerly one; _here_, on the contrary, the most westerly stake moves
with more than twice the velocity of the most easterly one.
To enable me to compare the motion of the eastern and western halves of
the glacier with greater strictness, my able and laborious companion
undertook the task of measuring with a surveyor's chain the line just
referred to; noting the pickets which had been fixed along the line, and
the other remarkable objects which it intersected. The difficulty of
thus directing a chain over crevasses and ridges can hardly be
appreciated except by those who have tried it. Nevertheless, the task
was accomplished, and the width of the Mer de Glace, at this portion of
its course, was found to be 863 yards, or almost exactly half a mile.
Referring to the last table, it will be seen that the two stakes
numbered 12 and 13 moved with a common velocity of 23-1/4 inches per
day, and that their motion is swifter than that of any of the others.
The point of swiftest motion may be taken midway between them, and this
point was found by measurement to lie 233 yards _west_ of the dirt which
marked the junction of the Glacier du Géant with its fellow tributaries:
whereas, in the former cases, it lay a considerable distance _east_ of
this limit. Its distance from the eastern side of the glacier was 601
yards, and from the western side 262 yards, being 170 yards west of the
centre of the glacier.
[Sidenote: CONJECTURE TESTED.]
But the measurements enabled me to take the stakes in pairs, and to
compare the velocity of a number of them which stood at certain
distances from the eastern side of the valley, with an equal number
which stood at the same distances from the western side. By thus
arranging the points two by two, I was able to compare the motion of the
entire body of the ice at the one side of the central line with that of
the ice at the other side. Stake 17 stood about as far from the western
side of the glacier as stake 3 did from its eastern side; 16 occupied
the same relation to 4; 15, to 5; 13, to 7; and 12, to 9.
Calling each pair of points which thus stand at equal distances from the
opposite sides _corresponding points_, the following little table
exhibits their comparative motions:--
Numbers and Velocities of Corresponding Points on the Fourth Line.
No. Vel. No. Vel. No. Vel. No. Vel. No. Vel.
West 17 15 16 17-1/4 15 22-1/4 13 23-1/4 12 23-1/4
East 3 12-1/2 4 15-1/4 5 15-1/2 7 18-1/4 9 19-1/2
[Sidenote: WESTERN HALF MOVES QUICKEST.]
The table explains itself. We see that while stake 17, which stands
_west_ of the centre, moves 15 inches, stake 3, which stands an equal
distance _east_ of the centre, moves only 12-1/2 inches. Comparing every
pair of the other points, we find the same to hold good; the western
stake moves in each case faster than the corresponding eastern one.
Hence, _the entire western half of the Mer de Glace, at the place
crossed by our fourth line, moves more quickly than the eastern half of
the glacier_.
We next proceeded farther up, and tested the contrary curvature of the
glacier, opposite to Trélaporte. The station chosen for this purpose was
on a grassy platform of the promontory, whence, on the 28th of July, a
row of stakes was fixed at right angles to the axis of the glacier.
Their motions, measured on the 31st, gave the following results:--
Fifth Line.[B]--Daily Motion.
No. of stake. Inches.
West 1 moved 11-1/4
2 " 13-1/2
3 " 12-3/4
4 " 15
5 " 15-1/4
6 " 16
7 " 17-1/4
8 " 19-1/4
9 moved 19-3/4
10 " 19
11 " 19-1/2
12 " 17-1/2
13 " 16
14 " 14-3/4
15 " 10 East.
This line was set out and numbered from the Trélaporte side of the
valley, and was also measured by Mr. Hirst, over boulders, ice-ridges,
chasms, and moraines. The entire width of the glacier here was found to
be 893 yards, or somewhat wider than it is at the Ponts. It will also be
observed that its motion is somewhat slower.
An inspection of the notes of this line showed me that stakes 3 and 14,
4 and 12, 7 and 10, were "corresponding points;" the first of each pair
standing as far from the western side, as the second stood from the
eastern. In the following table these points and their velocities are
arranged exactly as in the case of the fourth line.
Numbers and Velocities of the Corresponding Points on the Fifth Line.
No. Vel. No. Vel. No. Vel.
West 3 12-3/4 4 15 7 17-1/4
East 14 14-3/4 12 17-1/2 10 19
[Sidenote: EASTERN HALF MOVES QUICKEST.]
In each case we find that the stake on the eastern side moves more
quickly than the corresponding one upon the western side: so that where
the fifth line crosses the glacier _the eastern half of the Mer de Glace
moves more quickly than the western half_. This is the reverse of the
result obtained at our fourth line, but it agrees with that obtained on
our first three lines, where the curvature of the valley is similar. The
analogy between a river and a glacier moving through a sinuous valley is
therefore complete.
Supposing the points of maximum motion to be determined for a great
number of lines across the glacier, the line uniting all these points is
what mathematicians would call the _locus_ of the point of maximum
motion. At Trélaporte this line would lie east of the centre; at the
Ponts it would lie west of the centre; hence, in passing from Trélaporte
to the Ponts, it must cross the axis of the glacier. Again, at the
Montanvert, it would lie east of the centre, and between the Ponts and
the Montanvert the axis of the glacier would be crossed a second time.
Supposing the dotted line in Fig. 21 to represent the middle line of the
glacier, then the defined line would represent the locus of the point of
maximum motion. _It is a curve more deeply sinuous than the valley
itself, and it crosses the axis of the glacier at each point of contrary
flexure._
[Sidenote: LOCUS OF POINT OF SWIFTEST MOTION.]
[Illustration: Fig. 21. Locus of the Point of Maximum Motion.]
To complete our knowledge of the motion of the Mer de Glace, we
afterwards determined the velocity of its two accessible
tributaries--the Glacier du Géant, and the Glacier de Léchaud. On the
29th of July, a line of stakes was set out across the former, a little
above the Tacul, and their motion was subsequently found to be as
follows:
Sixth Line.--Daily Motion.
No. of stake. Inches.
1 moved 11
2 " 10
3 " 12
4 " 13
5 " 12
6 moved 12-3/4
7 " 10-1/2
8 " 10
9 " 9
10 " 5
The width of the glacier at this place we found to be 1134 yards, and
its maximum velocity, as shown by the foregoing table, 13 inches a day.
On the 1st of August a line was set out across the Glacier de Léchaud,
above its junction with the Talèfre: it commenced beneath the block of
stone known as the Pierre de Béranger. The displacements of the stakes,
measured on the 3rd of August, gave the following results:--
Seventh Line.--Daily Motion.
No. of stake. Inches.
1 moved 4-1/2
2 " 8-1/4
3 " 9-1/2
4 " 9
5 " 8-1/2
6 moved 7-1/2
7 " 6-1/4
8 " 8-1/2
9 " 7
10 " 5-1/2
The width of the Glacier de Léchaud at this place was found to be 825
yards; its maximum motion, as shown by the table, being 9-1/2 inches a
day. This is the slowest rate which we observed upon either the Mer de
Glace or its tributaries. The width of the Talèfre-branch, as it
descends the cascade, or, in other words, before it is influenced by the
pressure of the Léchaud, was found approximately to be 638 yards.
[Sidenote: SQUEEZING AT TRÉLAPORTE.]
The widths of the tributaries were determined for the purpose of
ascertaining the amount of lateral compression endured by the ice in its
passage through the neck of the valley at Trélaporte. Adding all
together we have--
Géant 1134 yards.
Léchaud 825 "
Talèfre 638 "
Total 2597 yards.
These three branches, as shown by the actual measurement of our 5th
line, are forced at Trélaporte through a channel 893 yards wide; the
width of the trunk stream is a little better than one-third of that of
its tributaries, and it passes through this gorge at a velocity of
nearly 20 inches a day.
[Sidenote: THE LÉCHAUD A DRIBLET.]
Limiting our view to one of the tributaries only, the result is still
more impressive. Previous to its junction with the Talèfre, the Glacier
de Léchaud stretches before the observer as a broad river of ice,
measuring 825 yards across: at Trélaporte it is squeezed, in a frozen
vice, between the Talèfre on one side and the Géant on the other, to a
driblet, measuring 85 yards in width, or about one-tenth of its former
transverse dimension. It will of course be understood that it is the
_form_ and not the _volume_ of the glacier that is affected to this
enormous extent by the pressure.
Supposing no waste took place, the Glacier de Léchaud would force
precisely the same amount of ice through the "narrows" at Trélaporte, in
one day, as it sends past the Pierre de Béranger. At the latter place
its velocity is about half of what it is at the former, but its width is
more than nine times as great. Hence, if no waste took place, its
_depth_, at Trélaporte, would be at _least_ 4-1/2 times its depth
opposite the Pierre de Béranger. Superficial and subglacial melting
greatly modify this result. Still I think it extremely probable that
observations directed to this end would prove the comparative
shallowness of the upper portions of the Glacier de Léchaud.
FOOTNOTES:
[A] Great care is necessary on the part of the man who measures the
displacements. The staff ought to be placed along the original line, and
the assistant ought to walk along it until the foot of a _perpendicular_
from the stake is attained. When several days' motion is to be measured,
this precaution is absolutely necessary; the eye being liable to be
grossly deceived in _guessing_ the direction of a perpendicular.
[B] The details of the measurement of the fourth and fifth lines are
published in the 'Philosophical Transactions,' vol. cxlix., p. 261.
ICE-WALL AT THE TACUL.
VELOCITIES OF TOP AND BOTTOM.
(11.)
As regards the motion of the _surface_ of a glacier, two laws are to be
borne in mind: 1st, that regarding the quicker movement of the centre;
2nd, that regarding the locus of the point of maximum motion. Our next
care must be to compare the motion of the surface of a glacier with the
motion of those parts which lie near its bed. Rendu first surmised that
the bottom of the glacier was retarded by friction, and both Professor
Forbes[A] and M. Martins[B] have confirmed the conjecture. Theirs are
the only observations which we possess upon the subject; and I was
particularly desirous to instruct myself upon this important head by
measurements of my own.
[Sidenote: FIRST ATTEMPT AT MEASUREMENT.]
During the summer of 1857 the eastern side of the Glacier du Géant, near
the Tacul, exposed a nearly vertical precipice of ice, measuring 140
feet from top to bottom. I requested Mr. Hirst to fix two stakes in the
same vertical plane, one at the top of the precipice and one near the
bottom. This he did upon the 3rd of August, and on the 5th I accompanied
him to measure the progress of the stakes. On the summit of the
precipice, and running along it, was the lateral moraine of the glacier.
The day was warm and the ice liquefying rapidly, so that the boulders
and débris, deprived incessantly of their support, came in frequent
leaps and rushes down the precipice. Into this peril my guide was about
to enter, to measure the displacement of the lower stake, while I was
to watch, and call out the direction in which he was to run when a stone
gave way. But I soon found that the initial motion was no sure index of
the final motion. By striking the precipice, the stones were often
deflected, and carried wide of their original direction. I therefore
stopped the man, and sent him to the summit of the precipice to remove
all the more dangerous blocks. This accomplished, he descended, and
while I stood beside him, executed the required measurement. From the
3rd to the 5th of August the upper stake had moved twelve inches, and
the lower one six.
Unfortunately some uncertainty attached itself to this result, due to
the difficulty of fixing the lower stake. The guide's attention had been
divided between his work and his safety, and he had to retreat more than
a dozen times from the falling boulders and débris. I, on the other
hand, was unwilling to accept an observation of such importance with a
shade of doubt attached to it. Hence arose the desire to measure the
motion myself. On the 11th of August I therefore reascended to the
Tacul, and fixed a stake at the top of the precipice, and another at the
bottom. While sitting on the old moraine looking at the two pickets, the
importance of determining the motion of a point midway between the top
and bottom forcibly occurred to me, but, on mentioning it to my guide,
he promptly pronounced any attempt of the kind absurd.
[Sidenote: STAKES FIXED AT TOP, BOTTOM, AND CENTRE.]
On scanning the place carefully, however, the value of the observation
appeared to me to outweigh the amount of danger. I therefore took my
axe, placed a stake and an auger against my breast, buttoned my coat
upon them, and cut an oblique staircase up the wall of ice, until I
reached a height of forty feet from the bottom. Here the position of the
stake being determined by Mr. Hirst, who was at the theodolite, I
pierced the ice with the auger, drove in the stake, and descended
without injury. During the whole operation however my guide growled
audibly.
On the following morning we commenced the ascent of Mont Blanc, a
narrative of which is given in Part I. We calculated on an absence of
three days, and estimated that the stakes which had just been fixed
would be ready for measurement on our return; but we did not reach
Chamouni until the afternoon of Friday, the 14th. Heavy clouds settled,
during our descent, upon the summits behind us, and a thunder-peal from
the Aiguilles soon heralded a fall of rain, which continued without
intermission till the afternoon of the 16th, when the atmosphere
cleared, and showed the mountains clothed to their girdles with snow.
The Montanvert was thickly covered, and on our way to it we met the
servants in charge of the cattle, which had been driven below the
snow-line to obtain food.
[Sidenote: THROUGH GLOOM TO THE TACUL.]
On Monday morning, the 17th, a dense fog filled the valley of the Mer de
Glace. I watched it anxiously. The stakes which we had set at the Tacul
had been often in my thoughts, and I wished to make some effort to save
the labour and peril incurred in setting them from being lost. I
therefore set out, in one of the clear intervals, accompanied by my
friend and Simond, determined to measure the motion of the stakes, if
possible, or to fix them more firmly, if they still stood. As we passed,
however, from l'Angle to the glacier, the fog became so dense and
blinding that we halted. At my request Mr. Hirst returned to the
Montanvert; and Simond, leaving the theodolite in the shelter of a rock,
accompanied me through the obscurity to the Tacul. We found the topmost
stake still stuck by its point in the ice; but the two others had
disappeared, and we afterwards discovered their fragments in a
snow-buttress, which reared itself against the base of the precipice.
They had been hit by the falling stones, and crushed to pieces. Having
thus learned the worst, we descended to the Montanvert amid drenching
rain.
[Sidenote: DESCENT OF BOULDERS.]
On the morning of the 18th there was no cloud to be seen anywhere, and
the sunlight glistened brightly on the surface of the ice. We ascended
to the Tacul. The spontaneous falling of the stones appeared more
frequent this morning than I had ever seen it. The sun shone with
unmitigated power upon the ice, producing copious liquefaction. The
rustle of falling débris was incessant, and at frequent intervals the
boulders leaped down the precipice, and rattled with startling energy
amid the rocks at its base. I sent Simond to the top to remove the
looser stones; he soon appeared, and urged the moraine-shingle in
showers down the precipice, upon a bevelled slope of which some blocks
long continued to rest. They were out of the reach of the guide's bâton,
and he sought to dislodge them by sending other stones down upon them.
Some of them soon gave way, drawing a train of smaller shingle after
them; others required to be hit many times before they yielded, and
others refused to be dislodged at all. I then cut my way up the
precipice in the manner already described, fixed the stake, and
descended as speedily as possible. We afterwards fixed the bottom stake,
and on the 20th the displacements of all three were measured.[C] The
spaces passed over by the respective stakes in 24 hours were found to be
as follows:--
Inches.
Top stake 6.00
Middle stake 4.50
Bottom stake 2.56
[Sidenote: MOTION OF STAKES.]
The height of the precipice was 140.8 feet, but it sloped off at its
upper portion. The height of the middle stake above the ground was 35
feet, and of the bottom one 4 feet. It is therefore proved by these
measurements that the bottom of the ice-wall at the Tacul moves with
less than half the velocity of the top; while the displacement of the
intermediate stake shows how the velocity gradually increases from the
bottom upwards.
FOOTNOTES:
[A] 'Edinb. Phil. Journ.,' Oct. 1846, p. 417.
[B] Agassiz, 'Système Glaciaire,' p. 522.
[C] On this latter occasion my guide volunteered to cut the steps for me
up to the pickets; and I permitted him to do so. In fact, he was at
least as anxious as myself to see the measurement carried out.
WINTER MOTION OF THE MER DE GLACE.
(12.)
The winter measurements were executed in the manner already described,
on the 28th and 29th of December, 1859. The theodolite was placed on the
mountain's side flanking the glacier, and a well-defined object was
chosen at the opposite side of the valley, so that a straight line
between this object and the theodolite was approximately perpendicular
to the axis of the glacier. Fixing the telescope in the first instance
with its cross hairs upon the object, its end was lowered until it
struck the point upon the glacier at which a stake was to be fixed.
Thanks to the intelligence of my assistants, after the fixing of the
first stake they speedily took up the line at all other points,
requiring very little correction to make their positions perfectly
accurate. On the day following that on which the stakes were driven in,
the theodolite was placed in the same position, and the distances to
which the stakes had moved from their original positions were accurately
determined. As already stated, the first line crossed the glacier about
80 yards above the Montanvert Hotel.
[Sidenote: HALF OF SUMMER MOTION.]
Line No. I.--Winter Motion in Twenty-four Hours.
No. of stake. Inches.
West 1 7-1/4
2 11
3 13-1/2
4 13
5 13-3/4
6 14-1/4
7 15-3/4
8 15-3/4
9 12-1/4
10 12
11 6-1/2 East.
[Sidenote: THE SAME LAW IN SUMMER AND WINTER.]
The maximum here is fifteen and three-quarters inches; the maximum
summer motion of the same portion of the glacier is about thirty
inches. These measurements also show that in winter, as well as in
summer, the side of the glacier opposite to the Montanvert moves quicker
than that adjacent to it. The stake which moved with the maximum
velocity was beyond the moraine of La Noire. The second line crossed the
glacier about 130 yards below the Montanvert.
Line No. II.--Winter Motion in Twenty-four Hours.
No. of stake. Inches.
1 7-3/4
2 9-1/2
3 13-3/4
4 16
5 16
6 15-3/4
7 17-1/2
8 16-1/2
9 14-1/2
10 14
The maximum here is an inch and three-quarters greater than that of line
No. 1. The summer maximum at this portion of the glacier also exceeds
that of the part intersected by line No. 1. The surface of the glacier
between the two lines is in a state of tension which relieves itself by
a system of transverse fissures, and thus permits of the quicker advance
of the forward portion.
My desire, in making these measurements, was, in the first place, to
raise the winter observations of the motion to the same degree of
accuracy as that already possessed by the summer ones. Auguste Balmat
had already made a series of winter observations on the Mer de Glace;
but they were made in the way employed before the introduction of the
theodolite by Agassiz and Forbes, and shared the unavoidable roughness
of such a mode of measurement. They moreover gave us no information as
to the motion of the different parts of the glacier along the same
transverse line, and this, for reasons which will appear subsequently,
was the point of chief interest to me.
CAUSE OF GLACIER-MOTION.
DE SAUSSURE'S THEORY.
(13.)
Perhaps the first attempt at forming a glacier-theory is that of
Scheuchzer in 1705. He supposed the motion to be caused by the
conversion of water into ice within the glacier; the known and almost
irresistible expansion which takes place on freezing, furnishing the
force which pushed the glacier downward. This idea was illustrated and
developed with so much skill by M. de Charpentier, that his name has
been associated with it; and it is commonly known as the Theory of
Charpentier, or the Dilatation-Theory. M. Agassiz supported this theory
for a time, but his own thermometric experiments show us that the body
of the glacier is at a temperature of 32° Fahr.; that consequently there
is no interior magazine of cold to freeze the water with which the
glacier is supposed to be incessantly saturated. So that these
experiments alone, if no other grounds existed, would prove the
insufficiency of the theory of dilatation. I may however add, that the
arguments most frequently urged against this theory deal with an
assumption, which I do not think its author ever intended to make.
[Sidenote: THE GLACIER SLIDES.]
Another early surmise was that of Altmann and Grüner (1760), both of
whom conjectured that the glacier slid along its bed. This theory
received distinct expression from De Saussure in 1799; and has since
been associated with the name of that great alpine traveller, being
usually called the 'Theory of Saussure,' and sometimes the 'Sliding
Theory.' It is briefly stated in these words:--
"Almost every glacier reposes upon an inclined bed, and those of any
considerable size have beneath them, even in winter, currents of water
which flow between the ice and the bed which supports it. It may
therefore be understood that these frozen masses, drawn down the slope
on which they repose, disengaged by the water from all adhesion to the
bottom, sometimes even raised by this water, must glide by little and
little, and descend, following the inclinations of the valleys, or of
the slopes which they cover. It is this slow but continual sliding of
the ice on its inclined base which carries it into the lower
valleys."[A]
[Sidenote: STRAINED INTERPRETATION.]
De Saussure devoted but little time to the subject of glacier-motion;
and the absence of completeness in the statement of his views, arising
no doubt from this cause, has given subsequent writers occasion to affix
what I cannot help thinking a strained interpretation to the sliding
theory. It is alleged that he regarded a glacier as a perfectly rigid
body; that he considered it to be "a mass of ice of small depth, and
considerable but uniform breadth, sliding down a uniform valley, or
pouring from a narrow valley into a wider one."[B] The introduction "of
the smallest flexibility or plasticity" is moreover emphatically denied
to him.[C]
It is by no means probable that the great author of the 'Voyages' would
have subscribed to this "rigid" annotation. His theory, be it
remembered, is to some extent _true_: the glacier moves over its bed in
the manner supposed, and the rocks of Britain bear to this day the
traces of these mighty sliders. De Saussure probably contented himself
with a general statement of what he believed to be the substantial
cause of the motion. He visited the Jardin, and saw the tributaries of
the Mer de Glace turning round corners, welding themselves together, and
afterwards moving through a sinuous trunk-valley; and it is scarcely
credible that in the presence of such facts he would have denied all
flexibility to the glacier.
The statement that he regarded a glacier to be a mass of ice of uniform
width, is moreover plainly inconsistent with the following description
of the glacier of Mont Dolent: "Its most elevated plateau is a great
circus, surrounded by high cliffs of granite, of pyramidal forms; thence
the glacier descends through a gorge, in which _it is narrowed_; but
after having passed the gorge, it _enlarges again_, spreading out like a
fan. Thus it has on the whole the form of a sheaf tied in the middle and
dilated at its two extremities."[D]
[Sidenote: GLACIER OF MONT DOLENT.]
Curiously enough this very glacier, and these very words, are selected
by M. Rendu as illustrative of the plasticity of glaciers. "Nothing," he
says, "shows better the extent to which a glacier moulds itself to its
locality than the form of the glacier of Mont Dolent in the Valley of
Ferret;" and he adds, in connexion with the same passage, these
remarkable words:--"There is a multitude of facts which would seem to
necessitate the belief that the substance of glaciers enjoys a kind of
ductility which permits it to mould itself to the locality which it
occupies, to grow thin, to swell, and to narrow itself like a soft
paste."[E]
FOOTNOTES:
[A] 'Voyages,' § 535.
[B] James D. Forbes, 'Occasional Papers on the Theory of Glaciers,'
1859, p. 100.
[C] "I adhere to the definition as excluding the introduction of the
smallest flexibility or plasticity." 'Occ. Pap.,' p. 96.
[D] 'Voyages,' tome ii. p. 290.
[E] In connexion with this brief sketch of the 'Sliding Theory,' it
ought to be stated, that Mr. Hopkins has proved experimentally, that ice
may descend an incline at a sensibly uniform rate, and that the velocity
is augmented by increasing the weight. In this remarkable experiment the
motion was due to the slow disintegration of the lower surface of the
ice. See 'Phil. Mag.,' 1845, vol. 26.
RENDU'S THEORY.
(14.)
[Sidenote: RENDU'S CHARACTER.]
M. Rendu, Bishop of Annecy, to whose writings I have just referred, died
last autumn.[A] He was a man of great repute in his diocese, and we owe
to him one of the most remarkable essays upon glaciers that have ever
appeared. His knowledge was extensive, his reasoning close and accurate,
and his faculty of observation extraordinary. With these were associated
that intuitive power, that presentiment concerning things as yet
untouched by experiment, which belong only to the higher class of minds.
Throughout his essay a constant effort after quantitative accuracy
reveals itself. He collects observations, makes experiments, and tries
to obtain numerical results; always taking care, however, so to state
his premises and qualify his conclusions that nobody shall be led to
ascribe to his numbers a greater accuracy than they merit. It is
impossible to read his work, and not feel that he was a man of
essentially truthful mind, and that science missed an ornament when he
was appropriated by the Church.
The essay above referred to is printed in the tenth volume of the
Memoirs of the Royal Academy of Sciences of Savoy, published in 1841,
and is entitled, '_Théorie des Glaciers de la Savoie, par M. le Chanoine
Rendu, Chevalier du Mérite Civil et Secrétaire perpétuel_.' The paper
had been written for nearly two years, and might have remained
unprinted, had not another publication on the same subject called it
forth.
I will place a few of the leading points of this remarkable production
before the reader; commencing with a generalization which is highly
suggestive of the character of the author's mind.
[Sidenote: "THEORIE DES GLACIERS DE LA SAVOIE."]
He reflects on the accumulation of the mountain-snows, each year adding
fifty-eight inches of ice to a glacier. This would make Mont Blanc four
hundred feet higher in a century, and four thousand feet higher in a
thousand years. "It is evident," he says, "that nothing like this occurs
in nature." The escape of the ice then leads him to make some general
remarks on what he calls the "law of circulation." "The conserving will
of the Creator has employed for the permanence of His work the great law
of _circulation_, which, strictly examined, is found to reproduce itself
in all parts of nature. The waters circulate from the ocean to the air,
from the air to the earth, and from the earth to the ocean.... The
elements of organic substances circulate, passing from the solid to the
liquid or aëriform condition, and thence again to the state of solidity
or of organisation. That universal agent which we designate by the names
of fire, light, electricity, and magnetism, has probably also a
_circulation_ as wide as the universe." The italics here are Rendu's
own. This was published in 1841, but written, we are informed, nearly
two years before. In 1842 Mr. Grove wrote thus:--"Light, heat,
magnetism, motion, and chemical affinity, are all convertible material
affections." More recently Helmholtz, speaking of the "circuit" formed
by "heat, light, electricity, magnetism, and chemical affinity," writes
thus:--"Starting from each of these different manifestations of natural
forces, we can set every other in action." I quote these passages
because they refer to the same agents as those named by M. Rendu, and to
which he ascribes "_circulation_." Can it be doubted that this Savoyard
priest had a premonition of the Conservation of Force? I do not want to
lay more stress than it deserves upon a conjecture of this kind; but
its harmony with an essay remarkable for its originality gives it a
significance which, if isolated, it might not possess.
[Sidenote: GLACIERS RIGHTLY DIVIDED.]
With regard to the glaciers, Rendu commences by dividing them into two
kinds, or rather the selfsame glacier into two parts, one of which he
calls the "_glacier réservoir_," the other the "_glacier
d'écoulement_,"--two terms highly suggestive of the physical
relationship of the _névé_ and the glacier proper. He feeds the
reservoirs from three sources, the principal one of which is the snow,
to which he adds the rain, and the vapours which are condensed upon the
heights without passing into the state of either rain or snow. The
conversion of the snow into ice he supposes to be effected by four
different causes, the most efficacious of which is _pressure_.[B] It is
needless to remark that this quite agrees with the views now generally
entertained.
In page 60 of the volume referred to there is a passage which shows that
the "veined structure" of the glacier had not escaped him, though it
would seem that he ascribed it to stratification. "When," he writes, "we
perceive the profile of a glacier on the walls of a crevasse, we see
different layers distinct in colour, but more particularly in density;
some seem to have the hardness, as they have the greenish colour, of
glass; others preserve the whiteness and porosity of the snow." There is
also a very close resemblance between his views of the influence of
"time and cohesion" and those of Prof. Forbes. "We may conclude," he
writes, "that _time_, favouring the action of _affinity_, and the
pressure of the layers one upon the other, causes the little crystals of
which snow is composed to approach each other, bring them into contact,
and convert them into ice."[C] Regelation also appears to have attracted
his notice.[D] "When we fill an ice-house," he writes, "we break the ice
into very small fragments; afterwards we wet it with water 8 or 10
degrees above zero (Cent.) in temperature; but, notwithstanding this,
the whole is converted into a compact mass of ice." He moreover
maintains, in almost the same language as Prof. Forbes,[E] the opinion,
that ice has always an inner temperature lower than zero (Cent.). He
believed this to be a property "inherent to ice." "Never," he says, "can
a calorific ray pass the first surface of ice to raise the temperature
of the interior."[F]
[Sidenote: OBSERVATIONS AND HYPOTHESES.]
He notices the direction of the glacier as influencing the wasting of
its ridges by the sun's heat; ascribing to it the effect to which I have
referred in explaining the wave-like forms upon the surface of the Mer
de Glace. His explanation of the Moulins, too, though insufficient,
assigns a true cause, and is an excellent specimen of physical
reasoning.
With regard to the diminution of the _glaciers réservoirs_, or, in other
words, to the manner in which the ice disappears, notwithstanding the
continual additions made to it, we have the following remarkable
passage:--"In seeking the cause of the diminution of glaciers, it has
occurred to my mind that the ice, notwithstanding its hardness and its
rigidity, can only support a given pressure without breaking or being
squeezed out. According to this supposition, whenever the pressure
exceeds that force, there will be rupture of the ice, and a flow in
consequence. Let us take, at the summit of Mont Blanc, a column of ice
reposing on a horizontal base. The ice which forms the first layer of
that column is compressed by the weight of all the layers above it; but
if the solidity of the said first layer can only support a weight equal
to 100, when the weight exceeds this amount there will be rupture and
spreading out of the ice of the base. Now, something very similar occurs
in the immense crust of ice which covers the summits of Mont Blanc. This
crust appears to augment at the upper surface and to diminish by the
sides. To assure oneself that the movement is due to the force of
pressure, it would be necessary to make a series of experiments upon the
solidity of ice, such as have not yet been attempted."[G] I may remark
that such experiments substantially verify M. Rendu's notion.
But it is his observations and reasoning upon the _glaciers
d'écoulement_ that chiefly interest us. The passages in his writings
where he insists upon the power of the glaciers to mould themselves to
their localities, and compares them to a soft paste, to lava at once
ductile and liquid, are well known from the frequent and flattering
references of Professor Forbes; but there are others of much greater
importance, which have hitherto remained unknown in this country.
Regarding the motion of the Mer de Glace, Rendu writes as follows:--
[Sidenote: MEASUREMENT OF MOTION.]
[Sidenote: THE SIDES OF THE GLACIER RETARDED.]
"I sought to appreciate the quantity of its motion; but I could only
collect rather vague data. I questioned my guides regarding the position
of an enormous rock at the edge of the glacier, but still upon the ice,
and consequently partaking of its motion. The guides showed me the place
where it stood the preceding year, and where it had stood two, three,
four, and five years previously; they showed me the place where it would
be found in a year, in two years, &c.; _so certain are they of the
regularity of the motion_. Their reports, however, did not always agree
precisely with each other, and their indications of time and distance
lack the precision without which we proceed obscurely in the physical
sciences. In reducing these different indications to a mean, I found the
total advance of the glacier to be about 40 feet a year. During my last
journey I obtained more certain data, which I have stated in the
preceding chapter. _The enormous difference between the two results
arises from the fact that the latter observations were made at the
centre of the glacier_, WHICH MOVES MORE RAPIDLY, _while the former were
made at the side, where the ice_ IS RETAINED BY THE FRICTION AGAINST ITS
ROCKY WALLS."[H]
An opinion, founded on a grave misapprehension which Rendu enables us to
correct, is now prevalent in this country, not only among the general
public, but also among those of the first rank in science. The nature of
the mistake will be immediately apparent. At page 128 of the 'Travels in
the Alps' its distinguished author gives a sketch of the state of our
knowledge of glacier-motion previous to the commencement of his
inquiries. He cites Ebel, Hugi, Agassiz, Bakewell, De la Beche,
Shirwell, Rendu, and places them in open contradiction to each other.
Rendu, he says, gives the motion of the Mer de Glace to be "242 feet per
annum; 442 feet per annum; a foot a day; 400 feet per annum, and 40 feet
per annum, or _one-tenth_ of the last!" ... and he adds, "I was not
therefore wrong in supposing that the actual progress of a glacier was
yet a new problem when I commenced my observations on the Mer de Glace
in 1842."[I]
In the 'North British Review' for August, 1859, a writer equally
celebrated for the brilliancy of his discoveries and the vigour of his
pen, collected the data furnished by the above paragraph into a table,
which he introduced to his readers in the following words:--"It is to
Professor Forbes alone that we owe the first and most correct researches
respecting the motion of glaciers; and in proof of this, we have only to
give the following list of observations which had been previously made.
Observers. Name of glacier. Annual rate of motion.
Ebel Chamouni 14 feet
Ebel Grindelwald 25 "
Hugi Aar 240 "
Agassiz Aar 200 "
Bakewell Mer de Glace 540 "
De la Beche Mer de Glace 600 "
Shirwell Mer de Glace 300 "
M. Rendu Mer de Glace 365 "
Saussure's Ladder Mer de Glace 375 "
... Such was the state of our knowledge when Professor Forbes undertook
the investigation of the subject."
I am persuaded that the writer of this article will be the first to
applaud any attempt to remove an error which, advanced on his great
authority, must necessarily be widely disseminated. The numbers in the
above table certainly differ widely, and it is perhaps natural to
conclude that such discordant results can be of no value; but the fact
really is that _every one of them may be perfectly correct_. This fact,
though overlooked by Professor Forbes, was clearly seen by Rendu, who
pointed out with perfect distinctness the sources from which the
discrepancies were derived.
[Sidenote: DISCREPANCIES EXPLAINED.]
"It is easy," he says, "to comprehend that it is impossible to obtain a
general measure,--that there ought to be one for each particular
glacier. The nature of the slope, the number of changes to which it is
subjected, the depth of the ice, the width of the couloir, the form of
its sides, and a thousand other circumstances, must produce variations
in the velocity of the glacier, and these circumstances cannot be
everywhere absolutely the same. Much more, it is not easy to obtain this
velocity for a single glacier, and for this reason. In those portions
where the inclination is steep, the layer of ice is thin, and its
velocity is great; in those where the slope is almost nothing, the
glacier swells and accumulates; the mass in motion being double, triple,
&c., the motion is only the half, the third, &c.
[Sidenote: LIQUID MOTION ASCRIBED TO GLACIER.]
"But this is not all," adds M. Rendu: "_Between the Mer de Glace and a
river, there is a resemblance so complete that it is impossible to find
in the latter a circumstance which does not exist in the former._ In
currents of water the motion is not uniform, neither throughout their
width nor throughout their depth; _the friction of the bottom, that of
the sides_, the action of obstacles, cause the motion to vary, _and only
towards the middle of the surface is this entire...._"[J]
In 1845 Professor Forbes appears to have come to the same conclusion as
M. Rendu; for after it had been proved that the centre of the Aar
glacier moved quicker than the side in the ratio of fourteen to one, he
accepted the result in these words:--"The movement of the centre of the
glacier is to that of a point five mètres from the edge as FOURTEEN to
ONE: such is the effect of plasticity!"[K] Indeed, if the differences
exhibited in the table were a proof of error, the observations of
Professor Forbes himself would fare very ill. The measurements of
glacier-motion made with his own hands vary from less than 42 feet a
year to 848 feet a year, the minimum being less than _one-twentieth_ of
the maximum; and if we include the observations made by Balmat, the
fidelity of which has been certified by Professor Forbes, the minimum is
only _one-thirty-seventh_ of the maximum.
[Sidenote: NORTH BRITISH REVIEW.]
There is another point connected with Rendu's theory which needs
clearing up:--"The idea," writes the eminent reviewer, "that a glacier
is a semifluid body is no doubt startling, especially to those who have
seen the apparently rigid ice of which it is composed. M. Rendu himself
shrank from the idea, and did not scruple to say that 'the rigidity of a
mass of ice was in direct opposition to it;' and we think that Professor
Forbes himself must have stood aghast when his fancy first associated
the notion of imperfect fluidity with the solid or even the fissured ice
of the glacier, and when he saw in his mind's eye the glaciers of the
Alps flowing like a river along their rugged bed. A truth like this was
above the comprehension and beyond the sympathy of the age; and it
required a moral power of no common intensity to submit it to the ordeal
of a shallow philosophy, and the sneers of a presumptuous criticism."
These are strong words; but the fact is that, so far from "shrinking"
from the idea, Rendu affirmed, with a clearness and an emphasis which
have not been exceeded since, that all the phenomena of a river were
reproduced upon the Mer de Glace; its deeps, its shallows, its
widenings, its narrowings, its rapids, its places of slow motion, and
the quicker flow of its centre than of its sides. He did not shrink from
accepting a difference between the central and lateral motion amounting
to a ratio of ten to one--a ratio so large that Professor Forbes at one
time regarded the acceptance of it as a simple absurdity. In this he was
perhaps justified; for his own first observations, which, however
valuable, were hasty and incomplete, gave him a maximum ratio of about
one and a half to one, while the ratio in some cases was nearly one of
_equality_. The observations of Agassiz however show that the ratio,
instead of being ten to one, may be _infinity_ to one; for the lateral
ice may be so held back by a local obstacle that in the course of a year
it shall make no sensible advance at all.
[Sidenote: THE ICE AND THE GLACIER.]
From one thing only did M. Rendu shrink; and it is _the_ thing regarding
which we are still disunited. He shrank from stating the physical
quality of the ice in virtue of which a glacier moved like a river. He
demands experiments upon snow and ice to elucidate this subject. The
very observations which Professor Forbes regards as proofs are those of
which we require the physical explanation. It is not the viscous flow,
if you please to call it such, of the glacier as a whole that here
concerns us; but it is the quality of the _ice_ in virtue of which this
kind of motion is accomplished. Professor Forbes sees this difference
clearly enough: he speaks of "fissured ice" being "flexible" in hand
specimens; he compares the glacier to a mixture of ice and sand; and
finally, in a more matured paper, falls back for an explanation upon the
observations of Agassiz regarding the capillaries of the glacier.[L]
FOOTNOTES:
[A] Expressions such as "last summer," "last autumn," "recently," will
be taken throughout in the sense which they had in the early half of
1860, when this book was first published.--L. C. T.
[B] 'Memoir,' p. 77.
[C] P. 75.
[D] P. 71.
[E] 'Philosophical Magazine,' 1859.
[F] 'Memoir,' p. 69.
[G] Page 80.
[H] Page 95.
[I] At page 38 of the 'Travels' the following passage also occurs:--"I
believe that I may safely affirm that not one observation of the rate of
motion of a glacier, either on the average or at any particular season
of the year, existed when I commenced my experiments in 1842."
[J] 'Théorie,' p. 96.
[K] 'Occ. Pap.,' p. 74.
[L] In all that has been written upon glaciers in this country the above
passages from the writings of Rendu are unquoted; and many who mingled
very warmly in the discussions of the subject were, until quite
recently, ignorant of their existence. I was long in this condition
myself, for I never supposed that passages which bear so directly upon a
point so much discussed, and of such cardinal import, could have been
overlooked; or that the task of calling attention to them should devolve
upon myself nearly twenty years after their publication. Now that they
are discovered, I conceive no difference of opinion can exist as to the
propriety of placing them in their true position.
(15.)
The measurements of Agassiz and Forbes completely verify the
anticipations of Rendu; but no writer with whom I am acquainted has
added anything essential to the Bishop's statements as to the identity
of glacier and liquid motion. He laid down the conditions of the problem
with perfect clearness, and, as regards the distribution of merit, the
point to be decided is the relative importance of his idea, and of the
measurements which were subsequently made.
[Sidenote: OBSERVATIONS OF FORBES.]
The observations on which Professor Forbes based the analogy between a
glacier and a river are the following:--In 1842 he fixed four marks upon
the Mer de Glace a little below the Montanvert, the first of which was
100 yards distant from the side of the glacier, while the last was at
the centre "or a little beyond it." The relative velocity of these four
points was found to be
1.000 1.332 1.356 1.367.
The first observations were made upon two of these points, two others
being subsequently added. Professor Forbes also determined the velocity
of two points on the Glacier du Géant, and found the ratio of motion, in
the first instance, to be as 14 to 32. Subsequent measurements, however,
showed the ratio to be as 14 to 18, the larger motion belonging to the
station nearest to the centre of the glacier. These are the only
measurements which I can find in his large work that establish the
swifter motion of the centre of the glacier; and in these cases the
velocity of the centre is compared with that of _one side_ only. In no
instance that I am aware of, either in 1842 or subsequent years, did
Professor Forbes extend his measurements quite across a glacier; and as
regards completeness in this respect, no observations hitherto made can
at all compare with those executed at the instance of Agassiz upon the
glacier of the Aar.
In 1844 Professor Forbes made a series of interesting experiments on a
portion of the Mer de Glace near l'Angle. He divided a length of 90 feet
into 45 equal spaces, and fixed pins at the end of each. His theodolite
was placed upon the ice, and in seventeen days he found that the ice 90
feet nearer the centre than the theodolite had moved 26 inches past the
latter. These measurements were undertaken for a special object, and
completely answered the end for which they were intended.
In 1846 Professor Forbes made another important observation. Fixing
three stakes at the heights of 8, 54, and 143 feet above the bed of the
glacier, he found that in five days they moved respectively 2.87, 4.18,
and 4.66 feet. The stake nearest the bed moved most slowly, thus
showing that the ice is retarded by friction. This result was
subsequently verified by the measurements of M. Martins, and by my own.
If we add to the above an observation made during a short visit to the
Aletsch glacier in 1844, which showed its lateral retardation, I believe
we have before us the whole of the measurements executed by Professor
Forbes, which show the analogy between the motion of a glacier and that
of a viscous body.
[Sidenote: MEASUREMENTS OF AGASSIZ.]
Illustrative of the same point, we have the elaborate and extensive
series of measurements executed by M. Wild under the direction of M.
Agassiz upon the glacier of the Aar in 1842, 1843, 1844, and 1845, which
exhibit on a grand scale, and in the most conclusive manner, the
character of the motion of this glacier; and also show, on close
examination, an analogy with fluid motion which neither M. Agassiz nor
Professor Forbes suspected. The former philosopher publishes a section
in his 'Système Glaciaire,' entitled 'Migrations of the Centre;' in
which he shows that the middle of the glacier is not always the point of
swiftest motion. The detection of this fact demonstrates the attention
devoted by M. Agassiz to the discussion of his observations, but he
gives no clue to the cause of the variation. On inspecting the shape of
the valley through which the Aar glacier moves, I find that these
"migrations" follow the law established in 1857 upon the Mer de Glace,
and enunciated at page 286.
To sum up this part of the question:--The _idea_ of semi-fluid motion
belongs entirely to Rendu; the _proof_ of the quicker central flow
belongs in part to Rendu, but almost wholly to Agassiz and Forbes; the
proof of the retardation of the bed belongs to Forbes alone; while the
discovery of the locus of the point of maximum motion belongs, I
suppose, to me.
FORBES'S THEORY.
(16.)
The formal statement of this theory is given in the following words:--"A
glacier is an imperfect fluid, or viscous body, which is urged down
slopes of a certain inclination by the mutual pressure of its parts."
The consistency of the glacier is illustrated by reference to treacle,
honey, and tar, and the theory thus enunciated and exemplified is called
the 'Viscous Theory.'
It has been the subject of much discussion, and great differences of
opinion are still entertained regarding it. Able and sincere men take
opposite sides; and the extraordinary number of Reviews which have
appeared upon the subject during the last two years show the interest
which the intellectual public of England take in the question. The chief
differences of opinion turn upon the inquiry as to what Professor Forbes
really meant when he propounded the viscous theory; some affirm one
thing, some another, and, singularly enough, these differences continue,
though the author of the theory has at various times published
expositions of his views.
[Sidenote: "FACTS AND PRINCIPLES."]
The differences referred to arise from the circumstances that a
sufficient distinction has not been observed between _facts_ and
_principles_, and that the viscous theory has assumed various forms
since its first promulgation. It has been stated to me that the theory
of Professor Forbes is "the congeries of facts" which he has discovered.
But it is quite evident that no recognition, however ample, of these
facts would be altogether satisfactory to Professor Forbes himself. He
claims recognition of his _theory_,[A] and no writer with whom I am
acquainted makes such frequent use of the term. What then can the
viscous theory mean apart from the facts? I interpret it as furnishing
the principle from which the facts follow as physical consequences--that
the glacier moves as a river because the ice is viscous. In this sense
only can Professor Forbes's views be called a theory; in any other, his
experiments are mere illustrations of the facts of glacier motion, which
do not carry us a hair's breadth towards their physical cause.
[Sidenote: VISCOUS THEORY;--WHAT IS IT?]
What then is the meaning of viscosity or viscidity? I have heard it
defined by men of high culture as "gluey tenacity;" and such tenacity
they once supposed a glacier to possess. If we dip a spoon into treacle,
honey, or tar, we can draw the substance out into filaments, and the
same may be done with melted caoutchouc or lava. All these substances
are viscous, and all of them have been chosen to illustrate the physical
property in virtue of which a glacier moves. Viscosity then consists in
the power of being drawn out when subjected to a force of tension, the
substance, after stretching, being in a state of molecular equilibrium,
or, in other words, devoid of that elasticity which would restore it to
its original form. This certainly was the idea attached to Professor
Forbes's words by some of his most strenuous supporters, and also by
eminent men who have never taken part in any controversy on the subject.
Mr. Darwin, for example, speaks of felspathic rocks being "stretched"
while flowing slowly onwards in a pasty condition, in precisely the same
manner as Professor Forbes believes that the ice of moving glaciers is
stretched and fissured; and Professor Forbes himself quotes these words
of Mr. Darwin as illustrative of his theory.[B]
The question now before us is,--Does a glacier exhibit that power of
yielding to a force of tension which would entitle its ice to be
regarded as a viscous substance?
[Sidenote: THEORY TESTED.]
With a view to the solution of this question Mr. Hirst took for me the
inclinations of the Mer de Glace and all its tributaries in 1857; the
effect of a change of inclination being always noted. I will select from
those measurements a few which bear more specially upon the subject now
under consideration, commencing with the Glacier des Bois, down which
the ice moves in that state of wild dislocation already described. The
inclination of the glacier above this cascade is 5° 10', and that of the
cascade itself is 22° 20', the change of inclination being therefore 17°
10'.
[Illustration: Fig. 22. Inclinations of ice cascasde of the Glacier des
Bois.]
In Fig. 22 I have protracted the inclination of the cascade and of the
glacier above it; the line A B representing the former and B C the
latter. Now a stream of molten lava, of treacle, or tar, would, in
virtue of its viscosity, be able to flow over the brow at B without
breaking across; but this is not the case with the glacier; it is so
smashed and riven in crossing this brow, that, to use the words of
Professor Forbes himself, "it pours into the valley beneath in a cascade
of icy fragments."
[Sidenote: INCLINATIONS OF THE MER DE GLACE.]
But this reasoning will appear much stronger when we revert to other
slopes upon the Mer de Glace. For example, its inclination above l'Angle
is 4°, and it afterwards descends a slope of 9° 25', the change of
inclination being 5° 25'. If we protract these inclinations to scale, we
have the line A B, Fig. 23, representing the steeper slope, and B C
that of the glacier above it. One would surely think that a viscous body
could cross the brow B without transverse fracture, but this the glacier
cannot do, and Professor Forbes himself pronounces this portion of the
Mer de Glace impassable. Indeed it was the profound crevasses here
formed which placed me in a difficulty already referred to. Higher up
again, the glacier is broken on passing from a slope of 3° 10' to one of
5°. Such observations show how differently constituted a glacier is from
a stream of lava in a "pasty condition," or of treacle, honey, tar, or
melted caoutchouc, to all which it has been compared. In the next
section I shall endeavour to explain the origin of the crevasses, and
shall afterwards make a few additional remarks on the alleged viscosity
of ice.
[Illustration: Fig. 23. Inclinations of Mer de Glace above l'Angle.]
FOOTNOTES:
[A] "Mr. Hopkins," writes Professor Forbes, "has done me the honour, in
the memoirs before alluded to, to mention with approbation my
observations and experiments on the subject of glaciers. He has been
more sparing either in praise or criticism of the theory which I have
founded upon them. Had Mr. Hopkins," &c.--_Eighth Letter_; 'Occ.
Papers,' p. 66.
[B] 'Occ. Papers,' p. 92.
THE CREVASSES.
(17.)
[Sidenote: CREVASSES CAUSED BY THE MOTION.]
Having made ourselves acquainted with the motion of the glacier, we are
prepared to examine those rents, fissures, chasms, or, as they are most
usually called, _Crevasses_, by which all glaciers are more or less
intersected. They result from the motion of the glacier, and the laws of
their formation are deduced immediately from those of the motion. The
crevasses are sometimes very deep and numerous, and apparently without
law or order in their distribution. They cut the ice into long ridges,
and break these ridges transversely into prisms; these prisms gradually
waste away, assuming, according to the accidents of their melting, the
most fantastic forms. I have seen them like the mutilated statuary of an
ancient temple, like the crescent moon, like huge birds with
outstretched wings, like the claws of lobsters, and like antlered deer.
Such fantastic sculpture is often to be found on the ice cascades, where
the riven glacier has piled vast blocks on vaster pedestals, and
presented them to the wasting action of sun and air. In Fig. 24 I have
given a sketch of a mass of ice of this character, which stood in 1859
on the dislocated slope of the Glacier des Bois.
[Sidenote: FANTASTIC ICE-MASSES.]
[Illustration: Fig. 24. Fantastic Mass of ice.]
It is usual for visitors to the Montanvert to descend to the glacier,
and to be led by their guides to the edges of the crevasses, where,
being firmly held, they look down into them; but those who have only
made their acquaintance in this way know but little of their magnitude
and beauty in the more disturbed portions of glaciers. As might be
expected, they have been the graves of many a mountaineer; and the
skeletons found upon the glacier prove that even the chamois itself,
with its elastic muscles and admirable sureness of foot, is not always
safe among the crevasses. They are grandest in the higher ice-regions,
where the snow hangs like a coping over their edges, and the water
trickling from these into the gloom forms splendid icicles. The Görner
Glacier, as we ascend it towards the old Weissthor, presents many fine
examples of such crevasses; the ice being often torn in a most curious
and irregular manner. You enter a porch, pillared by icicles, and look
into a cavern in the very body of the glacier, encumbered with vast
frozen bosses which are fringed all round by dependent icicles. At the
peril of your life from slipping, or from the yielding of the
stalactites, you may enter these caverns, and find yourself steeped in
the blue illumination of the place. Their beauty is beyond description;
but you cannot deliver yourself up, heart and soul, to its enjoyment.
There is a strangeness about the place which repels you, and not without
anxiety do you look from your ledge into the darkness below, through
which the sound of subglacial water sometimes rises like the tolling of
distant bells. You feel that, however the cold splendours of the place
might suit a purely spiritual essence, they are not congenial to flesh
and blood, and you gladly escape from its magnificence to the sunshine
of the world above.
[Sidenote: BIRTH OF A CREVASSE.]
From their numbers it might be inferred that the formation of crevasses
is a thing of frequent occurrence and easy to observe; but in reality it
is very rarely observed. Simond was a man of considerable experience
upon the ice, but the first crevasse he ever saw formed was during the
setting out of one of our lines, when a narrow rent opened beneath his
feet, and propagated itself through the ice with loud cracking for a
distance of 50 or 60 yards. Crevasses always commence in this way as
mere narrow cracks, which open very slowly afterwards. I will here
describe the only case of crevasse-forming which has come under my
direct observation.
On the 31st of July, 1857, Mr. Hirst and myself, having completed our
day's work, were standing together upon the Glacier du Géant, when a
loud dull sound, like that produced by a heavy blow, seemed to issue
from the body of the ice underneath the spot on which we stood. This was
succeeded by a series of sharp reports, which were heard sometimes above
us, sometimes below us, sometimes apparently close under our feet, the
intervals between the louder reports being filled by a low singing
noise. We turned hither and thither as the direction of the sounds
varied; for the glacier was evidently breaking beneath our feet, though
we could discern no trace of rupture. For an hour the sounds continued
without our being able to discover their source; this at length revealed
itself by a rush of air-bubbles from one of the little pools upon the
surface of the glacier, which was intersected by the newly-formed
crevasse. We then traced it for some distance up and down, but hardly at
any place was it sufficiently wide to permit the blade of my penknife to
enter it. M. Agassiz has given an animated description of the terror of
his guides upon a similar occasion, and there was an element of awe in
our own feelings as we heard the evening stillness of the glacier thus
disturbed.
[Sidenote: MECHANICAL ORIGIN.]
With regard to the mechanical origin of the crevasses the most vague and
untenable notions had been entertained until Mr. Hopkins published his
extremely valuable papers. To him, indeed, we are almost wholly indebted
for our present knowledge of the subject, my own experiments upon this
portion of the glacier-question being for the most part illustrations of
the truth of his reasoning. To understand the fissures in their more
complex aspects it is necessary that we should commence with their
elements. I shall deal with the question in my own way, adhering,
however, to the mechanical principles upon which Mr. Hopkins has based
his exposition.
[Illustration: Fig. 25. Diagram explanatory of the mechanical origin of
Crevasses.]
Let A B, C D, be the bounding sides of a glacier moving in the direction
of the arrow; let _m_, _n_ be two points upon the ice, one, _m_, close
to the retarding side of the valley, and the other, _n_, at some
distance from it. After a certain time, the point _m_ will have moved
downwards to _m'_, but in consequence of the swifter movement of the
parts at a distance from the sides, _n_ will have moved in the same
time to _n'_. Thus the line _m n_, instead of being at right angles to
the glacier, takes up the oblique position _m' n'_; but to reach from
_m'_ to _n'_ the line _m n_ would have to stretch itself considerably;
every other line that we can draw upon the ice parallel to _m' n'_ is in
a similar state of tension; or, in other words, the sides of the glacier
are acted upon by an oblique pull towards the centre. Now, Mr. Hopkins
has shown that the direction in which this oblique pull is strongest
encloses an angle of 45° with the side of the glacier.
[Sidenote: LINE OF GREATEST STRAIN.]
[Illustration: Fig. 26. Diagram showing the line of Greatest Strain.]
What is the consequence of this? Let A B, C D, Fig. 26, represent, as
before, the sides of the glacier, moving in the direction of the arrow;
let the shading lines enclose an angle of 45° with the sides. _Along_
these lines the marginal ice suffers the greatest strain, and,
consequently _across_ these lines and at right angles to them, the ice
tends to break and to form _marginal crevasses_. The lines, _o p_, _o
p_, mark the direction of these crevasses; they are at right angles to
the line of greatest strain, and hence also enclose an angle of 45° with
the side of the valley, _being obliquely pointed upwards_.
[Sidenote: MARGINAL AND TRANSVERSE CREVASSES.]
This latter result is noteworthy; it follows from the mechanical data
that the swifter motion of the centre tends to produce marginal
crevasses which are inclined from the side of the glacier towards its
source, and not towards its lower extremity. But when we look down upon
a glacier thus crevassed, the first impression is that the sides have
been dragged down, and have left the central portions behind them;
indeed, it was this very appearance that led M. de Charpentier and M.
Agassiz into the error of supposing that the sides of a glacier moved
more quickly than its middle portions; and it was also the delusive
aspect of the crevasses which led Professor Forbes to infer the slower
motion of the eastern side of the Mer de Glace.
The retardation of the ice is most evident near the sides; in most
cases, the ice for a considerable distance right and left of the central
line moves with a sensibly uniform velocity; there is no dragging of the
particles asunder by a difference of motion, and, consequently, a
compact centre is perfectly compatible with fissured sides. Nothing is
more common than to see a glacier with its sides deeply cut, and its
central portions compact; this, indeed, is always the case where the
glacier moves down a bed of uniform inclination.
But supposing that the bed is not uniform--that the valley through which
the glacier moves changes its inclination abruptly, so as to compel the
ice to pass over a brow; the glacier is then circumstanced like a stick
which we try to break by holding its two ends and pressing it against
the knee. The brow, where the bed changes its inclination, represents
the knee in the case of the stick, while the weight of the glacier
itself is the force that tends to break it. It breaks; and fissures are
formed across the glacier, which are hence called _transverse
crevasses_.
[Sidenote: GRINDELWALD GLACIER.]
No glacier with which I am acquainted illustrates the mechanical laws
just developed more clearly and fully than the Lower glacier of
Grindelwald. Proceeding along the ordinary track beside the glacier, at
about an hour's distance from the village the traveller reaches a point
whence a view of the glacier is obtained from the heights above it. The
marginal fissures are very cleanly cut, and point nearly in the
direction already indicated; the glacier also changes its inclination
several times along the distance within the observer's view. On crossing
each brow the glacier is broken across, and a series of transverse
crevasses is formed, which follow each other down the slope. At the
bottom of the slope tension gives place to pressure, the walls of the
crevasses are squeezed together, and the chasms closed up. They remain
closed along the comparatively level space which stretches between the
base of one slope and the brow of the next; but here the glacier is
again transversely broken, and continues so until the base of the second
slope is reached, where longitudinal pressure instead of longitudinal
strain begins to act, and the fissures are closed as before. In Fig. 27A
I have given a sketchy section of a portion of the glacier, illustrating
the formation of the crevasses at the top of a slope, and their
subsequent obliteration at its base.
[Sidenote: COMPRESSION AND TENSION.]
[Illustration: Fig. 27A, B. Section and Plan of a portion of the Lower
Grindelwald Glacier.]
Another effect is here beautifully shown, namely, the union of the
transverse and marginal crevasses to form continuous fissures which
stretch quite across the glacier. Fig. 27B will illustrate my meaning,
though very imperfectly; it represents a plan of a portion of the Lower
Grindelwald glacier, with both marginal and transverse fissures drawn
upon it. I have placed it under the section so that each part of it may
show in plan the portion of the glacier which is shown in section
immediately above it. It shows how the marginal crevasses remain after
the compression of the centre has obliterated the transverse ones; and
how the latter join on to the former, so as to form continuous fissures,
which sweep across the glacier in vast curves, with their convexities
turned upwards. The illusion before referred to is here strengthened;
the crevasses turn, so to say, _against_ the direction of motion,
instead of forming loops, with their convexities pointing downwards, and
thus would impress a person unacquainted with the mechanical data with
the idea that the glacier margins moved more quickly than the centre.
The figures are intended to convey the idea merely; on the actual slopes
of the glacier between twenty and thirty chasms may be counted: also the
word "compression" ought to have been limited to the level portions of
the sketch.
[Sidenote: LONGITUDINAL CREVASSES.]
Besides the two classes of fissures mentioned we often find others,
which are neither marginal nor transverse. The terminal portions of many
glaciers, for example, are in a state of compression; the snout of the
glacier abuts against the ground, and having to bear the thrust of the
mass behind it, if it have room to expand laterally, the ice will
yield, and _longitudinal crevasses_ will be formed. They are of very
common occurrence, but the finest example of the kind is perhaps
exhibited by the glacier of the Rhone. After escaping from the steep
gorge which holds the cascade, this glacier encounters the bottom of a
comparatively wide and level valley; the resistance to its forward
motion is augmented, while its ability to expand laterally is increased;
it has to bear a longitudinal thrust, and it splits at right angles to
the pressure [strain?]. A series of fissures is thus formed, the central
ones of which are truly longitudinal; but on each side of the central
line the crevasses diverge, and exhibit a fan-like arrangement. This
disposition of the fissures is beautifully seen from the summit of the
Mayenwand on the Grimsel Pass.
[Illustration: Fig. 28. Diagram illustrating the crevassing of Convex
Sides of glacier.]
Here then we have the elements, so to speak, of glacier-crevassing, and
through their separate or combined action the most fantastic cutting up
of a glacier may be effected. And see how beautifully these simple
principles enable us to account for the remarkable crevassing of the
eastern side of the Mer de Glace. Let A B, C D, be the opposite sides of
a portion of the glacier, near the Montanvert; C D being east, and A B
west, the glacier moving in the direction of the arrow; let the points
_m n_ represent the extremities of our line of stakes, and let us
suppose an elastic string stretched across the glacier from one to the
other. We have proved that the point of maximum motion here lies much
nearer to the side C D than to A B. Let _o_ be this point, and, seizing
the string at _o_, let it be drawn in the direction of motion until it
assumes the position, _m_, _o'_, _n_. It is quite evident that _o' n_ is
in a state greater tension than _o' m_, and the ice at the eastern side
of the Mer de Glace is in a precisely similar mechanical condition. It
suffers a greater strain than the ice at the opposite side of the
valley, and hence is more fissured and broken. Thus we see that the
crevassing of the eastern side of the glacier is a simple consequence of
the quicker motion of that side, and does not, as hitherto supposed,
demonstrate its slower motion. The reason why the eastern side of the
glacier, as a whole, is much more fissured than the western side is,
that there are two long segments which turn their convex curvature
eastward, and only one segment of the glacier which turns its convexity
westward.
[Sidenote: CREVASSING OF CONVEX SIDE.]
The lower portion of the Rhone glacier sweeps round the side of the
valley next the Furca, and turns throughout a convex curve to this side:
the crevasses here are wide and frequent, while they are almost totally
absent at the opposite side of the glacier. The lower Grindelwald
glacier turns at one place a convex curve towards the Eiger, and is much
more fissured at that side than at the opposite one; indeed, the
fantastic ice-splinters, columns, and minarets, which are so finely
exhibited upon this glacier, are mainly due to the deep crevassing of
the convex side. Numerous other illustrations of the law might, I doubt
not, be discovered, and it would be a pleasant and useful occupation to
one who takes an interest in the subject, to determine, by strict
measurements upon other glaciers, the locus of the point of maximum
motion, and to observe the associated mechanical effects.
[Sidenote: BERGSCHRUNDS.]
The appearance of crevasses is often determined by circumstances more
local and limited than those above indicated; a boss of rock, a
protuberance on the side of the flanking mountain, anything, in short,
which checks the motion of one part of the ice and permits an adjacent
portion to be pushed away from it, produces crevasses. Some valleys are
terminated by a kind of mountain-circus with steep sides, against which
the snow rises to a considerable height. As the mass is urged downwards,
the lower portion of the snow-slope is often torn away from its higher
portion, and a chasm is formed, which usually extends round the head of
the valley. To such a crevasse the specific name _Bergschrund_ is
applied in the Bernese Alps; I have referred to one of them in the
account of the "Passage of the Strahleck."
(18.)
The phenomena described and accounted for in the last chapter have a
direct bearing upon the question of viscosity. In virtue of the quicker
central flow the lateral ice is subject to an oblique strain; but,
instead of stretching, it breaks, and marginal crevasses are formed. We
also see that a slight curvature in the valley, by throwing an
additional strain upon one half of the glacier, produces an augmented
crevassing of that side.
But it is known that a substance confessedly viscous may be broken by a
sudden shock or strain. Professor Forbes justly observes that
sealing-wax at moderate temperatures will mould itself (with time) to
the most delicate inequalities of the surface on which it rests, but may
at the same time be shivered to atoms by the blow of a hammer. Hence, in
order to estimate the weight of the objection that a glacier breaks when
subjected to strain, we must know the conditions under which the force
is applied.
The Mer de Glace has been shown (p. 287) to move through the neck of the
valley at Trélaporte at the rate of twenty inches a day. Let the sides
of this page represent the boundaries of the glacier at Trélaporte, and
any one of its lines of print a transverse slice of ice. Supposing the
line to move down the page as the slice of ice moves down the valley,
then the bending of the ice in twenty-four hours, shown on such a scale,
would only be sufficient to push forward the centre in advance of the
sides by a very small fraction of the width of the line of print. To
such an extremely gradual strain the ice is unable to accommodate itself
without fracture.
[Sidenote: NUMERICAL TEST OF VISCOSITY.]
Or, referring to actual numbers:--the stake No. 15 on our 5th line, page
284, stood on the lateral moraine of the Mer de Glace; and between it
and No. 14 a distance of 190 feet intervened. Let A B, Fig. 29, be the
side of the glacier, moving in the direction of the arrow, and let _a b
c d_ be a square upon the glacier with a side of 190 feet. The whole
square moves with the ice, but the side _b d_ moves quickest; the point
_a_ moving 10 inches, while _b_ moves 14.75 inches in 24 hours; the
differential motion therefore amounts to an inch in five hours. Let _a
b' d' c_ be the shape of the figure after five hours' motion; then the
line _a b_ would be extended to _a b'_ and _c d_ to _c d'_.
[Illustration: Fig. 29. Diagram illustrating test of viscosity.]
The extension of _these_ lines does not however express the _maximum_
strain to which the ice is subjected. Mr. Hopkins has shown that this
takes place along the line _a d_; in five hours then this line, if
capable of stretching, would be stretched to _a d'_. From the data given
every boy who has mastered the 47th Proposition of the First Book of
Euclid can find the length both of _a d_ and _a d'_; the former is
3224.4 inches, and the latter is 3225.1, the difference between them
being seven-tenths of an inch.
This is the amount of yielding required from the ice in five hours, but
it cannot grant this; the glacier breaks, and numerous marginal
crevasses are formed. It must not be forgotten that the evidence here
adduced merely shows what ice cannot do; what it _can_ do in the way of
viscous yielding we do not know: there exists as yet no single
experiment on great masses or small to show that ice possesses in any
sensible degree that power of being drawn out which seems to be the very
essence of viscosity.
I have already stated that the crevasses, on their first formation, are
exceedingly narrow rents, which widen very slowly. The new crevasse
observed by our guide required several days to attain a width of three
inches; while that observed by Mr. Hirst and myself did not widen a
single inch in three days. This, I believe, is the general character of
the crevasses; they form suddenly and open slowly. Both facts are at
variance with the idea that ice is viscous; for were this substance
capable of stretching at the slow rate at which the fissures widen,
there would be no necessity for their formation.
[Sidenote: STRETCHING OF ICE NOT PROVED.]
It cannot be too clearly and emphatically stated that the _proved_ fact
of a glacier conforming to the law of semi-fluid motion is a thing
totally different from the _alleged_ fact of its being viscous. Nobody
since its first enunciation disputed the former. I had no doubt of it
when I repaired to the glaciers in 1856; and none of the eminent men who
have discussed this question with Professor Forbes have thrown any doubt
upon his measurements. It is the assertion that small pieces of ice are
proved to be viscous[A] by the experiments made upon glaciers, and the
consequent impression left upon the public mind--that ice possesses the
"gluey tenacity" which the term viscous suggests--to which these
observations are meant to apply.
FOOTNOTES:
[A] "The viscosity, though it cannot be traced in the parts _if very
minute_ nevertheless _exists_ there, as unequivocally proved by
experiments on the large scale."--Forbes in 'Phil. Mag.,' vol. x., p.
301.
HEAT AND WORK.
(19.)
[Sidenote: CONNEXION OF NATURAL FORCES.]
Great scientific principles, though usually announced by individuals,
are often merely the distinct expression of thoughts and convictions
which had long been entertained by all advanced investigators. Thus the
more profound philosophic thinkers had long suspected a certain
equivalence and connexion between the various forces of nature;
experiment had shown the direct connexion and mutual convertibility of
many of them, and the spiritual insight, which, in the case of the true
experimenter, always surrounds and often precedes the work of his hands,
revealed more or less plainly that natural forces either had a common
root, or that they formed a circle, whose links were so connected that
by starting from any one of them we could go through the circuit, and
arrive at the point from which we set out. For the last eighteen years
this subject has occupied the attention of some of the ablest natural
philosophers, both in this country and on the Continent. The connexion,
however, which has most occupied their minds is that between _heat_ and
_work_; the absolute numerical equivalence of the two having, I believe,
been first announced by a German physician named Mayer, and
experimentally proved in this country by Mr. Joule.
[Sidenote: MECHANICAL EQUIVALENT OF HEAT.]
A lead bullet may be made hot enough to burn the hand, by striking it
with a hammer, or by rubbing it against a board; a clever blacksmith can
make a nail red-hot by hammering it; Count Rumford boiled water by the
heat developed in the boring of cannon, and inferred from the experiment
that heat was not what it was generally supposed to be, an imponderable
fluid, but a kind of motion generated by the friction. Now Mr. Joule's
experiments enable us to state the exact amount of heat which a definite
expenditure of mechanical force can originate. I say _originate_, not
drag from any hiding-place in which it had concealed itself, but
actually bring into existence, so that the total amount of heat in the
universe is thereby augmented. If a mass of iron fall from a tower 770
feet in height, we can state the precise amount of heat developed by its
collision with the earth. Supposing all the heat thus generated to be
concentrated in the iron itself, its temperature would thereby be raised
nearly 10° Fahr. Gravity in this case has expended a certain amount of
force in pulling the iron to the earth, and this force is the
_mechanical equivalent_ of the heat generated. Furthermore, if we had a
machine so perfect as to enable us to apply all the heat thus produced
to the raising of a weight, we should be able, by it, to lift the mass
of iron to the precise point from which it fell.
But the heat cannot lift the weight and still continue heat; this is the
peculiarity of the modern view of the matter. The heat is consumed, used
up, it is no longer heat; but instead of it we have a certain amount of
gravitating force stored up, which is ready to act again, and to
regenerate the heat when the weight is let loose. In fact, when the
falling weight is stopped by the earth, the motion of its mass is
converted into a motion of its molecules; when the weight is lifted by
heat, molecular motion is converted into ordinary mechanical motion, but
for every portion of either of them brought into existence an equivalent
portion of the other must be consumed.
What is true for masses is also true for atoms. As the earth and the
piece of iron mutually attract each other, and produce heat by their
collision, so the carbon of a burning candle and the oxygen of the
surrounding air mutually attract each other; they rush together, and on
collision the arrested motion becomes heat. In the former case we have
the conversion of gravity into heat, in the latter the conversion of
chemical affinity into heat; but in each case the process consists in
the generation of motion by attraction, and the subsequent change of
that motion into motion of another kind. Mechanically considered, the
attraction of the atoms and its results is precisely the same as the
attraction of the earth and weight and _its_ results.
[Sidenote: HEAT PRODUCED IF THE EARTH STRUCK THE SUN.]
But what is true for an atom is also true for a planet or a sun.
Supposing our earth to be brought to rest in her orbit by a sudden
shock, we are able to state the exact amount of heat which would be
thereby generated. The consequence of the earth's being thus brought to
rest would be that it would fall into the sun, and the amount of heat
which would be generated by this second collision is also calculable.
Helmholtz has calculated that in the former case the heat generated
would be equal to that produced by the combustion of fourteen earths of
solid coal, and in the latter case the amount would be 400 times
greater.
[Sidenote: SHIFTING OF ATOMS.]
Whenever a weight is lifted by a steam-engine in opposition to the force
of gravity an amount of heat is consumed equivalent to the work done;
and whenever the molecules of a body are shifted in opposition to their
mutual attractions work is also performed, and an equivalent amount of
heat is consumed. Indeed the amount of work done in the shifting of the
molecules of a body by heat, when expressed in ordinary mechanical work,
is perfectly enormous. The lifting of a heavy weight to the height of
1000 feet may be as nothing compared with the shifting of the atoms of a
body by an amount so small that our finest means of measurement hardly
enable us to determine it. Different bodies give heat different degrees
of trouble, if I may use the term, in shifting their atoms and putting
them in new places. Iron gives more trouble than lead; and water gives
far more trouble than either. The heat expended in this molecular work
is lost as heat; it does not show itself as temperature. Suppose the
heat produced by the combustion of an ounce of candle to be concentrated
in a pound of iron, a certain portion of that heat would go to perform
the molecular work to which I have referred, and the remainder would be
expended in raising the temperature of the body; and if the same amount
of heat were communicated to a pound of iron and to a pound of lead, the
balance in favour of temperature would be greater in the latter case
than in the former, because the heat would have less molecular work to
do; the lead would become more heated than the iron. To raise a pound of
iron a certain number of degrees in temperature would, in fact, require
more than three times the absolute quantity of heat which would be
required to raise a pound of lead the same number of degrees.
Conversely, if we place the pound of iron and the pound of lead, heated
to the same temperature, into ice, we shall find that the quantity of
ice melted by the iron will be more than three times that melted by the
lead. In fact, the greater amount of molecular work invested in the iron
now comes into play, the atoms again obey their own powerful forces, and
an amount of heat corresponding to the energy of these forces is
generated.
This molecular work is that which has usually been called _specific
heat_, or _capacity for heat_. According to the _materialistic_ view of
heat, bodies are figured as sponges, and heat as a kind of fluid
absorbed by them, different bodies possessing different powers of
absorption. According to the _dynamic_ view, as already explained, heat
is regarded as a motion, and capacity for heat indicates the quantity of
that motion consumed in internal changes.
The greatest of these changes occurs when a body passes from one state
of aggregation to another, from the solid to the liquid, or from the
liquid to the aëriform state; and the quantity of heat required for such
changes is often enormous. To convert a pound of ice at 32° Fahr. into
water _at the same temperature_ would require an amount of heat
competent, if applied as mechanical force, to lift the same pound of ice
to a height of 110,000 feet; it would raise a ton of ice nearly 50 feet,
or it would lift between 49 and 50 tons to a height of one foot above
the earth's surface. To convert a pound of water at 212° into a pound of
steam at the same temperature would require an amount of heat which
would perform nearly seven times the amount of mechanical work just
mentioned.
[Sidenote: HEAT CONSUMED IN MOLECULAR WORK.]
This heat is entirely expended in _interior work_,[A] and does nothing
towards augmenting the temperature; the water is at the temperature of
the ice which produced it, both are 32°; and the steam is at the
temperature of the water which produced it, both are 212°. The whole of
the heat is consumed in producing the change of aggregation; I say
"_consumed_," not hidden or "latent" in either the water or the steam,
but absolutely non-existent as heat. The molecular forces, however,
which the heat has sacrificed itself to overcome are able to reproduce
it; the water in freezing and the steam in condensing give out the exact
amount of heat which they consumed when the change of aggregation was in
the opposite direction.
At a temperature of several degrees below its freezing point ice is much
harder than at 32°. I have more than once cooled a sphere of the
substance in a bath of solid carbonic acid and ether to a temperature of
100° below the freezing point. During the time of cooling the ice
crackled audibly from its contraction, and afterwards it quite resisted
the edge of a knife; while at 32° it may be cut or crushed with extreme
facility. The cold sphere was subjected to pressure; it broke with the
detonation of a vitreous body, and was taken from the press a white
opaque powder; which, on being subsequently raised to 32° and again
compressed, was converted into a pellucid slab of ice.
[Sidenote: ICE NEAR THE MELTING POINT.]
But before the temperature of 32° is quite attained, ice gives evidence
of a loosening of its crystalline texture. Indeed the unsoundness of ice
at and near its melting point has been long known. Sir John Leslie, for
example, states that ice at 32° is _friable_; and every skater knows how
rotten ice becomes before it thaws. M. Person has further shown that the
latent heat of ice, that is to say, the quantity of heat necessary for
its liquefaction, is not quite expressed by the quantity consumed in
reducing ice at 32° to the liquid state. The heat begins to be rendered
latent, or in other words the change of aggregation commences, a little
before the substance reaches 32°,--a conclusion which is illustrated and
confirmed by the deportment of melting ice under pressure.
[Sidenote: ROTTEN ICE AND SOFTENED WAX.]
In reference to the above result Professor Forbes writes as follows:--"I
have now to refer to a fact ... established by a French experimenter, M.
Person, who appears not to have had even remotely in his mind the theory
of glaciers, when he announced the following facts, viz.--'That ice does
not pass abruptly from the solid to the fluid state; that it begins to
_soften_ at a temperature of 2° Centigrade below its thawing point;
that, consequently, between 28° 4' and 32° of Fahr. ice is actually
passing through various degrees of plasticity within narrower limits,
but in the same manner that wax, for example, softens before it melts.'"
The "_softening_" here referred to is the "friability," of Sir J.
Leslie, and what I have called a "loosening of the texture." Let us
suppose the Serpentine covered by a sheet of pitch so smooth and hard as
to enable a skater to glide over it; and which is afterwards gradually
warmed until it begins to bend under his weight, and finally lets him
through. A comparison of this deportment with that of a sheet of ice
under the same circumstances enables us to decide whether ice "passes
through various degrees of plasticity in the same manner as wax softens
before it melts." M. Person concerned himself solely with the heat
absorbed, and no doubt in both wax and ice that heat is expended in
"interior work." In the one case, however, the body is so constituted
that the absorbed heat is expended in rendering the substance viscous;
and the question simply is, whether the heat absorbed by the ice gives
its molecules a freedom of play which would entitle it also to be called
viscous; whether, in short, "rotten ice" and softened wax present the
same physical qualities?
FOOTNOTES:
[A] I borrow this term from Professor Clausius's excellent papers on the
Dynamical Theory of Heat.
(20.)
There is one other point in connexion with the viscous theory which
claims our attention. The announcement of that theory startled
scientific men, and for two or three years after its first publication
it formed the subject of keen discussion. This finally subsided, and
afterwards Professor Forbes drew up an elaborate paper, which was
presented in three parts to the Royal Society in 1845 and 1846, and
subsequently published in the 'Philosophical Transactions.'
In the concluding portion of Part III. Professor Forbes states and
answers the question, "How far a glacier is to be regarded as a plastic
mass?" in these words:--"Were a glacier composed of a solid crystalline
cake of ice, fitted or moulded to the mountain bed which it occupies,
like a lake tranquilly frozen, it would seem impossible to admit such a
flexibility or yielding of parts as should permit any comparison to a
fluid or semifluid body, transmitting pressure horizontally, and whose
parts might change their mutual positions so that one part should be
pushed out whilst another remained behind. But we know, in point of
fact, that a glacier is a body very differently constituted. It is
clearly proved by the experiments of Agassiz and others that the glacier
is not a mass of ice, but of ice and water, the latter percolating
freely through the crevices of the former to all depths of the glacier;
and it is a matter of ocular demonstration that these crevices, though
very minute, communicate freely with one another to great distances; the
water with which they are filled communicates force also to great
distances, and exercises a tremendous hydrostatic pressure to move
onwards in the direction in which gravity urges it, the vast porous mass
of seemingly rigid ice in which it is as it were bound up."
[Sidenote: CAPILLARY HYPOTHESIS.]
"Now the water in the crevices," continues Professor Forbes, "does not
constitute the glacier, but only the principal vehicle of the force
which acts on it, and the slow irresistible energy with which the icy
mass moves onwards from hour to hour with a continuous march, bespeaks
of itself the presence of a fluid pressure. But if the ice were not in
some degree ductile or plastic, this pressure could never produce any
the least forward motion of the mass. The pressure in the capillaries of
the glacier can only tend to separate one particle from another, and
thus produce tensions and compressions _within the body of the glacier
itself_, which yields, owing to its slightly ductile nature, in the
direction of least resistance, retaining its continuity, or recovering
it by reattachment after its parts have suffered a bruise, according to
the violence of the action to which it has been exposed."
I will not pretend to say that I fully understand this passage, but,
taking it and the former one together, I think it is clear that the
water which is supposed to gorge the capillaries of the glacier is
assumed to be essential to its motion. Indeed, an extreme degree of
sensitiveness has been ascribed to the glacier as regards the changes of
temperature by which the capillaries are affected. In three succeeding
days, for example, Professor Forbes found the diurnal summer motion of a
point upon the Mer de Glace to increase from 15.2 to 17.5 inches a day;
a result which he says he is "persuaded" to be due to the increasing
heat of the weather at the time. If, then, the glacier capillaries can
be gorged so quickly as this experiment would indicate, it is fair to
assume that they are emptied with corresponding speed when the supply is
cut away.
[Sidenote: TEMPERATURE AT CHAMOUNI; WINTER 1859.]
The extraordinary coldness of the weather previous to the Christmas of
1859 is in the recollection of everybody: this lowness of temperature
also extended to the Mer de Glace and its environs. I had last summer
left with Auguste Balmat and the Abbé Vueillet thermometers with which
observations were made daily during the cold weather referred to. I take
the following from Balmat's register.
Minimum
Date. temperature
Centigrade.
December 16 -15°
" 17 -20
" 18 -16-1/2
" 19 -9
" 20 -13
" 21 -20-1/2
" 22 -4-1/4
December 23 -4-1/2°
" 24 -6-1/2
" 25 -2
" 26 +2
" 27 -3
" 28 -10-1/2
" 29 -6
The temperature at the Montanvert during the above period may be assumed
as generally some degrees lower, so that for a considerable period,
previous to my winter observations, the portion of the Mer de Glace near
the Montanvert had been exposed to a very low temperature. I reached
the place after the weather had become warm, but during my stay there
the maximum temperature did not exceed -4-1/2° C. Considering therefore
the long drain to which the glacier had been subjected previous to the
29th of December, it is not unreasonable to infer that the capillary
supply assumed by Professor Forbes must by that time have been
exhausted. Notwithstanding this, the motion of the glacier at the
Montanvert amounted at the end of December to half its maximum summer
motion.
[Sidenote: BALMAT'S MEASUREMENTS.]
The observations of Balmat which have been published by Professor
Forbes[A] also militate, as far as they go, against the idea of
proportionality between the capillary supply and the motion. If the
temperatures recorded apply to the Mer de Glace during the periods of
observation, it would follow that from the 19th of December 1846 to the
12th of April 1847 the temperature of the air was constantly under zero
Centigrade, and hence, during this time, the gorging of the capillaries,
which is due to superficial melting, must have ceased. Still, throughout
this entire period of depletion the motion of the glacier steadily
increased from twenty-four inches to thirty-four and a half inches a
day. What has been here said of the Montanvert, and of the points lower
down where Balmat's measurements were made, of course applies with
greater force to the higher portions of the glacier, which are withdrawn
from the operation of superficial melting for a longer period, and
which, nevertheless, if I understand Professor Forbes aright, have their
motion _least affected_ in winter. He records, for example, an
observation of Mr. Bakewell's, by which the Glacier des Bossons is shown
to be stationary at its end, while its upper portions are moving at the
rate of a foot a day. This surely indicates that, at those places where
the glacier is longest cut off from superficial supply, the motion is
least reduced, which would be a most strange result if the motion
depended, as affirmed, upon the gorging of the capillaries.
[Sidenote: BAKEWELL'S OBSERVATIONS.]
The perusal of the conclusion of Professor Forbes's last volume shows me
that a thought similar to that expressed above occurred to Mr. Bakewell
also. Speaking of a shallow glacier which moved when the alleged
temperature was so enormously below the freezing point that Professor
Forbes regards the observation as open to question (in which I agree
with him), Mr. Bakewell asks, "Is it possible that infiltrated water can
have any action whatever under such circumstances?" The reply of
Professor Forbes contains these words:--"I have nowhere affirmed the
presence of liquid water to be a _sine quâ non_ to the plastic motion of
glaciers." This statement, I confess, took me by surprise, which was not
diminished by further reading. Speaking of the influence of temperature
on the motion of the Mer de Glace, Professor Forbes says, the glacier
"took no real start until the frost had given way, and the tumultuous
course of the Arveiron showed that its veins were again filled with the
circulating medium to which the glacier, like the organic frame, owes
its moving energy."[B] And again:--"It is this fragility precisely
which, yielding to the hydrostatic pressure of the unfrozen water
contained in the countless capillaries of the glacier, produces the
crushing action which shoves the ice over its neighbour particles."[C]
[Sidenote: HUXLEY'S OBSERVATIONS.]
After the perusal of the foregoing paragraphs the reader will probably
be less interested in the question as to whether the assumed capillaries
exist at all in the glacier. According to Mr. Huxley's observations,
they do not.[D] During the summer of 1857 he carefully experimented with
coloured liquids on the Mer de Glace and its tributaries, and in no case
was he able to discover these fissures in the sound unweathered ice. I
have myself seen the red liquid resting in an auger-hole, where it had
lain for an hour without diffusing itself in any sensible degree. This
cavity intersected both the white ice and the blue veins of the glacier;
and Mr. Huxley, in my presence, cut away the ice until the walls of the
cavity became extremely thin, still no trace of liquid passed through
them. Experiments were also made upon the higher portions of the Mer de
Glace, and also on the Glacier du Géant, with the same result. Thus the
very existence of these capillaries is rendered so questionable, that no
theory of glacier-motion which invokes their aid could be considered
satisfactory.
FOOTNOTES:
[A] 'Occ. Pap.,' p. 224.
[B] 'Phil. Trans.,' 1846, p. 137, and 'Occ. Pap.,' p. 138.
[C] 'Occ. Pap.,' p. 47.
[D] 'Phil. Mag.,' 1857, vol. xiv., p. 241.
THOMSON'S THEORY.
(21.)
In the 'Transactions' of the Royal Society of Edinburgh for 1849 is
published a very interesting paper by Prof. James Thomson of Queen's
College, Belfast, wherein he deduces, as a consequence of a principle
announced by the French philosopher Carnot, that water, when subjected
to pressure, requires a greater cold to freeze it than when the pressure
is removed. He inferred that the lowering of the freezing point for
every atmosphere of pressure amounted to .0075 of a degree Centigrade.
This deduction was afterwards submitted to the test of experiment by his
distinguished brother Prof. Wm. Thomson, and proved correct. On the fact
thus established is founded Mr. James Thomson's theory of the
"Plasticity of Ice as manifested in Glaciers."
[Sidenote: STATEMENT OF THEORY.]
The theory is this:--Certain portions of the glacier are supposed first
to be subjected to pressure. This pressure liquefies the ice, the water
thus produced being squeezed through the glacier in the direction in
which it can most easily escape. But cold has been evolved by the act of
liquefaction, and, when the water has been relieved from the pressure,
it freezes in a new position. The pressure being thus abolished at the
place where it was first applied, new portions of the ice are subjected
to the force; these in their turn liquefy, the water is dispersed as
before, and re-frozen in some other place. To the succession of
processes here assumed Mr. Thomson ascribes the changes of form observed
in glaciers.
This theory was first communicated to the Royal Society through the
author's brother, Prof. William Thomson, and is printed in the
'Proceedings' of the Society for May, 1857. It was afterwards
communicated to the British Association in Dublin, in whose 'Reports'
it is further published; and again it was communicated to the Belfast
Literary and Philosophical Society, in whose 'Proceedings' it also finds
a place.
On the 24th of November, 1859, Mr. James Thomson communicated to the
Royal Society, through his brother, a second paper, in which he again
draws attention to his theory. He offers it in substitution for my views
as the best argument that he can adduce against them; he also
controverts the explanations of regelation propounded by Prof. James D.
Forbes and Prof. Faraday, believing that his own theory explains all the
facts so well as to leave room for no other.
[Sidenote: DIFFICULTIES OF THEORY.]
But the passage in this paper which demands my chief attention is the
following:--"Prof. Tyndall (writes Mr. Thomson), in papers and lectures
subsequent to the publication of this theory, appears to adopt it to
some extent, and to endeavour to make its principles co-operate with the
views he had previously founded on Mr. Faraday's fact of regelation." I
may say that Mr. Thomson's main thought was familiar to me long before
his first communication on the plasticity of ice appeared; but it had
little influence upon my convictions. Were the above passage correct, I
should deserve censure for neglecting to express my obligations far more
explicitly than I have hitherto done; but I confess that even now I do
not understand the essential point of Mr. Thomson's theory,--that is to
say, its application to the phenomena of glacier motion. Indeed, it was
the obscurity in my mind in connexion with this point, and the hope that
time might enable me to seize more clearly upon his meaning, which
prevented me from giving that prominence to the theory of Mr. Thomson
which, for aught I know, it may well deserve. I will here briefly state
one or two of my difficulties, and shall feel very grateful to have them
removed.
[Sidenote: IMPROBABLE DEDUCTION.]
Let us fix our attention on a vertical slice of ice transverse to the
glacier, and to which the pressure is applied perpendicular to its
surfaces. The ice liquefies, and, supposing the means of escape offered
to the compressed water to be equal all round, it is plain that there
will be as great a tendency to squeeze the water upwards as downwards;
for the mere tendency to flow down by its own gravity becomes, in
comparison to the forces here acting on the water, a vanishing quantity.
But the fact is, that the ice above the slice is more permeable than
that below it; for, as we descend a glacier, the ice becomes more
compact. Hence the greater part of the dispersed water will be refrozen
on that side of the slice which is turned towards the origin of the
glacier; and the consequence is, that, according to Mr. Thomson's
principle, the glacier ought to move up hill instead of down.
I would invite Mr. Thomson to imagine himself and me together upon the
ice, desirous of examining this question in a philosophic spirit; and
that we have taken our places beside a stake driven into the ice, and
descending with the glacier. We watch the ice surrounding the stake, and
find that every speck of dirt upon it retains its position; there is no
liquefaction of the ice that bears the dirt, and consequently it rests
on the glacier undisturbed. After twelve hours we find the stake fifteen
inches distant from its first position: I would ask Mr. Thomson how did
it get there? Or let us fix our attention on those six stakes which M.
Agassiz drove into the glacier of the Aar in 1841, and found erect in
1842 at some hundreds of feet from their first position:--how did they
get there? How, in fine, does the end of a glacier become its end? Has
it been liquefied and re-frozen? If not, it must have been _pushed_ down
by the very forces which Mr. Thomson invokes to produce his
liquefaction. Both the liquefaction, as far as it exists, and the
motion, are products of the same cause. In short, this theory, as it
presents itself to my mind, is so powerless to account for the simplest
fact of glacier-motion, that I feel disposed to continue to doubt my own
competence to understand it rather than ascribe to Mr. Thomson an
hypothesis apparently so irrelevant to the facts which it professes to
explain.
Another difficulty is the following:--Mr. Thomson will have seen that I
have recorded certain winter measurements made on the Mer de Glace, and
that these measurements show not only that the ice moves at that period
of the year, but that it exhibits those characteristics of motion from
which its plasticity has been inferred; the velocity of the central
portions of the glacier being in round numbers double the velocity of
those near the sides. Had there been any necessity for it, this ratio
might have been augmented by placing the side-stakes closer to the walls
of the glacier. Considering the extreme coldness of the weather which
preceded these measurements, it is a moderate estimate to set down the
temperature of the ice in which my stakes were fixed at 5° Cent. below
zero.
[Sidenote: REQUISITE PRESSURE CALCULATED.]
Let us now endeavour to estimate the pressure existing at the portion of
the glacier where these measurements were made. The height of the
Montanvert above the sea-level is, according to Prof. Forbes, 6300 feet;
that of the Col du Géant, which is the summit of the principal tributary
of the Mer de Glace, is 11,146 feet: deducting the former from the
latter, we find the height of the Col du Géant above the Montanvert to
be 4846 feet.
Now, according to Mr. Thomson's theory and his brother's experiments,
the melting point of ice is lowered .0075° Centigrade for every
atmosphere of pressure; and one atmosphere being equivalent to the
pressure of about thirty-three feet of water, we shall not be over the
truth if we take the height of an equivalent column of glacier-ice, of a
compactness the mean of those which it exhibits upon the Col du Géant
and at the Montanvert respectively, at forty feet. The compactness of
glacier ice is, of course, affected by the air-bubbles contained within
it.
[Sidenote: ACTUAL PRESSURE INSUFFICIENT.]
If, then, the pressure of forty feet of ice lower the melting point
.0075° Centigrade, it follows that the pressure of a column 4846 feet
high will lower it nine-tenths of a degree Centigrade. Supposing, then,
the _unimpeded thrust of the whole glacier, from the Col du Géant
downwards_, to be exerted on the ice at the Montanvert; or, in other
words, supposing the bed of the glacier to be absolutely smooth and
every trace of friction abolished, the utmost the pressure thus obtained
could perform would be to lower the melting point of the Montanvert ice
by the quantity above mentioned. Taking into account the actual state of
things, the friction of the glacier against its sides and bed, the
opposition which the three tributaries encounter in the neck of the
valley at Trélaporte, the resistance encountered in the sinuous valley
through which it passes; and finally, bearing in mind the comparatively
short length of the glacier, which has to bear the thrust, and oppose
the latter by its own friction merely;--I think it will appear evident
that the ice at the Montanvert cannot possibly have its melting point
lowered by pressure more than a small fraction of a degree.
The ice in which my stakes were fixed being -5° Centigrade, according to
Mr. Thomson's calculation and his brother's experiments, it would
require 667 atmospheres of pressure to liquefy it; in other words, it
would require the unimpeded pressure of a column of glacier-ice 26,680
feet high. Did Mont Blanc rise to two and a half times its present
height above the Montanvert, and were the latter place connected with
the summit of the mountain by a continuous glacier with its bed
absolutely smooth, the pressure at the Montanvert would be rather under
that necessary to liquefy the ice on which my winter observations were
made.
[Sidenote: MEASUREMENTS APPLY TO SURFACE.]
If it be urged that, though the temperature near the surface may be
several degrees below the freezing point, the great body of the glacier
does not share this temperature, but is, in all probability, near to
32°, my reply is simple. I did not measure the motion of the ice in the
body of the glacier; nobody ever did; my measurements refer to the ice
at and near the surface, and it is this ice which showed the plastic
deportment which the measurements reveal.
Such, then, are some of the considerations which prevent me from
accepting the theory of Mr. Thomson, and I trust they will acquit me of
all desire, to make his theory co-operate with my views. I am, however,
far from considering his deduction the less important because of its
failing to account for the phenomena of glacier motion.
THE PRESSURE-THEORY OF GLACIER-MOTION.
(22.)
[Sidenote: POSSIBLE MOULDING OF ICE.]
Broadly considered, two classes of facts are presented to the
glacier-observer; the one suggestive of viscosity, and the other of the
reverse. The former are seen where _pressure_ comes into play, the
latter where _tension_ is operative. By pressure ice can be moulded to
any shape, while the same ice snaps sharply asunder if subjected to
tension. Were the result worth the labour, ice might be moulded into
vases or statuettes, bent into spiral bars, and, I doubt not, by the
proper application of pressure, a _rope_ of ice might be formed and
coiled into a _knot_. But not one of these experiments, though they
might be a thousandfold more striking than any ever made upon a glacier,
would in the least demonstrate that ice is really a viscous body.
[Illustration: Fig. 30. Moulds used in experiments with ice.]
I have here stated what I believe to be feasible. Let me now refer to
the experiments which have been actually made in illustration of this
point. Two pieces of seasoned box-wood had corresponding cavities
hollowed in them, so that, when one was placed upon the other, a
lenticular space was enclosed. A and B, Fig. 30, represent the pieces
of box-wood with the cavities in plan: C represents their section when
they are placed upon each other.
[Sidenote: ACTUAL MOULDING OF ICE.]
A _sphere_ of ice rather more than sufficient to fill the lenticular
space was placed between the pieces of wood and subjected to the action
of a small hydraulic press. The ice was crushed, but the crushed
fragments soon reattached themselves, and, in a few seconds, a lens of
compact ice was taken from the mould.
[Illustration: Fig. 31. Moulds used in experiments with ice.]
This lens was placed in a cylindrical cavity hollowed out in another
piece of box-wood, and represented at C, Fig. 31; and a flat piece of
the wood was placed over the lens as a cover, as at D. On subjecting the
whole to pressure, the lens broke, as the sphere had done, but the
crushed mass soon re-established its continuity, and in less than half a
minute a compact cake of ice was taken from the mould.
[Illustration: Fig. 32. Moulds used in experiments with ice.]
In the following experiment the ice was subjected to a still severer
test:--A hemispherical cavity was formed in one block of box-wood, and
upon a second block a hemispherical protuberance was turned, smaller
than the cavity, so that, when the latter was placed in the former, a
space of a quarter of an inch existed between the two. Fig. 32
represents a section of the two pieces of box-wood; the brass pins _a_,
_b_, fixed in the slab G H, and entering suitable apertures in the mould
I K, being intended to keep the two surfaces concentric. A lump of ice
being placed in the cavity, the protuberance was brought down upon it,
and the mould subjected to hydraulic pressure: after a short interval
the ice was taken from the mould as a smooth compact _cup_, its crushed
particles having reunited, and established their continuity.
[Sidenote: ICE MOULDED TO CUPS AND RINGS.]
[Illustration: Fig. 33. Moulds used in experiments with ice.]
To make these results more applicable to the bending of glacier-ice, the
following experiments were made:--A block of box-wood, M, Fig. 33, 4
inches long, 3 wide, and 3 deep, had its upper surface slightly curved,
and a groove an inch wide, and about an inch deep, worked into it. A
corresponding plate was prepared, having its under surface part of a
convex cylinder, of the same curvature as the concave surface of the
former piece. When the one slab was placed upon the other, they
presented the appearance represented in section at N. A straight prism
of ice 4 inches long, an inch wide, and a little more than an inch in
depth, was placed in the groove; the upper slab was placed upon it, and
the whole was subjected to the hydraulic press. The prism broke, but,
the quantity of ice being rather more than sufficient to fill the
groove, the pressure soon brought the fragments together and
re-established the continuity of the ice. After a few seconds it was
taken from the mould a bent bar of ice. This bar was afterwards passed
through three other moulds of gradually augmenting curvature, and was
taken from the last of them a _semi-ring_ of compact ice.
The ice, in changing its form from that of one mould to that of another,
was in every instance broken and crushed by the pressure; but suppose
that instead of three moulds three thousand had been used; or, better
still, suppose the curvature of a single mould to change by extremely
slow degrees; the ice would then so gradually change its form that no
rude rupture would be apparent. Practically the ice would behave as a
_plastic_ substance; and indeed this plasticity has been contended for
by M. Agassiz, in opposition to the idea of viscosity. As already
stated, the ice, bruised, and flattened, and bent in the above
experiments, was incapable of being sensibly stretched; it was plastic
to pressure but not to tension.
A quantity of water was always squeezed out of the crushed ice in the
above experiments, and the bruised fragments were intermixed with this
and with air. Minute quantities of both remained in the moulded ice, and
thus rendered it in some degree turbid. Its character, however, as to
continuity may be inferred from the fact that the ice-cup, moulded as
described, held water without the slightest visible leakage.
[Sidenote: SOFTNESS OF ICE DEFINED.]
[Sidenote: PRESSURE AND TENSION.]
Ice at 32° may, as already stated, be crushed with extreme facility, and
glacier-ice with still more readiness than lake-ice: it may also be
scraped with a knife with even greater facility than some kinds of
chalk. In comparison with ice at 100° below the freezing point, it might
be popularly called _soft_. But its softness is not that of paste, or
wax, or treacle, or lava, or honey, or tar. It is the softness of
calcareous spar in comparison with that of rock-crystal; and although
the latter is incomparably harder than the former, I think it will be
conceded that the term viscous would be equally inapplicable to both. My
object here is clearly to define terms, and not permit physical error to
lurk beneath them. How far this ice, with a softness thus defined, when
subjected to the gradual pressures exerted in a glacier, is bruised and
broken, and how far the motion of its parts may approach to that of a
truly viscous body under pressure, I do not know. The critical point
here is that the ice changes its form, and preserves its continuity,
during its motion, in virtue of _external_ force. It remains continuous
whilst it moves, because its particles are kept in juxtaposition by
pressure, and when this external prop is removed, and the ice, subjected
to tension, has to depend solely upon the mobility of its own particles
to preserve its continuity, the analogy with a viscous body instantly
breaks down.[A]
FOOTNOTES:
[A] "Imagine," writes Professor Forbes, "a long narrow trough or canal,
stopped at both ends and filled to a considerable depth with treacle,
honey, tar, or any such viscid fluid. Imagine one end of the trough to
give way, the bottom still remaining horizontal: if the friction of the
fluid against the bottom be greater than the friction against its own
particles, the upper strata will roll over the lower ones, and protrude
in a convex slope, which will be propagated backwards towards the other
or closed end of the trough. Had the matter been quite fluid the whole
would have run out, and spread itself on a level: as it is, it assumes
precisely the conditions which we suppose to exist in a glacier." This
is perfectly definite, and my equally definite opinion is that no
glacier ever exhibited the mechanical effects implied by this
experiment.
REGELATION.
(23.)
[Sidenote: FARADAY'S FIRST EXPERIMENT.]
I was led to the foregoing results by reflecting on an experiment
performed by Mr. Faraday, at a Friday evening meeting of the Royal
Institution, on the 7th of June, 1850, and described in the 'Athenæum'
and 'Literary Gazette' for the same month. Mr. Faraday then showed that
when two pieces of ice, with moistened surfaces, were placed in contact,
they became cemented together by the freezing of the film of water
between them, while, when the ice was below 32° Fahr., and therefore
_dry_, no effect of the kind could be produced. The freezing was also
found to take place under water; and indeed it occurs even when the
water in which the ice is plunged is as hot as the hand can bear.
A generalisation from this interesting fact led me to conclude that a
bruised mass of ice, if closely confined, must re-cement itself when its
particles are brought into contact by pressure; in fact, the whole of
the experiments above recorded immediately suggested themselves to my
mind as natural deductions from the principle established by Faraday. A
rough preliminary experiment assured me that the deductions would stand
testing; and the construction of the box-wood moulds was the
consequence. We could doubtless mould many solid substances to any
extent by suitable pressure, breaking the attachment of their particles,
and re-establishing a certain continuity by the mere force of cohesion.
With such substances, to which we should never think of applying the
term viscous, we might also imitate the changes of form to which
glaciers are subject: but, superadded to the mere cohesion which here
comes into play, we have, in the case of ice, the actual regelation of
the severed surfaces, and consequently a more perfect solid. In the
Introduction to this book I have referred to the production of slaty
cleavage by pressure; and at a future page I hope to show that the
lamination of the ice of glaciers is due to the same cause; but, as
justly observed by Mr. John Ball, there is no tendency to cleave in the
_sound_ ice of glaciers; in fact, this tendency is obliterated by the
perfect regelation of the severed surfaces.
[Sidenote: RECENT EXPERIMENTS OF FARADAY.]
Mr. Faraday has recently placed pieces of ice, in water, under the
strain of forces tending to pull them apart. When two such pieces touch
at a single point they adhere and move together as a rigid piece; but a
little lateral force carefully applied breaks up this union with a
crackling noise, and a new adhesion occurs which holds the pieces
together in opposition to the force which tends to divide them. Mr.
James Thomson had referred regelation to the cold produced by the
liquefaction of the pressed ice; but in the above experiment all
pressure is not only taken away, but is replaced by tension. Mr. Thomson
also conceives that, when pieces of ice are simply placed together
without intentional pressure, the capillary attraction brings the
pressure of the atmosphere into play; but Mr. Faraday finds that
regelation takes place _in vacuo_. A true viscidity on the part of ice
Mr. Faraday never has observed, and he considers that his recent
experiments support the view originally propounded by himself, namely,
that a particle of water on a surface of ice becomes solid when placed
between two surfaces, because of the increased influence due to their
joint action.
CRYSTALLIZATION AND INTERNAL LIQUEFACTION.
(24.)
[Sidenote: HOW CRYSTALS ARE "NURSED."]
In the Introduction to this book I have briefly referred to the force of
crystallization. To permit this force to exercise its full influence, it
must have free and unimpeded action; a crystal, for instance, to be
properly built, ought to be suspended in the middle of the crystallizing
solution, so that the little architects can work all round it; or if
placed upon the bottom of a vessel, it ought to be frequently turned, so
that all its facets may be successively subjected to the building
process. In this way crystals can be _nursed_ to an enormous size. But
where other forces mingle with that of crystallization, this harmony of
action is destroyed; the figures, for example, that we see upon a glass
window, on a frosty morning, are due to an action compounded of the pure
crystalline force and the cohesion of the liquid to the window-pane. A
more regular effect is obtained when the freezing particles are
suspended in still air, and here they build themselves into those
wonderful figures which Dr. Scoresby has observed in the Polar Regions,
Mr. Glaisher at Greenwich, and I myself on the summit of Monte Rosa and
elsewhere.
Not only however in air, but in water also, figures of great beauty are
sometimes formed. Harrison's excellent machine for the production of
artificial ice is, I suppose, now well known; the freezing being
effected by carrying brine, which had been cooled by the evaporation of
ether, round a series of flat tin vessels containing water. The latter
gradually freezes, and, on watching those vessels while the action was
proceeding very slowly, I have seen little six-rayed stars of thin ice
forming, and rising to the surface of the liquid. I believe the fact
was never before observed, but it would be interesting to follow it up,
and to develop experimentally this most interesting case of
crystallization.
[Sidenote: DISSECTION OF ICE BY SUNBEAM.]
The surface of a freezing lake presents to the eye of the observer
nothing which could lead him to suppose that a similar molecular
architecture is going on there. Still the particles are undoubtedly
related to each other in this way; they are arranged together on this
starry type. And not only is this the case at the surface, but the
largest blocks of ice which reach us from Norway and the Wenham Lake are
wholly built up in this way. We can reveal the internal constitution of
these masses by a reverse process to that which formed them; we can send
an agent into the interior of a mass of ice which shall take down the
atoms which the crystallizing forces had set up. This agent is a solar
beam; with which it first occurred to me to make this simple experiment
in the autumn of 1857. I placed a large converging lens in the sunbeams
passing through a room, and observed the place where the rays were
brought to a focus behind the lens; then shading the lens, I placed a
clear cube of ice so that the point of convergence of the rays might
fall within it. On removing the screen from the lens, a cone of sunlight
went through the cube, and along the course of the cone the ice became
studded with lustrous spots, evidently formed by the beam, as if minute
reflectors had been suddenly established within the mass, from which the
light flashed when it met them. On examining the cube afterwards I found
that each of these spots was surrounded by a liquid flower of six
petals; such flowers were distributed in hundreds through the ice, being
usually clear and detached from each other, but sometimes crowded
together into liquid bouquets, through which, however, the six-starred
element could be plainly traced. At first the edges of the leaves were
unbroken curves, but when the flowers expanded under a long-continued
action, the edges became serrated. When the ice was held at a suitable
angle to the solar beams, these liquid blossoms, with their central
spots shining more intensely than burnished silver, presented an
exhibition of beauty not easily described. I have given a sketch of
their appearance in Fig. 34.
[Sidenote: LIQUID FLOWERS IN ICE.]
[Illustration: Fig. 34. Liquid Flowers in lake ice.]
I have here to direct attention to an extremely curious fact. On sending
the sunbeam through the transparent ice, I often noticed that the
appearance of the lustrous spots was accompanied by an audible clink, as
if the ice were ruptured inwardly. But there is no ground for assuming
such rupture, and on the closest examination no flaw is exhibited by the
ice. What then can be the cause of the noise? I believe the following
considerations will answer the question:--
Water always holds a quantity of air in solution, the diffusion of which
through the liquid, as proved by M. Donny, has an immense effect in
weakening the cohesion of its particles; recent experiments of my own
show that this is also the case in an eminent degree with many volatile
liquids. M. Donny has proved that, if water be thoroughly purged of its
air, a long glass tube filled with this liquid may be inverted, while
the tenacity with which the water clings to the tube, and with which its
particles cling to each other, is so great that it will remain securely
suspended, though no external hindrance be offered to its descent. Owing
to the same cause, water deprived of its air will not boil at 212°
Fahr., and may be raised to a temperature of nearly 300° without
boiling; but when this occurs the particles break their cohesion
suddenly, and ebullition is converted into explosion.
Now, when ice is formed, every trace of the air which the water
contained is squeezed out of it; the particles in crystallizing reject
all extraneous matter, so that in ice we have a substance quite free
from the air, which is never absent in the case of water; it therefore
follows that if we could preserve the water derived from the melting of
ice from contact with the atmosphere, we should have a liquid eminently
calculated to show the effects described by M. Donny. Mr. Faraday has
proved by actual experiment that this is the case.
[Sidenote: WATER DEPRIVED OF AIR SNAPS ASUNDER.]
Let us apply these facts to the explanation of the clink heard in my
experiments. On sending a sunbeam through ice, liquid cavities are
suddenly formed at various points within the mass, and these cavities
are completely cut off from atmospheric contact. But the water formed by
the melting ice is less in volume than the ice which produces it; the
water of a cavity is not able to fill it, hence a vacuous space must be
formed in the cell. I have no doubt that, for a time, the strong
cohesion between the walls of the cell and the drop within it augments
the volume of the latter a little, so as to compel it to fill the cell;
but as the quantity of liquid becomes greater the shrinking force
augments, until finally the particles snap asunder like a broken spring.
At the same moment a lustrous spot appears, which is a vacuum, and
simultaneously with the appearance of this vacuum the clink was always
heard. Multitudes of such little explosions must be heard upon a glacier
when the strong summer sun shines upon it, the aggregate of which must,
I think, contribute to produce the "crepitation" noticed by M. Agassiz,
and to which I have already referred.
[Sidenote: FIGURES IN ICE; VACUOUS SPOTS.]
In Plate VI. of the Atlas which accompanies the 'Système Glaciaire' of
M. Agassiz, I notice drawings of figures like those I have described,
which he has observed in glacier-ice, and which were doubtless produced
by direct solar radiation. I have often myself observed figures of
exquisite beauty formed in the ice on the surface of glacier-pools by
the morning sun. In some cases the spaces between the leaves of the
liquid flowers melt partially away, and leave the central spot
surrounded by a crimped border; sometimes these spaces wholly disappear,
and the entire space bounded by the lines drawn from point to point of
the leaves becomes liquid, thus forming perfect hexagons. The crimped
borders exhibit different degrees of serration, from the full leaves
themselves to a gentle undulating line, which latter sometimes merges
into a perfect circle. In the ice of glaciers, I have seen the internal
liquefaction ramify itself like sprigs of myrtle; in the same ice, and
particularly towards the extremities of the glacier, disks innumerable
are also formed, consisting of flat round liquid spaces, a bright spot
being usually associated with each. These spots have been hitherto
mistaken for air-bubbles; but both they and the lustrous disks at the
centres of the flowers are vacuous. I proved them to be so by plunging
the ice containing them into hot water, and watching what occurred when
the walls of the cells were dissolved, and a liquid connexion
established between them and the atmosphere. In all cases they totally
collapsed, and no trace of air rose to the surface of the warm water.
No matter in what direction a solar beam is sent through lake-ice, the
liquid flowers are all formed parallel to the surface of freezing. The
beam may be sent parallel, perpendicular, or oblique to this surface;
the flowers are always formed in the same planes. Every line
perpendicular to the surface of a frozen lake is in fact an axis of
symmetry, round which the molecules so arrange themselves, that, when
taken down by the delicate fingers of the sunbeam, the six-leaved liquid
flowers are the result.
In the ice of glaciers we have no definite planes of freezing. It is
first snow, which has been disturbed by winds while falling, and whirled
and tossed about by the same agency after it has fallen, being often
melted, saturated with its own water, and refrozen: it is cast in
shattered fragments down cascades, and reconsolidated by pressure at the
bottom. In ice so formed and subjected to such mutations, definite
planes of freezing are, of course, out of the question.
[Sidenote: CONSTITUTION OF GLACIER-ICE.]
The flat round disks and vacuous spots to which I have referred come
here to our aid, and furnish us with an entirely new means of analysing
the internal constitution of a glacier. When we examine a mass of
glacier-ice which contains these disks, we find them lying in all
imaginable planes; not confusedly, however--closer examination shows us
that the disks are arranged in groups, the members of each group being
parallel to a common plane, but the parallelism ceases when different
groups are compared. The effect is exactly what would be observed,
supposing ordinary lake-ice to be broken up, shaken together, and the
confused fragments regelated to a compact continuous mass. In such a
jumble the original planes of freezing would lie in various directions;
but no matter how compact or how transparent ice thus constituted might
appear, a solar beam would at once reveal its internal constitution by
developing the flowers parallel to the planes of freezing of the
respective fragments. A sunbeam sent through glacier-ice always reveals
the flowers in the planes of the disks, so that the latter alone at
once informs us of its crystalline constitution.
[Sidenote: VACUOUS CELLS MISTAKEN FOR AIR-CELLS.]
Hitherto, as I have said, these disks have been mistaken for bubbles
containing air, and their flattening has been ascribed to the pressure
to which they have been subjected. M. Agassiz thus refers to them:--"The
air-bubbles undergo no less curious modifications. In the neighbourhood
of the _névé_, where they are most numerous, those which one sees on the
surface are all spherical or ovoid, but by degrees they begin to be
flattened, and near the end of the glacier there are some that are so
flat _that they might be taken for fissures when seen in profile_. The
drawing represents a piece of ice detached from the gallery of
infiltration. All the bubbles are greatly flattened. But what is most
extraordinary is, that, far from being uniform, _the flattening is
different in each fragment_; so that the bubbles, according to the face
which they offer, appear either very broad or very thin." This
description of glacier-ice is correct: it agrees with the statements of
all other observers. But there are two assumptions in the description
which must henceforth be given up; first, the bubbles seen like fissures
in profile are not air-bubbles at all, but vacuous spots, which the very
constitution of ice renders a necessary concomitant of its inward
melting; secondly, the assumption that the bubbles have been _flattened_
by pressure must be abandoned; for they are found, and may be developed
at will, in lake-ice on which no pressure has been exerted.
[Sidenote: CELLS OF AIR AND WATER.]
But these remarks dispose only of a certain class of cells contained in
glacier-ice. Besides the liquid disks and vacuous spots, there are
innumerable true bubbles entangled in the mass. These have also been
observed and described by M. Agassiz; and Mr. Huxley has also given us
an accurate account of them. M. Agassiz frequently found air and water
associated in the same cell. Mr. Huxley found no exception to the rule:
in each case the bubble of air was enclosed in a cell which was also
partially filled with water. He supposes that the water may be that of
the originally-melted snow which has been carried down from the _névé_
unfrozen. This hypothesis is worthy of a great deal more consideration
than I have had time to give to it, and I state it here in the hope that
it will be duly examined.
My own experience of these associated air and water cells is derived
almost exclusively from lake-ice, in which I have often observed them in
considerable numbers. In examining whether the liquid contents had ever
been frozen or not, I was guided by the following considerations. If the
air be that originally entangled in the solid, it will have the ordinary
atmospheric density at least; but if it be due to the melting of the
walls of the cell, then the water so formed being only eight-ninths of
that of the ice which produced it, _the air of the bubble must be
rarefied_. I suppose I have made a hundred different experiments upon
these bubbles to determine whether the air was rarefied or not, and in
every case found it so. Ice containing the bubbles was immersed in warm
water, and always, when the rigid envelope surrounding a bubble was
melted away, the air suddenly collapsed to a fraction of its original
dimensions. I think I may safely affirm that, in some cases, the
collapse reduced the bubbles to the thousandth part of their original
volume. From these experiments I should undoubtedly infer, that in
lake-ice at least, the liquid of the cells is produced by the melting of
the ice surrounding the bubbles of air.
But I have not subjected the bubbles of glacier-ice to the same
searching examination. I have tried whether the insertion of a pin would
produce the collapse of the bubbles, but it did not appear to do so. I
also made a few experiments at Rosenlaui, with warm water, but the
result was not satisfactory. That ice melts internally at the surfaces
of the bubbles is, I think, rendered certain by my experiments, but
whether the water-cells of glacier-ice are entirely due to such melting,
subsequent observers will no doubt determine.
[Sidenote: "LIQUID LIBERTY."]
I have found these composite bubbles at all parts of glaciers; in the
ice of the moraines, over which a protective covering had been thrown;
in the ice of sand-cones, after the removal of the superincumbent
débris; also in ice taken from the roofs of caverns formed in the
glacier, and which the direct sunlight could hardly by any possibility
attain. That ice should liquefy at the surface of a cavity is, I think,
in conformity with all we know concerning the physical nature of heat.
Regarding it as a motion of the particles, it is easy to see that this
motion is less restrained at the surface of a cavity than in the solid
itself, where the oscillation of each atom is controlled by the
particles which surround it; hence _liquid liberty_, if I may use the
term, is first attained at the surface. Indeed I have proved by
experiment that ice may be melted internally by heat which has been
conducted through its external portions without melting them. These
facts are the exact complements of those of "regelation;" for here, two
moist surfaces of ice being brought into close contact, their liquid
liberty is destroyed and the surfaces freeze together.
THE MOULINS.
(25.)
[Sidenote: MOULIN OF GRINDELWALD GLACIER.]
[Sidenote: DEPTH OF THE SHAFT.]
The first time I had an opportunity of seeing these remarkable
glacier-chimneys was in the summer of 1856, upon the lower glacier of
Grindelwald. Mr. Huxley was my companion at the time, and on crossing
the so-called Eismeer we heard a sound resembling the rumble of distant
thunder, which proceeded from a perpendicular shaft formed in the ice,
and into which a resounding cataract discharged itself. The tube in fact
resembled a vast organ-pipe, whose thunder-notes were awakened by the
concussion of the falling water, instead of by the gentle flow of a
current of air. Beside the shaft our guide hewed steps, on which we
stood in succession, and looked into the tremendous hole. Near the first
shaft was a second and smaller one, the significance of which I did not
then understand; it was not more than 20 feet deep, but seemed filled
with a liquid of exquisite blue, the colour being really due to the
magical shimmer from the walls of the moulin, which was quite empty. As
far as we could see, the large shaft was vertical, but on dropping a
stone into it a shock was soon heard, and after a succession of bumps,
which occupied in all seven seconds, we heard the stone no more. The
depth of the moulin could not be thus ascertained, but we soon found a
second and still larger one which gave us better data. A stone dropped
into this descended without interruption for four seconds, when a
concussion was heard; and three seconds afterwards the final shock was
audible: there was thus but a single interruption in the descent.
Supposing all the acquired velocity to have been destroyed by the shock,
by adding the space passed over by the stone in four and in three
seconds respectively, and making allowance for the time required by the
sound to ascend from the bottom, we find the depth of the shaft to be
about 345 feet. There is, however, no reason to suppose that this
measures the depth of the glacier at the place referred to. These shafts
are to be found in almost all great glaciers; they are very numerous in
the Unteraar Glacier, numbers of them however being empty. On the Mer de
Glace they are always to be found in the region of Trélaporte, one of
the shafts there being, _par excellence_, called the Grand Moulin. Many
of them also occur on the Glacier de Léchaud.
As truly observed by M. Agassiz, these moulins occur only at those parts
of the glacier which are not much rent by fissures, for only at such
portions can the little rills produced by superficial melting collect to
form streams of any magnitude. The valley of unbroken ice formed in the
Mer de Glace near Trélaporte is peculiarly favourable for the collection
of such streams; we see the little rills commencing, and enlarging by
the contributions of others, the trunk-rill pouring its contents into a
little stream which stretches out a hundred similar arms over the
surface of the glacier. Several such streams join, and finally a
considerable brook, which receives the superficial drainage of a large
area, cuts its way through the ice.
[Sidenote: MOULINS EXPLAINED.]
But although this portion of the glacier is free from those
long-continued and permanent strains which, having once rent the ice,
tend subsequently to widen the rent and produce yawning crevasses, it is
not free from local strains sufficient to produce _cracks_ which
penetrate the glacier to a great depth. Imagine such a crack
intersecting such a glacier-rivulet as we have described. The water
rushes down it, and soon scoops a funnel large enough to engulf the
entire stream. The moulin is thus formed, and, as the ice moves
downward, the sides of the crack are squeezed together and regelated,
the seam which marks the line of junction being in most cases distinctly
visible. But as the motion continues, other portions of the glacier come
into the same state of strain as that which produced the first crack; a
second one is formed across the stream, the old shaft is forsaken, and a
new one is hollowed out, in which for a season the cataract plays the
thunderer. I have in some cases counted the forsaken shafts of six old
moulins in advance of an active one. Not far from the Grand Moulin of
the Mer de Glace in 1857 there was a second empty shaft, which evidently
communicated by a subglacial duct with that into which the torrent was
precipitated. Out of the old orifice issued a strong cold blast, the air
being manifestly impelled through the duct by the falling water of the
adjacent moulin.
These shafts are always found in the same locality; the portion of the
Mer de Glace to which I have referred is never without them. Some of the
guides affirm that they are motionless; and a statement of Prof. Forbes
has led to the belief that this was also his opinion.[A] M. Agassiz,
however, observed the motion of some of these shafts upon the glacier of
the Aar; and when on the spot in 1857, I was anxious to decide the point
by accurate measurements with the theodolite.
My friend Mr. Hirst took charge of the instrument, and on the 28th of
July I fixed a single stake beside the Grand Moulin, in a straight line
between a station at Trélaporte and a well-defined mark on the rock at
the opposite side of the valley. On the 31st, the displacement of the
stake amounted to 50 inches, and on the 1st of August it had moved
74-1/2 inches--the moulin, to all appearance, occupying throughout the
same position with regard to the stake. To render this certain,
moreover we subsequently drove two additional stakes into the ice, thus
enclosing the mouth of the shaft in a triangle. On the 8th of August the
displacements were measured and gave the following results:--
Total Motion.
First (old) stake 198 inches.
Second (new) do. 123 "
Third 124 "
[Sidenote: MOTION OF THE MOULINS.]
The old stake had been fixed for 11 days, and its daily motion--_which
was also that of the moulin_--averaged 18 inches a day. Hence the
moulins share the general motion of the glacier, and their apparent
permanence is not, as has been alleged, a proof of the semi-fluidity of
the glacier, but is due to the breaking of the ice as it passes the
place of local strain.
[Sidenote: DEPTH OF "GRAND MOULIN" SOUGHT.]
Wishing to obtain some estimate as to the depth of the ice, Mr. Hirst
undertook the sounding of some of the moulins upon the Glacier de
Léchaud, making use of a tin vessel filled with lumps of lead and iron
as a weight. The cord gave way and he lost his plummet. To measure the
depth of the Grand Moulin, we obtained fresh cord from Chamouni, to
which we attached a four-pound weight. Into a cavity at the bottom of
the weight we stuffed a quantity of butter, to indicate the nature of
the bottom against which the weight might strike. The weight was dropped
into the shaft, and the cord paid out until its slackening informed us
that the weight had come to rest; by shaking the string, however, and
walking round the edge of the shaft, the weight was liberated, and sank
some distance further. The cord partially slackened a second time, but
the strain still remaining was sufficient to render it doubtful whether
it was the weight or the action of the falling water which produced it.
We accordingly paid out the cord to the end, but, on withdrawing it,
found that the greater part of it had been coiled and knotted up by the
falling water. We uncoiled, and sounded again. At a depth of 132 feet
the weight reached a ledge or protuberance of ice, and by shaking and
lifting it, it was caused to descend 31 feet more. A depth of 163 feet
was the utmost we could attain to. We sounded the old moulin to a depth
of 90 feet; while a third little shaft, beside the large one, measured
only 18 feet in depth. We could see the water escape from it through a
lateral canal at its bottom, and doubtless the water of the Grand Moulin
found a similar exit. There was no trace of dirt upon the butter, which
might have indicated that we had reached the bed of the glacier.
FOOTNOTES:
[A] "Every year, and year after year, the watercourses follow the same
lines of direction--their streams are precipitated into the heart of the
glacier by vertical funnels, called 'moulins,' at the very same
points."--Forbes's Fourth Letter upon Glaciers: 'Occ. Pap.,' p. 29.
[Illustration: DIRT-BANDS OF THE MER DE GLACE, AS SEEN FROM A POINT
NEAR THE FLÉGÈRE.
Fig. 35. _To face p. 367._]
DIRT-BANDS OF THE MER DE GLACE.
(26.)
[Sidenote: DIRT-BANDS FROM THE FLEGÈRE.]
These bands were first noticed by Prof. Forbes on the 24th of July,
1842, and were described by him in the following words:--"My eye was
caught by a very peculiar appearance of the surface of the ice, which I
was certain that I now saw for the first time. It consisted of nearly
hyperbolic brownish bands on the glacier, the curves pointing downwards,
and the two branches mingling indiscriminately with the moraines,
presenting an appearance of a succession of waves some hundred feet
apart."[A] From no single point of view hitherto attained can all the
Dirt-Bands of the Mer de Glace be seen at once. To see those on the
terminal portion of the glacier, a station ought to be chosen on the
opposite range of the Brévent, a few hundred yards beyond the Croix de
la Flegère, where we stand exactly in front of the glacier as it issues
into the valley of Chamouni. The appearance of the bands upon the
portion here seen is represented in Fig. 35.
It will be seen that the bands are confined to one side of the glacier,
and either do not exist, or are obliterated by the débris, upon the
other side. The cause of the accumulation of dirt on the right side of
the glacier is, that no less than five moraines are crowded together at
this side. In the upper portions of the Mer de Glace these moraines are
distinct from each other; but in descending, the successive engulfments
and disgorgings of the blocks and dirt have broken up the moraines; and
at the place now before us the materials which composed them are strewn
confusedly on the right side of the glacier. The portion of the ice on
which the dirt-bands appear is derived from the Col du Géant. They do
not quite extend to the end of the glacier, being obliterated by the
dislocation of the ice upon the frozen cascade of Des Bois.
[Sidenote: DIRT-BANDS FROM LES CHARMOZ.]
Let us now proceed across the valley of Chamouni to the Montanvert;
where, climbing the adjacent heights to an elevation of six or eight
hundred feet above the hotel, we command a view of the Mer de Glace,
from Trélaporte almost to the commencement of the Glacier des Bois. It
was from this position that Professor Forbes first observed the bands.
Fifteen, sixteen, and seventeen years later I observed them from the
same position. The number of bands which Professor Forbes counted from
this position was eighteen, with which my observations agree. The entire
series of bands which I observed, with the exception of one or two, must
have been the _successors_ of those observed by Professor Forbes; and my
finding the same number after an interval of so many years proves that
the bands must be due to some regularly recurrent cause. Fig. 36
represents the bands as seen from the heights adjacent to the
Montanvert.
[Illustration: DIRT-BANDS OF THE MER DE GLACE, AS SEEN FROM LES CHARMOZ.
Fig. 36. _To face p. 368._]
I would here direct attention to an analogy between a glacier and a
river, which may be observed from the heights above the Montanvert, but
to which no reference, as far as I know, has hitherto been made. When a
river meets the buttress of a bridge, the water rises against it, and,
on sweeping round it, forms an elevated ridge, between which and the
pier a depression occurs which varies in depth with the force of the
current. This effect is shown by the Mer de Glace on an exaggerated
scale. Sweeping round Trélaporte, the ice pushes itself beyond the
promontory in an elevated ridge, from which it drops by a gradual slope
to the adjacent wall of the valley, thus forming a depression typified
by that already alluded to. A similar effect is observed at the opposite
side of the glacier on turning round the Echelets; and both combine
to form a kind of skew surface. A careful inspection of the
frontispiece will detect this peculiarity in the shape of the glacier.
[Sidenote: FROM THE CLEFT-STATION.]
From neither of the stations referred to do we obtain any clue to the
origin of the dirt-bands. A stiff but pleasant climb will place us in
that singular cleft in the cliffy mountain-ridge which is seen to the
right of the frontispiece; and from it we easily attain the high
platform of rock immediately to the left of it. We stand here high above
the promontory of Trélaporte, and occupy the finest station from which
the Mer de Glace and its tributaries can be viewed. From this station we
trace the dirt-bands over most of the ice that we have already scanned,
and have the further advantage of being able to follow them to their
very source.
This source is the grand ice-cascade which descends in a succession of
precipices from the plateau of the Col du Géant into the valley which
the Glacier du Géant fills. We see from our present point of view that
the bands _are confined to the portion of the glacier which has
descended the cascade_. Fig. 37 represents the bands as seen from the
Cleft-station above Trélaporte.
[Illustration: DIRT-BANDS OF THE MER DE GLACE, AS SEEN FROM THE CLEFT
STATION, TRÉLAPORTE.
Fig. 37. _To face p. 369._]
We are now however at such a height above the glacier and at such a
distance from the base of the cascade, that we can form but an imperfect
notion of the true contour of the surface. Let us therefore descend, and
walk up the Glacier du Géant towards the cascade. At first our road is
level, but we gradually find that at certain intervals we have to ascend
slopes which follow each other in succession, each being separated from
its neighbour by a space of comparatively level ice. The slopes increase
in steepness as we ascend; they are steepest, moreover, on the
right-hand side of the glacier, where it is bounded by that from the
Périades, and at length we are unable to climb them without the aid of
an axe. Soon afterwards the dislocation of the glacier becomes
considerable; we are lost in the clefts and depressions of the ice, and
are unable to obtain a view sufficiently commanding to subdue these
local appearances and convey to us the general aspect. We have at all
events satisfied ourselves as to the existence, on the upper portion of
the glacier, of a succession of undulations which sweep transversely
across it. The term "wrinkles," applied to them by Prof. Forbes, is
highly suggestive of the appearance which they present.
[Sidenote: SNOW-BANDS ON THE GLACIER DU GÉANT.]
From the Cleft-station bands of snow may also be seen partially crossing
the glacier in correspondence with the undulations upon its surface. If
the quantity deposited the winter previous be large, and the heat of
summer not too great, these bands extend quite across the glacier. They
were first observed by Professor Forbes in 1843. In his Fifth Letter is
given an illustrative diagram, which, though erroneous as regards the
position of the veined structure, is quite correct in limiting the
snow-bands to the Glacier du Géant proper.
At the place where the three welded tributaries of the Mer de Glace
squeeze themselves through the strait of Trélaporte, the bands undergo a
considerable modification in shape. Near their origin they sweep across
the Glacier du Géant in gentle curves, with their convexities directed
downwards; but at Trélaporte these curves, the chords of which a short
time previous measured a thousand yards in length, have to squeeze
themselves through a space of four hundred and ninety-five yards wide;
and as might be expected, they are here suddenly sharpened. The apex of
each being thrust forward, they take the form of sharp hyperbolas, and
preserve this character throughout the entire length of the Mer de
Glace.
I would now conduct the reader to a point from which a good general view
of the ice cascade of the Géant is attainable. From the old moraine near
the lake of the Tacul we observe the ice, as it descends the fall, to
be broken into a succession of precipices. It would appear as if the
glacier had its back periodically broken at the summit of the fall, and
formed a series of vast chasms separated from each other by cliffy
ridges of corresponding size. These, as they approach the bottom of the
fall, become more and more toned down by the action of sun and air, and
at some distance below the base of the cascade they are subdued so as to
form the transverse undulations already described. These undulations are
more and more reduced as the glacier descends; and long before the Tacul
is attained, every sensible trace of them has disappeared. The terraces
of the ice-fall are referred to by Professor Forbes in his Thirteenth
Letter, where he thus describes them:--"The ice-falls succeed one
another at regulated intervals, which appear to correspond to the
renewal of each summer's activity in those realms of almost perpetual
frost, when a swifter motion occasions a more rapid and wholesale
projection of the mass over the steep, thus forming curvilinear terraces
like vast stairs, which appear afterwards by consolidation to form the
remarkable protuberant wrinkles on the surface of the Glacier du Géant."
[Sidenote: FORBES'S EXPLANATION.]
With regard to the cause of the distribution of the dirt in bands,
Professor Forbes writes thus in his Third Letter:--"I at length assured
myself that it was entirely owing to the structure of the ice, which
retains the dirt diffused by avalanches and the weather on those parts
which are most porous, whilst the compacter portion is washed clean by
the rain, so that those bands are nothing more than visible traces of
the direction of the internal icy structure." Professor Forbes's theory,
at that time, was that the glacier is composed throughout of a series of
alternate segments of hard and porous ice, in the latter of which the
dirt found a lodgment. I do not know whether he now retains his first
opinion; but in his Fifteenth Letter he speaks of accounting for "the
less compact structure of the ice beneath the dirt-band."
It appears to me that in the above explanation cause has been mistaken
for effect. The ice on which the dirt-bands rest certainly appears to be
of a spongier character than the cleaner intermediate ice; but instead
of this being the cause of the dirt-bands, the latter, I imagine, by
their more copious absorption of the sun's rays and the consequent
greater disintegration of the ice, are the cause of the apparent
porosity. I have not been able to detect any relative porosity in the
"internal icy structure," nor am I able to find in the writings of
Professor Forbes a description of the experiments whereby he satisfied
himself that this assumed difference exists.
[Sidenote: TRANSVERSE UNDULATIONS.]
[Sidenote: INFLUENCE OF DIRECTION OF GLACIER.]
Several days of the summer of 1857 were devoted by me to the examination
of these bands. I then found the bases and the frontal slopes of the
undulations to which I have referred covered with a fine brown mud.
These slopes were also, in some cases, covered with snow which the great
heat of the weather had not been able entirely to remove. At places
where the residue of snow was small its surface was exceedingly
dirty--so dirty indeed that it appeared as if peat-mould had been strewn
over it; its edges particularly were of a black brown. It was perfectly
manifest that this snow formed a receptacle for the fine dirt
transported by the innumerable little rills which trickled over the
glacier. The snow gradually wasted, but it left its sediment behind, and
thus each of the snowy bands observed by Professor Forbes in 1843,
contributed to produce an appearance perfectly antithetical to its own.
I have said that the frontal slopes of the undulations were thus
covered; and it was on these, and not in the depressions, that the snow
principally rested. The reason of this is to be found in the _bearing_
of the Glacier du Géant, which, looking downwards, is about fourteen
degrees east of the meridian.[B] Hence the frontal slopes of the
undulations have a _northern aspect_, and it is this circumstance which,
in my opinion, causes the retention of the snow upon them. Irrespective
of the snow, the mere tendency of the dirt to accumulate at the bases of
the undulations would also produce bands, and indeed does so on many
glaciers; but the precision and beauty of the dirt-bands of the Mer de
Glace are, I think, to be mainly referred to the interception by the
snow of the fine dark mud before referred to on the northern slopes of
its undulations.
[Sidenote: BANDS DO NOT CROSS MORAINES.]
Were the statements of some writers upon this subject well founded, or
were the dirt-bands as drawn upon the map of Professor Forbes correctly
shown, this explanation could not stand a moment. It has been urged that
the dirt-bands cannot thus belong to a single tributary of the Mer de
Glace; for if they did, they would be confined to that tributary upon
the trunk-glacier; whereas the fact is that they extend quite across the
trunk, and intersect the moraines which divide the Glacier du Géant from
its fellow-tributaries. From my first acquaintance with the Mer de Glace
I had reason to believe that this statement was incorrect; but last year
I climbed a third time to the Cleft-station for the purpose of once more
inspecting the bands from this fine position. I was accompanied by Dr.
Frankland and Auguste Balmat, and I drew the attention of both
particularly to this point. Neither of them could discern, nor could I,
the slightest trace of a dirt-band crossing any one of the moraines.
Upon the trunk-stream they were just as much confined to the Glacier du
Géant as ever. If the bands even existed east of the moraines, they
could not be seen, the dirt on this part of the glacier being sufficient
to mask them.
The following interesting fact may perhaps have contributed to the
production of the error referred to. Opposite to Trélaporte the eastern
arms of the dirt-bands run so obliquely into the moraine of La Noire
that the latter appears to be a tangent to them. But this moraine runs
along the Mer de Glace, not far from its centre, and consequently the
point of contact of each dirt-band with the moraine moves more quickly
than the point of contact of the western arm of the same band with the
side of the valley. Hence there is a tendency to _straighten_ the bands;
and at some distance down the glacier the effect of this is seen in the
bands abutting against the moraine of La Noire at a larger angle than
before. The branches thus abutting have, I believe, been ideally
prolonged across the moraines.
[Illustration: Fig. 38. Plan of Dirt-bands taken from Johnson's
'Physical Atlas.']
On the map published by Prof. Forbes in 1843 the bands are shown
crossing the medial moraines of the Mer de Glace; and they are also thus
drawn on the map in Johnson's 'Physical Atlas' published in 1849. The
text is also in accordance with the map:--"Opposite to the Montanvert,
and beyond les Echelets, the curved loops (dirt-bands) extend _across
the entire glacier_. They are single, and therefore _cut_ the medial
moraine, though at a very slight angle."--'Travels,' p. 166. The italics
here belong to Prof. Forbes. In order to help future observers to place
this point beyond doubt, I annex, in Fig. 38, a portion of the map of
the Mer de Glace taken from the Atlas referred to. If it be compared
with Fig. 35 the difference between Prof. Forbes and myself will be
clearly seen. The portion of the glacier represented in both diagrams
may be viewed from the point near the Flegère already referred to.
[Sidenote: ANNUAL "RINGS."]
The explanation which I have given involves three considerations:--The
transverse breaking of the glacier on the cascade, and the gradual
accumulation of the dirt in the hollows between the ridges; the
subsequent toning down of the ridges to gentle protuberances which sweep
across the glacier; and the collection of the dirt upon the slopes and
at the bases of these protuberances. Whether the periods of transverse
fracture are annual or not--whether the "wrinkles" correspond to a
yearly gush--and whether, consequently, the dirt-bands mark the growth
of a glacier as the "annual rings" mark the growth of a tree, I do not
know. It is a conjecture well worthy of consideration; but it is only a
conjecture, which future observation may either ratify or refute.
FOOTNOTES:
[A] 'Travels,' page 162.
[B] In the large map of Professor Forbes the bearing of the valley is
nearly sixty degrees west of the meridian; but this is caused by the
true north being drawn on the wrong side of the magnetic north; thus
making the declination easterly instead of westerly. In the map in
Johnson's 'Physical Atlas' this mistake is corrected.
THE VEINED STRUCTURE OF GLACIERS.
(27.)
[Sidenote: GENERAL APPEARANCE.]
The general appearance of the veined structure may be thus briefly
described:--The ice of glaciers, especially midway between their
mountain-sources and their inferior extremities, is of a whitish hue,
caused by the number of small air-bubbles which it contains, and which,
no doubt, constitute the residue of the air originally entrapped in the
interstices of the snow from which it has been derived. Through the
general whitish mass, at some places, innumerable parallel veins of
clearer ice are drawn, which usually present a beautiful blue colour,
and give the ice a laminated appearance. The cause of the blueness is,
that the air-bubbles, distributed so plentifully through the general
mass, do not exist in the veins, or only in comparatively small numbers.
In different glaciers, and in different parts of the same glacier, these
veins display various degrees of perfection. On the clean unweathered
walls of some crevasses, and in the channels worn in the ice by
glacier-streams, they are most distinctly seen, and are often
exquisitely beautiful. They are not to be regarded as a partial
phenomenon, or as affecting the constitution of glaciers to a small
extent merely. A large portion of the ice of some glaciers is thus
affected. The greater part, for example, of the Mer de Glace consists of
this laminated ice; and the whole of the Glacier of the Rhone, from the
base of the ice-cascade downwards, is composed of ice of the same
description.
[Sidenote: GROOVES ON THE SURFACE OF GLACIERS.]
Those who have ascended Snowdon, or wandered among the hills of
Cumberland, or even walked in the environs of Leeds, Blackburn, and
other towns in Yorkshire and Lancashire, where the stratified sandstone
of the district is used for building purposes, may have observed the
weathered edges of the slate rocks or of the building-stone to be
grooved and furrowed. Some laminæ of such rocks withstand the action of
the atmosphere better than others, and the more resistant ones stand out
in ridges after the softer parts between them have been eaten away. An
effect exactly similar is observed where the laminated ice of glaciers
is exposed to the action of the sun and air. Little grooves and ridges
are formed upon its surface, the more resistant plates protruding after
the softer material between them has been melted away.
One consequence of this furrowing is, that the light dirt scattered by
the winds over the surface of the glacier is gradually washed into the
little grooves, thus forming fine lines resembling those produced by the
passage of a rake over a sanded walk. These lines are a valuable index
to some of the phenomena of motion. From a position on the ice of the
Glacier du Géant a little higher up than Trélaporte a fine view of these
superficial groovings is obtained; but the dirt-lines are not always
straight. A slight power of independent motion is enjoyed by the
separate parts into which a glacier is divided by its crevasses and
dislocations, and hence it is, that, at the place alluded to, the
dirt-lines are bent hither and thither, though the ruptures of
continuity are too small to affect materially the general direction of
the structure. On the glacier of the Talèfre I found these groovings
useful as indicating the character of the forces to which the ice near
the summit of the fall is subjected. The ridges between the chasms are
in many cases violently bent and twisted, while the adjacent groovings
enable us to see the normal position of the mass.
[Sidenote: GUYOT'S OBSERVATIONS.]
The veined structure has been observed by different travellers; but it
was probably first referred to by Sir David Brewster, who noticed the
veins of the Mer de Glace on the 10th of September, 1814. It was also
observed by General Sabine,[A] by Rendu, by Agassiz, and no doubt by
many others; but the first clear description of it was given by M.
Guyot, in a communication presented to the Geological Society of France
in 1838. I quote the following passage from this paper:--"I saw under my
feet the surface of the entire glacier covered with regular furrows from
one to two inches wide, hollowed out in a half snowy mass, and separated
by protruding plates of harder and more transparent ice. It was evident
that the mass of the glacier here was composed of two sorts of ice, one
that of the furrows, snowy and more easily melted; the other that of the
plates, more perfect, crystalline, glassy, and resistant; and that the
unequal resistance which the two kinds of ice presented to the
atmosphere was the cause of the furrows and ridges. After having
followed them for several hundreds of yards, I reached a fissure twenty
or thirty feet wide, which, as it cut the plates and furrows at right
angles, exposed the interior of the glacier to a depth of thirty or
forty feet, and gave a beautiful transverse section of the structure. As
far as my vision could reach I saw the mass of the glacier composed of
layers of snowy ice, each two of which were separated by one of the
plates of which I have spoken, the whole forming a regularly laminated
mass, which resembled certain calcareous slates."
[Sidenote: FORBES'S RESEARCHES.]
Previous observers had mistaken the lamination for stratification; but
M. Guyot not only clearly saw that they were different, but in the
comparison which he makes he touches, I believe, on the true cause of
the glacier-structure. He did not hazard an explanation of the
phenomenon, and I believe his memoir remained unprinted. In 1841 the
structure was noticed by Professor Forbes during his visit to M. Agassiz
on the lower Aar Glacier, and described in a communication presented by
him to the Royal Society of Edinburgh. He subsequently devoted much time
to the subject, and his great merit in connexion with it consists in the
significance which he ascribed to the phenomenon when he first observed
it, and in the fact of his having proved it to be a constitutional
feature of glaciers in general.
[Sidenote: FORBES'S THEORY.]
The first explanation given of those veins by Professor Forbes was, that
they were small fissures formed in the ice by its motion; that these
were filled with the water of the melted ice in summer, which froze in
winter so as to form the blue veins. This is the explanation given in
his 'Travels,' page 377; and in a letter published in the 'Edinburgh New
Philosophical Journal,' October, 1844, it is re-affirmed in these
words:--"With the abundance of blue bands before us in the direction in
which the differential motion must take place (in this case sensibly
parallel to the sides of the glacier), it is impossible to doubt that
these infiltrated crevices (for such they undoubtedly are) have this
origin." This theory was examined by Mr. Huxley and myself in our joint
paper; but it has been since alleged that ours was unnecessary labour,
Prof. Forbes himself having in his Thirteenth Letter renounced the
theory, and substituted another in its place. The latter theory differs,
so far as I can understand it, from the former in this particular, that
the _freezing of the water_ in the fissures is discarded, their sides
being now supposed to be united "by the simple effects of time and
cohesion."[B] For a statement of the change which his opinions have
undergone, I would refer to the Prefatory Note which precedes the volume
of 'Occasional Papers' recently published by Prof. Forbes; but it would
have diminished my difficulty had the author given, in connexion with
his new volume, a more distinct statement of his present views regarding
the veined structure. With many of his observations and remarks I should
agree; with many others I cannot say whether I agree or not; and there
are others still with which I do not think I should agree: but in hardly
any case am I certain of his precise views, excepting, indeed, the
cardinal one, wherein he and others agree in ascribing to the structure
a different origin from stratification. Thus circumstanced, my proper
course, I think, will be to state what I believe to be the cause of the
structure, and leave it to the reader to decide how far our views
harmonize; or to what extent either of them is a true interpretation of
nature.
[Sidenote: USUAL ASPECT OF BLUE VEINS.]
Most of the earlier observers considered the structure to be due to the
stratification of the mountain-snows--a view which has received later
development at the hands of Mr. John Ball; and the practical difficulty
of distinguishing the undoubted effects of _stratification_ from the
phenomena presented by _structure_, entitles this view to the fullest
consideration. The blue veins of glaciers are, however, not always, nor
even generally, such as we should expect to result from stratification.
The latter would furnish us with distinct planes extending parallel to
each other for considerable distances through the glacier; but this,
though sometimes the case, is by no means the general character of the
structure. We observe blue streaks, from a few inches to several feet in
length, upon the walls of the same crevasse, and varying from the
fraction of an inch to several inches in thickness. In some cases the
streaks are definitely bounded, giving rise to an appearance resembling
the section of a lens, and hence called the "lenticular structure" by
Mr. Huxley and myself; but more usually they fade away in pale washy
streaks through the general mass of the whitish ice. In Fig. 39 I have
given a representation of the structure as it is very commonly exhibited
on the walls of crevasses. Its aspect is not that which we should expect
from the consolidation of successive beds of mountain snow.
[Illustration: Fig. 39. Veined Structure of the walls of crevasses.]
Further, at the bases of ice-cascades the structural laminæ are usually
_vertical_: below the cascade of the Talèfre, of the Noire, of the
Strahleck branch of the Lower Grindelwald Glacier, of the Rhone, and
other ice-falls, this is the case; and it seems extremely difficult to
conceive that a mass horizontally stratified at the summit of the fall,
should, in its descent, contrive to turn its strata perfectly on end.
Again, we often find a very feebly-developed structure at the central
portions of a glacier, while the lateral portions are very decidedly
laminated. This is the case where the inclination of the glacier is
nearly uniform throughout; and where no medial moraines occur to
complicate the phenomenon. But if the veins mark the bedding, there
seems to be no sufficient reason for their appearance at the lateral
portions of the glacier, and their absence from the centre.
[Sidenote: ILLUSTRATIVE EXPERIMENTS.]
This leads me to the point at which what I consider to be the true cause
of the structure may be referred to. The theoretic researches of Mr.
Hopkins have taught us a good deal regarding the pressures and tensions
consequent upon glacier-motion. Aided by this knowledge, and also by a
mode of experiment first introduced by Professor Forbes, I will now
endeavour to explain the significance of the fact referred to in the
last paragraph. If a plastic substance, such as mud, flow down a sloping
canal, the lateral portions, being held back by friction, will be
outstripped by the central ones. When the flow is so regulated that the
velocity of a point at the centre shall not vary throughout the entire
length of the canal, a coloured circle stamped upon the centre of the
mud stream, near its origin, will move along with the mud, and still
retain its circular form; for, inasmuch as the velocity of all points
along the centre is the same, there can be no elongation of the circle
longitudinally or transversely by either strain or pressure. A similar
absence of longitudinal pressure may exist in a glacier, and, where it
exists throughout, no central structure can, in my opinion, be
developed.
But let a circle be stamped upon the mud-stream near its side, then,
when the mud flows, this circle will be distorted to an oval, with its
major axis oblique to the direction of motion; the cause of this is that
the portion of the circle farthest from the side of the canal moves
more freely than that adjacent to the side. The mechanical effect of the
slower lateral motion is to squeeze the circle in one direction, and
draw it out in the perpendicular one.
[Sidenote: MARGINAL STRUCTURE.]
[Illustration: Fig. 40. Figure explanatory of the Marginal Structure.]
A glance at Fig. 40 will render all that I have said intelligible. The
three circles are first stamped on the mud in the same transverse line;
but after they have moved downwards they will be in the same straight
line no longer. The central one will be the foremost; while the lateral
ones have their forms changed from circles to ovals. In a glacier of the
shape of this canal exactly similar effects are produced. Now the
shorter axis _m n_ of each oval is a line of squeezing or pressure; the
longer axis is a line of strain or tension; and the associated
glacier-phenomena are as follows:--Across the line _m n_, or
perpendicular to the pressure, we have the _veined structure_ developed,
while across the line of tension the glacier usually breaks and forms
_marginal crevasses_. Mr. Hopkins has shown that the lines of greatest
pressure and of greatest strain are at right angles to each other, and
that in valleys of a uniform width they enclose an angle of forty-five
degrees with the side of the glacier. To the structure thus formed I
have applied the term _marginal structure_. Here, then, we see that
there are mechanical agencies at work near the side of such a glacier
which are absent from the centre, and we have effects developed--I
believe _by the pressure_--in the lateral ice, which are not produced in
the central.
I have used the term "uniform inclination" in connexion with the
marginal structure, and my reason for doing so will now appear. In many
glaciers the structure, instead of being confined to the margins,
sweeps quite across them. This is the case, for example, on the Glacier
du Géant, the structure of which is prolonged into the Mer de Glace. In
passing the strait at Trélaporte, however, the curves are squeezed and
their apices bruised, so that the structure is thrown into a state of
confusion; and thus upon the Mer de Glace we encounter difficulty in
tracing it fairly from side to side. Now the key to this transverse
structure I believe to be the following: Where the inclination of the
glacier suddenly changes from a steep slope to a gentler, as at the
bases of the "cascades,"--the ice to a certain depth must be thrown into
a state of violent longitudinal compression; and along with this we have
the resistance which the gentler slope throws athwart the ice descending
from the steep one. At such places a structure is developed transverse
to the axis of the glacier, and likewise transverse to the pressure. The
quicker flow of the centre causes this structure to bend more and more,
and after a time it sweeps in vast curves across the entire glacier.
[Sidenote: STRUCTURE OF GRINDELWALD GLACIER.]
In illustration of this point I will refer, in the first place, to that
tributary of the Lower Glacier of Grindelwald which descends from the
Strahleck. Walking up this tributary we come at length to the base of an
ice-fall. Let the observer here leave the ice, and betake himself to
either side of the flanking mountain. On attaining a point which
commands a view both of the fall and of the glacier below it, an
inspection of the glacier will, I imagine, solve to his satisfaction the
case of structure now under consideration.
It is indeed a grand experiment which Nature here submits to our
inspection. The glacier descending from its _névé_ reaches the summit of
the cascade, and is broken transversely as it crosses the brow; it
afterwards descends the fall in a succession of cliffy ice-ridges with
transverse hollows between them. In these latter the broken ice and
débris collect, thus partially choking the fissures formed in the first
instance. Carrying the eye downwards along the fall, we see, as we
approach the base, these sharp ridges toned down; and a little below the
base they dwindle into rounded protuberances which sweep in curves quite
across the glacier. At the base of the fall the structure begins to
appear, feebly at first, but becoming gradually more pronounced, until,
at a short distance below the base of the fall, the eye can follow the
fine superficial groovings from side to side; while at the same time the
ice underneath the surface has become laminated in the most beautiful
manner.
It is difficult to convey by writing the force of the evidence which the
actual observation of this natural experiment places before the mind.
The ice at the base of the fall, retarded by the gentler inclination of
the valley, has to bear the thrust of the descending mass, the sudden
change of inclination producing powerful longitudinal compression. The
protuberances are squeezed more closely together, the hollows between
them appear to wrinkle up in submission to the pressure--in short, the
entire aspect of the glacier suggests the powerful operations of the
latter force. At the place where _it_ is exerted the veined structure
makes its appearance; and being once formed, it moves downwards, and
gives a character to other portions of the glacier which had no share in
its formation.
[Sidenote: BASE OF CASCADE A "STRUCTURE-MILL."]
An illustration almost as good, and equally accessible, is furnished by
the Glacier of the Rhone. I have examined the grand cascade of this
glacier from both sides; and an ordinary mountaineer will find little
difficulty in reaching a point from which the fall and the terminal
portion of the glacier are both distinctly visible. Here also he will
find the cliffy ridges separated from each other by transverse chasms,
becoming more and more subdued at the bottom of the fall, and
disappearing entirely lower down the glacier. As in the case of the
Grindelwald Glacier the squeezing of the protuberances and of the spaces
between them, is quite apparent, and where this squeezing commences the
transverse structure makes its appearance. All the ice that forms the
lower portion of this glacier has to pass through the _structure-mill_
at the bottom of the fall, and the consequence is that _it is all
laminated_.
[Sidenote: STRUCTURE OF RHONE GLACIER.]
[Illustration: Fig. 41. Plan of part of ice-fall, and of glacier below
it (Glacier of the Rhone).]
[Illustration: Fig. 42. Section of part of ice-fall, and of glacier
below it (Glacier of the Rhone).]
[Sidenote: TRANSVERSE STRUCTURE.]
This case of structural development will be better appreciated on
reference to Figs. 41 and 42, the former of which is a plan, and the
latter a section, of a part of the ice-fall and of the glacier below it;
_a b e f_ is the gorge of the fall, _f b_ being the base. The transverse
cliffy ice-ridges are shown crossing the cascade, being subdued at the
base to protuberances which gradually disappear as they advance
downwards. The structure sweeps over the glacier in the direction of the
fine curved lines; and I have also endeavoured to show the direction of
the radial crevasses, which, in the centre at least, are at right angles
to the veins. To the manifestation of structure here considered I have,
for the sake of convenient reference, applied the term _transverse
structure_.
A third exhibition of the structure is now to be noticed. We sometimes
find it in the _middle_ of a glacier and running _parallel_ to its
length. On the centre of the ice-fall of the Talèfre, for example, we
have a structure of this kind which preserves itself parallel to the
axis of the fall from top to bottom. But we discover its origin higher
up. The structure here has been produced at the extremity of the Jardin,
where the divided ice meets, and not only brings into partial
parallelism the veins previously existing along the sides of the Jardin,
but develops them still further by the mutual pressure of the portions
of newly welded ice. Where two tributary glaciers unite, this is perhaps
without exception the case. Underneath the moraine formed by the
junction of the Talèfre and Léchaud the structure is finely developed,
and the veins run in the direction of the moraine. The same is true of
the ice under the moraine formed by the junction of the Léchaud and
Géant. These afterwards form the great medial moraines of the Mer de
Glace, and hence the structure of the trunk-stream underneath these
moraines is parallel to the direction of the glacier. This is also true
of the system of moraines formed by the glaciers of Monte Rosa. It is
true in an especial manner of the lower glacier of the Aar, whose
medial moraine perhaps attains grander proportions than any other in the
Alps, and underneath which the structure is finely developed.
[Sidenote: LONGITUDINAL STRUCTURE.]
[Illustration: Fig. 43. Figure explanatory of Longitudinal Structure.]
The manner in which I have illustrated the production of this structure
will be understood from Fig. 43. B B are two wooden boxes, communicating
by sluice-fronts with two branch canals, which unite to a common trunk
at G. They are intended to represent respectively the trunk and
tributaries of the Unteraar Glacier, the part G being the Abschwung,
where the Lauteraar and Finsteraar glaciers unite to form the Unteraar.
The mud is first permitted to flow beneath the two sluices until it has
covered the bottom of the trough for some distance, when it is arrested.
The end of a glass tube is then dipped into a mixture of rouge and
water, and small circles are stamped upon the mud. The two branches are
thickly covered with these circles. The sluices being again raised, the
mud in the branches moves downwards, carrying with it the circles
stamped upon it; and the manner in which these circles are distorted
enables us to infer the strains and pressures to which the mud is
subjected during its descent. The figure represents approximately what
takes place. The side-circles, as might be expected, are squeezed to
oblique ovals, but it is at the junction of the branches that the chief
effect of pressure is produced. Here, by the mutual thrust of the
branches, the circles are not only changed to elongated ellipses, but
even squeezed to straight lines. In the case of the glacier this is the
region at which the structure receives its main development. To this
manifestation of the veins I have applied the term _longitudinal
structure_.
The three main sources of the blue veins are, I think, here noted; but
besides these there are many local causes which influence their
production. I have seen them well formed where a glacier is opposed by
the sudden bend of a valley, or by a local promontory which presents an
obstacle sufficient to bring the requisite pressure into play. In the
glaciers of the Tyrol and of the Oberland I have seen examples of this
kind; but the three principal sources of the veins are, I think, those
stated above.
[Sidenote: EFFORTS TO SOLVE QUESTION.]
It was long before I cleared my mind of doubt regarding the origin of
the lamination. When on the Mer de Glace in 1857 I spared neither risk
nor labour to instruct myself regarding it. I explored the Talèfre
basin, its cascade, and the ice beneath it. Several days were spent amid
the ice humps and cliffs at the lower portion of the fall. I suppose I
traversed the Glacier du Géant twenty times, and passed eight or ten
days amid the confusion of its great cascade. I visited those places
where, it had been affirmed, the veins were produced. I endeavoured to
satisfy myself of the mutability which had been ascribed to them; but a
close examination reduced the value of each particular case so much that
I quitted the glacier that year with nothing more than an _opinion_ that
the structure and the stratification were two different things. I,
however, drew up a statement of the facts observed, with the view of
presenting it to the Royal Society; but I afterwards felt that in thus
acting I should merely swell the literature of the subject without
adding anything certain. I therefore withheld the paper, and resolved
to devote another year to a search among the chief glaciers of the
Oberland, of the Canton Valais, and of Savoy, for proofs which should
relieve my mind of all doubt upon the subject.
[Sidenote: EXPEDITION FOR THIS PURPOSE.]
Accordingly in 1858 I visited the glaciers of Rosenlaui, Schwartzwald,
Grindelwald, the Aar, the Rhone, and the Aletsch, to the examination of
which latter I devoted more than a week. I afterwards went to Zermatt,
and, taking up my quarters at the Riffelberg, devoted eleven days to the
examination of the great system of glaciers of Monte Rosa. I explored
the Görner Glacier up almost to the Cima de Jazzi; and believed that in
it I could trace the structure from portions of the glacier where it
vanished, through various stages of perfection, up to its full
development. I believe this still; but yet it is nothing but a belief,
which the utmost labour that I could bestow did not raise to a
certainty. The Western glacier of Monte Rosa, the Schwartze Glacier, the
Trifti Glacier, the glacier of the little Mont Cervin, and of St.
Théodule, were all examined in connexion with the great trunk-stream of
the Görner, to which they weld themselves; and though the more I pursued
the subject the stronger my conviction became that pressure was the
cause of the structure, a crucial case was still wanting.
In the phenomena of slaty cleavage, it is often, if not usually, found
that the true cleavage _cuts_ the planes of stratification--sometimes at
a very high angle. Had this not been proved by the observations of
Sedgwick and others, geologists would not have been able to conclude
that cleavage and bedding were two different things, and needed wholly
different explanations. My aim, throughout the expedition of 1858, was
to discover in the ice a parallel case to the above; to find a clear and
undoubted instance where the veins and the stratification were
simultaneously exhibited, cutting each other at an unmistakable angle.
On the 6th of August, while engaged with Professor Ramsay upon the
Great Aletsch Glacier, not far from its junction with the Middle
Aletsch, I observed what appeared to me to be the lines of bedding
running nearly horizontal along the wall of a great crevasse, while
cutting them at a large angle was the true veined structure. I drew my
friend's attention to the fact, and to him it appeared perfectly
conclusive. It is from a sketch made by him at the place that Fig. 44
has been taken.
[Sidenote: CASE OF STRUCTURE ON THE ALETSCH.]
[Illustration: Fig. 44. Structure and bedding on the Great Aletsch
Glacier.]
This was the only case of the kind which I observed upon the Aletsch
Glacier; and as I afterwards spent day after day upon the Monte Rosa
glaciers, vainly seeking a similar instance, the thought again haunted
me that we might have been mistaken upon the Aletsch. In this state of
mind I remained until the 18th of August, a day devoted to the
examination of the Furgge Glacier, which lies at the base of the Mont
Cervin.
[Sidenote: STRUCTURE OF THE FURGGE GLACIER.]
Crossing the valley of the Görner Glacier, and taking a plunge as I
passed into the Schwarze See, I reached, in good time, the object of my
day's excursion. Walking up the glacier, I at length found myself
opposed by a frozen cascade composed of four high terraces of ice. The
highest of these was chiefly composed of ice-cliffs and _séracs_, many
of which had fallen, and now stood like rocking-stones upon the edge of
the second terrace. The glacier at the base of the cascade was strewn
with broken ice, and some blocks two hundred cubic feet in volume had
been cast to a considerable distance down the glacier.
Upon the faces of the terraces the stratification of the _névé_ was most
beautifully shown, running in parallel and horizontal lines along the
weathered surface. The snow-field above the cascade is a frozen plain,
smooth almost as a sheltered lake. The successive snow-falls deposit
themselves with great regularity, and at the summit of the cascade the
sections of the _névé_ are for the first time exposed. Hence their
peculiar beauty and definition.
[Sidenote: ICE TERRACE EXAMINED.]
Indeed the figure of a lake pouring itself over a rocky barrier which
curves convexly upwards, thus causing the water to fall down it, not
only longitudinally over the vertex of the curve, but laterally over its
two arms, will convey a tolerably correct conception of the shape of the
fall. Towards the centre the ice was powerfully squeezed laterally, the
beds were bent, and their continuity often broken by faults. On
inspecting the ice from a distance with my opera glass, I thought I saw
structural groovings cutting the strata at almost a right angle. Had the
question been an undisputed one, I should perhaps have felt so sure of
this as not to incur the danger of pushing the inquiry further; but,
under the circumstances, danger was a secondary point. Resigning,
therefore, my glass to my guide, who was to watch the tottering blocks
overhead, and give me warning should they move, I advanced to the base
of the fall, removed with my hatchet the weathered surface of the ice,
and found underneath it the true veined structure, cutting, at nearly a
right angle, the planes of stratification. The superficial groovings
were not uniformly distributed over the fall, but appeared most decided
at those places where the ice appeared to have been most squeezed. I
examined three or four of these places, and in each case found the true
veins nearly vertical, while the bedding was horizontal. Having
perfectly satisfied myself of these facts, I made a speedy retreat, for
the ice-blocks seemed most threatening, and the sunny hour was that at
which they fall most frequently.
I next tried the ascent of the glacier up a dislocated declivity to the
right. The ice was much riven, but still practicable. My way for a time
lay amid fissures which exposed magnificent sections, and every step I
took added further demonstration to what I had observed below. The
strata were perfectly distinct, the structure equally so, and one
crossed the other at an angle of seventy or eighty degrees. Mr. Sorby
has adduced a case of the crumpling of a bed of sandstone through which
the cleavage passes: here on the glacier I had parallel cases; the beds
were bent and crumpled, but the structure ran through the ice in sharp
straight lines. This perhaps was the most pleasant day I ever spent upon
the glaciers: my mind was relieved of a long brooding doubt, and the
intellectual freedom thus obtained added a subjective grandeur to the
noble scene before me. Climbing the cliffs near the base of the
Matterhorn, I walked along the rocky spine which extends to the Hörnli,
and afterwards descended by the valley of Zmutt to Zermatt.
A year after my return to England a remark contained in Professor
Mousson's interesting little work 'Die Gletscher der Jetzzeit' caused me
to refer to the atlas of M. Agassiz's 'Système Glaciaire,' from which I
learned that this indefatigable observer had figured a case of
stratification and structure cutting each other. If, however, I had seen
this figure beforehand, it would not have changed my movements; for the
case, as sketched, would not have convinced me. I have now no doubt that
M. Agassiz has preceded me in this observation, and hence my results
are to be taken as mere confirmations of his.
[Sidenote: LAMINATION AND STRATIFICATION.]
Fig. 45 represents a crumpled portion of the ice with the lines of
lamination passing through the strata. Fig. 46 represents a case where a
fault had occurred, the veins at both sides of the line of dislocation
being inclined towards each other.
[Illustration: Fig. 45. Structure and Stratification on the Furgge
glacier.]
[Illustration: Fig. 46. Structure and Stratification on the Furgge
glacier.]
[Figs. 45 and 46 are from sketches made on the Furgge Glacier.--L. C.
T.]
FOOTNOTES:
[A] In reply to a question in connexion with this subject, General
Sabine has favoured me with the following note:--
"My dear Tyndall,
"It was in the summer of 1841, at the Lower Grindelwald
Glacier, that I first saw, and was greatly impressed and
interested by examining and endeavouring to understand (in
which I did not succeed), the veined structure of the ice. I do
not remember when I mentioned it to Forbes, but it must be
before 1843, because it is noticed in his book, p. 29. I had
never observed it in the glaciers of Spitzbergen or Baffin's
Bay, or in the icebergs of the shores and straits of Davis or
Barrow. I feel the more confident of this, because, when I
first saw the veined structure in Switzerland, my Arctic
experience was more fresh in my recollection, and I recollected
nothing like it.
"_Veins_ are indeed not uncommon in icebergs, but they quite
resemble veins in rocks, and are formed by water filling
fissures and freezing into blue ice, finely contrasted with the
white granular substance of the berg.
"The ice of the Grindelwald Glacier (where I examined the
veined structure) was broken up into very large masses, which
by pressure had been upturned, so that a very poor judgment
would be formed of the direction of the veins as they existed
in the glacier before it had broken up.
"Sincerely yours,
"EDWARD SABINE.
"_Feb. 20, 1860_."
[B] In a letter to myself, published in the 17th volume of the
'Philosophical Magazine,' Professor Forbes writes as follows:--"In 1846,
then, I abandoned no part of the theory of the veined structure, on
which as you say so much labour had been expended, except the admission,
always yielded with reluctance, and got rid of with satisfaction, that
the congelation of water in the crevices of the glacier may extend in
winter to a great depth."
THE VEINED STRUCTURE AND THE DIFFERENTIAL MOTION.
(28.)
[Sidenote: DIFFERENTIAL MOTION GREATEST AT EDGES.]
I have now to examine briefly the explanation of the structure which
refers it to differential motion--to a sliding of the particles of ice
past each other, which leaves the traces of its existence in the blue
veins. The fact is emphatically dwelt upon by those who hold this view,
that the structure is best developed nearest to the sides of the
glacier, where the differential motion is greatest. Why the differential
motion is at its maximum near to the sides is easily understood. Let A
B, C D, Fig. 47, represent the two sides of a glacier, moving in the
direction of the arrow, and let _m a b c n_ be a straight line of stakes
set out across the glacier to-day. Six months hence this line, by the
motion of the ice downwards, will be bent to the form _m a' b' c' n_:
this curve will not be circular, it will be flattened in the middle; the
points _a_ and _c_, at some distance on each side of the centre _b_,
move in fact with nearly the same velocity as the centre itself. Not so
with the sides:--_a'_ and _c'_ have moved considerably in advance of _m_
and _n_, and hence we say that the difference of motion, or the
differential motion, of the particles of ice near to the side is a
maximum.
[Illustration: Fig. 47. Diagram illustrating Differential Motion.]
During all this time the points _m a' b' c' n_ have been moving straight
down the glacier; and hence it will be understood that the sliding of
the parts past each other, or, in other words, the differential motion,
_is parallel to the sides of the glacier_. This, indeed, is the only
differential motion that experiment has ever established; and
consequently, when we find the best blue veins referred to the sides of
the glacier because the differential motion is there greatest, we
naturally infer that the motion meant is parallel to the sides.
[Sidenote: STRUCTURE OBLIQUE TO SIDES.]
But the fact is, that this motion would not at all account for the blue
veins, for they are not parallel to the sides, but _oblique_ to them.
This difficulty revealed itself after a time to those who first
propounded the theory of differential motion, and caused them to modify
their explanation of the structure. Differential motion is still assumed
to be the cause of the veins, but now a motion is meant oblique to the
sides, and it is supposed to be obtained in the following way:--Through
the quicker motion of the point _c'_ the ice between it and _n_ becomes
distended; that is to say, the line _c' n_ is in a state of
strain--there is a _drag_, it is said, oblique to the sides of the
glacier; and it is therefore in this direction that the particles will
be caused to slide past each other. Dr. Whewell, who advocates this
view, thus expounds it. He supposes the case of an alpine valley filled
with india-rubber which has been warmed until it has partially melted,
or become viscous, and then asks, "What will now be the condition of the
mass? The sides and bottom will still be held back by the friction; the
middle and upper part will slide forwards, but not freely. This want of
freedom in the motion (arising from the viscosity) will produce a drag
towards the middle of the valley, where the motion is freest; hence the
direction in which the filaments slide past each other will be obliquely
directed towards the middle. The sliding will separate the mass
according to such lines; and though new attachments will take place, the
mass may be expected to retain the results of this separation in the
traces of parallel fissures."[A] Nothing can be clearer than the image
of the process thus placed before the mind's eye.
One fact of especial importance is to be borne in mind: the sliding of
filaments which is thus supposed to take place oblique to the glacier
has never been proved; it is wholly assumed. A moraine, it is admitted,
will run parallel to the side of a glacier, or a block will move in the
same direction from beginning to end, without being sensibly drawn
towards the centre, but still it is supposed that the sliding of parts
exists, though of a character so small as to render it insensible to
measurement.
[Sidenote: STRUCTURE CROSSES LINES OF SLIDING.]
My chief difficulty as regards this theory may be expressed in a very
few words. If the structure be produced by differential motion, why is
the large and _real_ differential motion which experiments have
established incompetent to produce it? And how can the veins run, as
they are admitted to do, _across the lines of maximum sliding_ from
their origin throughout the glacier to its end?
That a drag towards the centre of the glacier exists is undeniable, but
that in consequence of the drag there is a sliding of filaments in this
direction, is quite another thing. I have in another place[B]
endeavoured to show experimentally that no such sliding takes place,
that the drag on any point towards the centre expresses only half the
conditions of the problem; being exactly neutralized by the thrust
towards the sides. It has been, moreover, shown by Mr. Hopkins that the
lines of maximum strain and of maximum sliding cannot coincide; indeed,
if all the particles be urged by the same force, no matter how strong
the pull may be, there will be no tendency of one to slide past the
other.
FOOTNOTES:
[A] 'Philosophical Magazine,' Ser. III., vol. xxvi.
[B] 'Proceedings of the Royal Institution,' vol. ii. p. 324.
THE RIPPLE-THEORY OF THE VEINED STRUCTURE.
(29.)
[Sidenote: THEORY STATED.]
[Sidenote: THEORY EXAMINED.]
The assumption of oblique sliding, and the production thereby of the
marginal structure, have, however, been fortified by considerations of
an ingenious and very interesting kind. "How," I have asked, "can the
oblique structure persist across the lines of greatest differential
motion throughout the length of the glacier?" But here I am met by
another question which at first sight might seem equally
unanswerable--"How do ripple-marks on the surface of a flowing river,
which are nothing else than lines of differential motion of a low order,
cross the river from the sides obliquely, while the direction of
greatest differential motion is parallel to the sides?" If I understand
aright, this is the main argument of Professor Forbes in favour of his
theory of the oblique marginal structure. It is first introduced in a
note at page 378 of his 'Travels;' he alludes to it in a letter written
the following year; in his paper in the 'Philosophical Transactions' he
develops the theory. He there gives drawings of ripple-marks observed in
smooth gutters after rain, and which he finds to be inclined to the
course of the stream, exactly as the marginal structure is inclined to
the side of the glacier. The explanation also embraces the case of an
obstacle placed in the centre of a river. "A case," writes Professor
Forbes, "parallel to the last mentioned, where a fixed obstacle cleaves
a descending stream, and leaves its trace in a fan-shaped tail, is well
known in several glaciers, as in that at Ferpêcle, and the Glacier de
Lys on the south side of Monte Rosa; particularly the last, where the
veined structure follows the law just mentioned." In his Twelfth Letter
he also refers to the ripples "as exactly corresponding to the position
of the icy bands." In his letter to Dr. Whewell, published in the
'Occasional Papers,' page 58, he writes as follows:--"The same is
remarkably shown in the case of a stream of water, for instance a
mill-race. Although the movement of the water, as shown by floating
bodies, is exceedingly nearly (for small velocities sensibly) parallel
to the sides, yet the variation of the speed from the side to the centre
of the stream occasions a _ripple_, or molecular discontinuity, which
inclines forwards from the sides to the centre of the stream at an angle
with the axis depending on the ratio of the central and lateral
velocity. The veined structure of the ice corresponds to the ripple of
the water, a molecular discontinuity whose measure is not comparable to
the actual velocity of the ice; and therefore the general movement of
the glacier, as indicated by the moraines, remains sensibly parallel to
the sides." This theory opens up to us a series of interesting and novel
considerations which I think will repay the reader's attention. If the
ripples in the water and the veins in the ice be due to the same
mechanical cause, when we develop clearly the origin of the former we
are led directly to the explanation of the latter. I shall now endeavour
to reduce the ripples to their mechanical elements.
The Messrs. Weber have described in their 'Wellenlehre' an effect of
wave-motion which it is very easy to obtain. When a boat moves through
perfectly smooth water, and the rower raises his oar out of the water,
drops trickle from its blade, and each drop where it falls produces a
system of concentric rings. The circular waves as they widen become
depressed, and, if the drops succeed each other with sufficient speed,
the rings cross each other at innumerable points. The effect of this is
to blot out more or less completely all the circles, and to leave
behind two straight divergent ripple-lines, which are tangents to all
the external rings; being in fact formed by the intersections of the
latter, as a caustic in optics is formed by the intersection of luminous
rays. Fig. 48, which is virtually copied from M. Weber, will render this
description at once intelligible. The boat is supposed to move in the
direction of the arrow, and as it does so the rings which it leaves
behind widen, and produce the divergence of the two straight resultant
lines of ripple.
[Sidenote: RIPPLES DEDUCED FROM RINGS.]
[Illustration: Fig. 48. Diagram explanatory of the formation of
Ripples.]
The more quickly the drops succeed each other, the more frequent will be
the intersections of the rings; but as the speed of succession augments
we approach the case of _a continuous vein_ of liquid; and if we suppose
the continuity to be perfectly established, the ripples will still be
produced with a smooth space between them as before. This experiment may
indeed be made with a well-wetted oar, which on its first emergence from
the water sends into it a continuous liquid vein. The same effect is
produced when we substitute for the stream of liquid a solid rod--a
common walking-stick for example. A water-fowl swimming in calm water
produces two divergent lines of ripples of a similar kind.
We have here supposed the water of the lake to be at rest, and the
liquid vein or the solid rod to move through it; but precisely the same
effect is produced if we suppose the rod at rest and the liquid in
motion. Let a post, for example, be fixed in the middle of a flowing
river; diverging from that post right and left we shall have lines of
ripples exactly as if the liquid were at rest and the post moved through
it with the velocity of the river. If the same post be placed close to
the bank, so that _one_ of its edges only shall act upon the water,
diverging from that edge we shall have a _single_ line of ripples which
will cross the river obliquely towards its centre. It is manifest that
any other obstacle will produce the same effect as our hypothetical
post. In the words of Professor Forbes, "the slightest prominence of any
kind in the wall of such a conduit, a bit of wood or a tuft of grass, is
sufficient to produce a well-marked ripple-streak from the side towards
the centre."
[Sidenote: MEASURE OF DIVERGENCE OF RIPPLES.]
The foregoing considerations show that the divergence of the two lines
of ripples from the central post, and of the single line in the case of
the lateral post, have their mechanical element, if I may use the term,
in the experiment of the Messrs. Weber. In the case of a swimming duck
the connexion between the diverging lines of ripples and the propagation
of rings round a disturbed point is often very prettily shown. When the
creature swims with vigour the little foot with which it strikes the
water often comes sufficiently near to the surface to produce an
elevation,--sometimes indeed emerging from the water altogether. Round
the point thus disturbed rings are immediately propagated, and the
widening of those rings is _the exact measure of the divergence of the
ripple lines_. The rings never cross the lines;--the lines never retreat
from the rings.
[Sidenote: RIPPLES AND VEINS DUE TO DIFFERENT CAUSES.]
If we compare the mechanical actions here traced out with those which
take place upon a glacier, I think it will be seen that the analogy
between the ripples and the veined structure is entirely superficial.
How the structure ascribed to the Glacier de Lys is to be explained I do
not know, for I have never seen it; but it seems impossible that it
could be produced, as ripples are, by a fixed obstacle which "cleaves a
descending stream." No one surely will affirm that glacier-ice so
closely resembles a fluid as to be capable of transmitting undulations,
as water propagates rings round a disturbed point. The difficulty of
such a supposition would be augmented by taking into account the motion
of the _individual liquid particles_ which go to form a ripple; for the
Messrs. Weber have shown that these move in closed curves, describing
orbits more or less circular. Can it be supposed that the particles of
ice execute a motion of this kind? If so, their orbital motions may be
easily calculated, being deducible from the motion of the glacier
compounded with the inclination of the veins. If so important a result
could be established, all glacier theories would vanish in comparison
with it.
[Sidenote: POSITION OF RIPPLES NOT THAT OF STRUCTURE.]
There is another interesting point involved in the passage above quoted.
Professor Forbes considers that the ripple is occasioned by the
variation of speed from the side to the centre of the stream, and that
its _inclination_ depends on the ratio of the central and lateral
velocity. If I am correct in the above analysis, this cannot be the
case. The inclination of the ripple depends solely on the ratio of the
river's translatory motion to the velocity of its wave-motion. Were the
lateral and central velocities alike, a momentary disturbance at the
side would produce a _straight_ ripple-mark, whose inclination would be
compounded of the two elements just mentioned. If the motion of the
water vary from side to centre, the velocity of wave-propagation
remaining constant, the inclination of the ripple will also vary, that
is to say, we shall have a _curved_ ripple instead of a straight one.
This, of course, is the case which we find in Nature, but the curvature
of such ripples is totally different from that of the veined structure.
Owing to the quicker translatory movement, the ripples, as they approach
the centre, tend more to parallelism with the direction of the river;
and after having passed the centre, and reached the slower water near
the opposite side, their inclination to the axis gradually augments.
Thus the ripples from the two sides form a pair of symmetric curves,
which cross each other at the centre, and possess the form _a o b_, _c o
d_, shown in Fig. 49. A similar pair of curves would be produced by the
reflection of these. Knowing the variation of motion from side to
centre, any competent mathematician could find the equation of the
ripple-curves; but it would be out of place for me to attempt it here.
[Illustration: Fig. 49. Diagram explanatory of the formation of
Ripples.]
THE VEINED STRUCTURE AND PRESSURE.
(30.)
If a prism of glass be pressed by a sufficient weight, the particles in
the line of pressure will be squeezed more closely together, while those
at right angles to this line will be forced further apart. The existence
of this state of strain may be demonstrated by the action of such
squeezed glass upon polarised light. It gives rise to colours, and it is
even possible to infer from the tint the precise amount of pressure to
which the glass is subjected. M. Wertheim indeed has most ably applied
these facts to the construction of a dynamometer, or instrument for
measuring pressures, exceeding in accuracy any hitherto devised.
When the pressure applied becomes too great for the glass to sustain, it
flies to pieces. But let us suppose the sides of the prism defended by
an extremely strong jacket, in which the prism rests like a
closely-fitting plug, and which yields only when a pressure more than
sufficient to crush the glass is applied. Let the pressure be gradually
augmented until this point is attained; afterwards both the glass and
its jacket will shorten and widen; the jacket will yield laterally,
being pushed out with extreme slowness by the glass within.
[Sidenote: POSSIBLE EXPERIMENT WITH GLASS PRISM.]
Now I believe that it would be possible to make this experiment in such
a manner that the glass should be _flattened_, partly through rupture,
and partly through lateral molecular yielding; the prism would change
its form, and yet present a firmly coherent mass when removed from its
jacket. I have never made the experiment; nobody has, as far as I know;
but experiments of this kind are often made by Nature. In the Museum of
the Government School of Mines, for example, we have a collection of
quartz stones placed there by Mr. Salter, and which have been subjected
to enormous pressure in the neighbourhood of a fault. These rigid
pebbles have, in some cases, been squeezed against each other so as to
produce mutual flattening and indentation. Some of them have yielded
along planes passing through them, as if one half had slidden over the
other; but the reattachment is very strong. Some of the larger stones,
moreover, which have endured pressure at a particular point, are
fissured radially around this point. In short, the whole collection is a
most instructive example of the manner and extent to which one of the
most rigid substances in Nature can yield on the application of a
sufficient force.
[Sidenote: POSSIBLE EXPERIMENT WITH PRISM OF ICE.]
Let a prism of ice at 32° be placed in a similar jacket to that which we
have supposed to envelop the glass prism. The ice yields to the pressure
with incomparably greater ease than the glass; and if the force be
slowly applied, the lateral yielding will far more closely resemble that
of a truly plastic body. Supposing such a piece of ice to be filled with
numerous small air-bubbles, the tendency of the pressure would be to
flatten these bubbles, and to squeeze them out of the ice. Were the
substance perfectly homogeneous, this flattening and expulsion would
take place uniformly throughout its entire mass; but I believe there is
no such homogeneous substance in nature;--the ice will yield at
different places, leaving between them spaces which are comparatively
unaffected by the pressure. From the former spaces the air-bubbles will
be more effectually expelled; and I have no doubt that the result of
such pressure acting upon ice so protected would be to produce a
laminated structure somewhat similar to that which it produces in those
bodies which exhibit slaty cleavage.
[Sidenote: LAMINATION PRODUCED BY PRESSURE.]
[Sidenote: NO SLIDING OF FILAMENTS.]
I also think it certain that, in this lateral displacement of the
particles, these must move past each other. This is an idea which I
have long entertained, as the following passage taken from the paper
published by Mr. Huxley and myself will prove:--"Three principal causes
may operate in producing cleavage: first, the reducing of surfaces of
weak cohesion to parallel planes; second, the flattening of minute
cavities; and third, the weakening of cohesion by tangential action. The
third action is exemplified by the state of the rails near a station
where a break is habitually applied to a locomotive. In this case, while
the weight of the train presses vertically, its motion tends to cause
longitudinal sliding of the particles of the rail. Tangential action
does not, however, necessarily imply a force of the latter kind. When a
solid cylinder an inch in height is squeezed to a vertical cake a
quarter of an inch in height, it is impossible, physically speaking,
that the particles situated in the same vertical line shall move
laterally with the same velocity; but if they do not, the cohesion
between them will be weakened or ruptured. The pressure, however, will
produce new contact; and if this have a cohesive value equal to that of
the old contact, no cleavage from this cause can arise. The relative
capacities of different substances for cleavage appear to depend in a
great measure upon their different properties in this respect. In
butter, for example, the new attachments are equal, or nearly so, to the
old, and the cleavage is consequently indistinct; in wax this does not
appear to be the case, and hence may arise in a great degree the
perfection of its cleavage. The further examination of this subject
promises interesting results." I would dwell upon this point the more
distinctly as the advocates of differential motion may deem it to be in
their favour; but it appears to me that the mechanical conceptions
implied in the above passage are totally different from theirs. If they
think otherwise, then it seems to me that they should change the
expressions which refer the differential motion to a "drag" towards the
centre, and the structure to the sliding of "filaments" past each other
in consequence of this drag. Such filamentary sliding may take place in
a truly viscous body, but it does not take place in ice.
In one particular the ice resembles the butter referred to in the above
quotation; for its new attachments appear to be equal to the old, and
this, I think, is to be ascribed to its perfect regelation. As justly
pointed out by Mr. John Ball, the veined ice of a glacier, if
unweathered, shows no tendency to cleave; for though the expulsion of
the air-bubbles has taken place, the reattachment of the particles is so
firm as to abolish all evidence of cleavage. When the ice, on the
contrary, is weathered, the plates become detached, and I have often
been able to split such ice into thin tablets having an area of two or
three square feet.
In his Thirteenth Letter Professor Forbes throws out a new and possibly
a pregnant thought in connexion with the veins. If I understand him
aright--and I confess it is usually a matter of extreme difficulty with
me to make sure of this--he there refers the veins, not to the expulsion
of the air from the ice, but to its redistribution. The pressure
produces "_lines of tearing_ in which the air is distributed in the form
of regular globules." I do not know what might be made of this idea if
it were developed, but at present I do not see how the supposed action
could produce the blue bands; and I agree with Professor Wm. Thomson in
regarding the explanation as improbable.[A]
FOOTNOTES:
[A] For an extremely ingenious view of the origin of the veined
structure, I would refer to a paper by Professor Thomson, in the
'Proceedings of the Royal Society,' April, 1858.
THE VEINED STRUCTURE AND THE LIQUEFACTION OF ICE BY PRESSURE.
(31.)
I have already noticed an important fact for which we are indebted to
Mr. James Thomson, and have referred to the original communications on
the subject. I shall here place the physical circumstances connected
with this fact before my reader in the manner which I deem most likely
to interest him.
[Sidenote: INFLUENCE OF PRESSURE ON BOILING POINT.]
When a liquid is heated, the attraction of the molecules operates
against the action of the heat, which tends to tear them asunder. At a
certain point the force of heat triumphs, the cohesion is overcome, and
the liquid boils. But supposing we assist the attraction of the
molecules by applying an external pressure, the difficulty of tearing
them asunder will be increased; more heat will be required for this
purpose; and hence we say that the _boiling point_ of the liquid has
been _elevated_ by the pressure.
[Sidenote: INFLUENCE OF PRESSURE ON FUSING POINT.]
If molten sulphur be poured into a bullet-mould, it will be found on
cooling to contract, so as to leave a large hollow space in the middle
of each sphere. Cast musket-bullets are thus always found to possess a
small cavity within them produced by the contraction of the lead.
Conceive the bullet placed within its mould and the latter heated; to
produce fusion it is necessary that the sulphur or the lead should
_swell_. Here, as in the case of the heated water, the tendency to
expand is opposed by the attraction of the molecules; with a certain
amount of heat however this attraction is overcome and the solid
_melts_. But suppose we assist the molecular attraction by a suitable
force applied externally, a greater amount of heat than before will be
necessary to tear them asunder; and hence we say that the _fusing
point_ has been _elevated_ by the pressure. This fact has been
experimentally established by Messrs. Hopkins and Fairbairn, who applied
to spermaceti and other substances pressures so great as to raise their
points of fusion a considerable number of degrees.
Let us now consider the case of the metal bismuth. If the molten metal
be poured into a bullet-mould it will _expand_ on solidifying. I have
myself filled a strong cast-iron bottle with the metal, and found its
expansion on cooling sufficiently great to split the bottle from neck to
bottom. Hence, in order to fuse the bismuth the substance must
_contract_; and it is manifest that an external pressure which tends to
squeeze the molecules more closely together here _assists_ the heat
instead of opposing it. Hence, to fuse bismuth under great pressure, a
less amount of heat will be required than when the pressure is removed;
or, in other words, the fusing point of bismuth is _lowered_ by the
pressure. Now, in passing from the solid to the liquid state, _ice_,
like bismuth, contracts, and if the contraction be promoted by external
pressure, as shown by the Messrs. Thomson, a less amount of heat
suffices to liquefy it.
[Sidenote: EXPERIMENTS.]
These remarks will enable us to understand a singular effect first
obtained by myself at the close of 1856 or in January 1857, noticed at
the time in the 'Proceedings of the Royal Society,' and afterwards fully
described in a paper presented to the Society in December of that year.
A cylinder of clear ice two inches high and an inch in diameter was
placed between two slabs of box-wood, and subjected to a gradual
pressure. I watched the ice in a direction perpendicular to its length,
and saw cloudy lines drawing themselves across it. As the pressure
continued, these lines augmented in numbers, until finally the prism
presented the appearance of a crystal of gypsum whose planes of cleavage
had been forced out of optical contact. When looked at obliquely it was
found that the lines were merely the sections of flat dim surfaces,
which lay like laminæ one over the other throughout the length of the
prism. Fig. 50 represents the prism as it appeared when looked at in a
direction perpendicular to its axis; Fig. 51 shows the appearance when
viewed obliquely.[A]
[Illustration: Fig. 50, 51. Appearance of a prism of ice partially
liquefied by Pressure.]
At first sight it might appear as if air had intruded itself between the
separated surfaces of the ice, and to test this point I placed a
cylinder two inches long and an inch wide upright in a copper vessel
which was filled with ice-cold water. The ice cylinder rose about half
an inch above the surface of the water. Placing the copper vessel on a
slab of wood, and a second slab on the top of the cylinder of ice, the
latter was subjected to the gradual action of a small hydraulic press.
When the hazy surfaces were well developed in the portion of the ice
above the water, the cylinder was removed and examined: the planes of
rupture extended throughout the entire length of the cylinder, just as
if it had been squeezed in air. I subsequently placed the ice in a stout
vessel of glass, and squeezed it, as in the last experiment: the
surfaces of discontinuity were seen forming _under the liquid_ quite as
distinctly as in air.
To prove that the surfaces were due to compression and not to any
tearing asunder of the mass by tension, the following experiment was
made:--A cylindrical piece of ice, one of whose ends, however, was not
parallel to the other, was placed between the slabs of wood, and
subjected to pressure. Fig. 52 shows the disposition of the experiment.
The effect upon the ice cylinder was that shown in Fig. 53, the surfaces
being developed along that side which had suffered the pressure. On
examining the surfaces by a pocket lens they resembled the effect
produced upon a smooth cold surface by breathing on it.
[Illustration: Fig. 52, 53. Figures illustrative of compression and
liquefaction of ice.]
[Sidenote: LIQUID LAYERS PRODUCED BY PRESSURE.]
The surfaces were always dim; and had the spaces been filled with air,
or were they simply vacuous, the reflection of light from them would
have been so copious as to render them much more brilliant than they
were observed to be. To examine them more particularly I placed a
concave mirror so as to throw the diffused daylight from a window full
upon the cylinder. On applying the pressure dim spots were sometimes
seen forming in the very middle of the ice, and these as they expanded
laterally appeared to be in a state of intense motion, which followed
closely the edge of each surface as it advanced through the solid ice.
Once or twice I observed the hazy surfaces pioneered through the mass by
dim offshoots, apparently liquid, and constituting a kind of
decrystallisation. From the closest examination to which I was able to
subject them, the surfaces appeared to me to be due to internal
liquefaction; indeed, when the melting point of ice, having already a
temperature of 32°, is lowered by pressure, its excess of heat must
instantly be applied to produce this effect.
[Sidenote: APPLICATION TO THE VEINED STRUCTURE.]
I have already given a drawing (p. 386) showing the development of the
veined structure at the base of the ice-cascade of the Rhone; and if we
compare that diagram with Fig. 53 a striking similarity at once reveals
itself. The ice of the glacier must undoubtedly be liquefied to some
extent by the tremendous pressure to which it is here subjected.
Surfaces of discontinuity will in all probability be formed, which
facilitate the escape of the imprisoned air. The small quantity of water
produced will be partly imbibed by the adjacent porous ice, and will be
refrozen when relieved from the pressure. This action, associated with
that ascribed to pressure in the last section, appears to me to furnish
a complete physical explanation of the laminated structure of
glacier-ice.
FOOTNOTES:
[A] This effect projected upon a screen is a most striking and
instructive class experiment.
WHITE ICE-SEAMS IN THE GLACIER DU GÉANT.
(32.)
[Sidenote: GENERAL APPEARANCE OF WHITE ICE-SEAMS.]
On the 28th of July, 1857, while engaged upon the Glacier du Géant, my
attention was often attracted by protuberant ridges of what at first
appeared to be pure white snow, but which on examination I found to be
compact ice filled with innumerable round air-cells; and which, in
virtue of its greater power of resistance to wasting, often rose to a
height of three or four feet above the general level of the ice. As I
stood amongst these ridges, they appeared detached and without order of
arrangement, but looked at from a distance they were seen to sweep
across the proper Glacier du Géant in a direction concentric with its
dirt-bands and its veined structure. In some cases the seams were
admirable indications of the relative displacement of two adjacent
portions of the glacier, which were divided from each other by a
crevasse. Usually the sections of a seam exposed on the opposite sides
of a fissure accurately faced each other, and the direction of the seam
on both sides was continuous; but at other places they demonstrated the
existence of lateral faults, being shifted asunder laterally through
spaces varying from a few inches to six or seven feet.
On the following day I was again upon the same glacier, and noticed in
many cases the white ice-seams exquisitely honeycombed. The case was
illustrative of the great difference between the absorptive power of the
ice itself and of the objects which lie upon its surface. Deep
cylindrical cells were produced by spots of black dirt which had been
scattered upon the surface of the white ice, and which sank to a depth
of several inches into the mass. I examined several sections of the
veins, and in general I found that their deeper portions blended
gradually with the ice on either side of them. But higher up the glacier
I found that the veins penetrated only to a limited depth, and did not
therefore form an integrant portion of the glacier. Figs. 54 and 55 show
the sections of two of the seams which were exposed on the wall of a
crevasse at some distance below the great ice-fall of the Glacier du
Géant.
[Sidenote: SECTIONS OF SEAMS.]
[Illustration: Fig. 54, 55. Sections of White Ice-seams.]
[Illustration: Fig. 56. Variations in the Dip of the Veined Structure.]
It was at the base of the Talèfre cascade that the explanation of these
curious seams presented itself to me. In one of my earliest visits to
this portion of the glacier I was struck by a singular disposition of
the blue veins on the vertical wall of a crevasse. Fig. 56 will
illustrate what I saw. The veins, within a short distance, dipped
_backward_ and _forward_, like the junctions of stones used to turn an
arch. In some cases I found this variation of the structure so great as
to pass in a short distance from the vertical to the horizontal, as
shown in Fig. 57.
[Sidenote: VARIATIONS IN "DIP" OF STRUCTURE.]
[Illustration: Fig. 57. Variations in the Dip of the Veined Structure.]
Further examination taught me that the glacier here is crumpled in a
most singular manner; doubtless by the great pressure to which it is
exposed. The following illustration will convey a notion of its aspect:
Let one hand be laid flat upon a table, palm downwards, and let the
fingers be bent until the space between the first joint and the ends of
the fingers is vertical; one of the crumples to which I refer will then
be represented. The ice seems bent like the fingers, and the crumples of
the glacier are cut by crevasses, which are accurately typified by the
spaces between the fingers. Let the second hand now be placed upon the
first, as the latter is upon the table, so that the tops of the bent
fingers of the second hand shall rest upon the roots of the first: two
crumples would thus be formed; a series of such protuberances, with
steep fronts, follow each other from the base of the Talèfre cascade for
some distance downwards.
On Saturday the 1st of August I ascended these rounded terraces in
succession, and observed among them an extremely remarkable disposition
of the structure. Fig. 58 is a section of a series of three of the
crumples, on which the shading lines represent the direction of the blue
veins. At the base of each protuberance I found a seam of white ice
wedged firmly into the glacier, and _each of the seams marked a place of
dislocation of the veins_. The white seams thinned off gradually, and
finally vanished where the violent crumpling of the ice disappeared. In
Fig. 59 I have sketched the wall of a crevasse, which represents what
may be regarded as the incipient crumpling. The undulating line shows
the contour of the surface, and the shading lines the veins. It will be
observed that the direction of the veins yields in conformity with the
undulation of the surface; and an augmentation of the effect would
evidently result in the crumples shown in Fig. 58. The appearance of the
white seams at those places where a dislocation occurred was, as far as
I could observe, invariable; but in a few instances the seams were
observed upon the platforms of the terraces, and also upon their slopes.
The width of a seam was very irregular, varying from a few inches at
some places to three or four feet at others.
[Sidenote: CRUMPLES OF THE TALÈFRE.]
[Illustration: Fig. 58. Section of three glacier Crumples.]
[Illustration: Fig. 59. Wall of a crevasse, with incipient crumpling.]
[Sidenote: MOULDS OF WHITE ICE-SEAMS.]
On the 3rd of August I was again at the base of the Talèfre cascade, and
observed a fact the significance of which had previously escaped me. The
rills which ran down the ice-slopes collected at the base of each
protuberance into a stream, which, at the time of my visit, had hollowed
out for itself a deep channel in the ice. At some places the stream
widened, at others its banks of ice approached each other, and rapids
were produced; in fact, _the channels of such streams appeared to be the
exact moulds of the seams of white ice_.
Instructed thus far, I ascended the Glacier du Géant on the 5th of
August, and then observed on the wrinkles of this glacier the same
leaning backwards and forwards of the blue veins as I had previously
observed upon the Talèfre. I also noticed on this day that a seam of
white ice would sometimes open out into two branches, which, after
remaining for some distance separate, would reunite and thus enclose a
little glacier-island. At other places lateral branches were thrown off
from the principal seam, thus suggesting the form of a glacier-rivulet
which had been fed by tributary branches. On the 7th of August I hunted
the seams still farther up the glacier; and found them at one place
descending a steep ice-hill, being crossed by other similar bands, which
however were far less white and compact. I followed these new bands to
their origin, and found it to be a system of crevasses formed at the
summit of the hill, some of which were filled with snow. Lower down the
crevasses closed, and the snow thus jammed between their walls was
converted into white ice. These seams, however, never attained the
compactness and prominence of the larger ones which had their origin far
higher up. I singled out one of the best of the latter, and traced it
through all the dislocation and confusion of the ice, until I found it
to terminate in a cavity filled with snow.
This was near the base of the _séracs_, and the streams here were
abundant. Comparing the shapes of some of them with that of the
ice-bands lower down the glacier, a striking resemblance was observed.
Fig. 60 is the plan of a deep-cut channel through which a stream flowed
on the day to which I now refer. Fig. 61 is the plan of a seam of white
ice sketched on the same day, low down upon the glacier. Instances of
this kind might be multiplied; and the result, I think, renders it
certain that the white ice-seams referred to are due to the filling up
of the channels of glacier-streams by snow during winter, and the
subsequent compression of the mass to ice during the descent of the
glacier. I have found such seams at the bases of all cascades that I
have visited; and in all cases they appear to be due to the same cause.
The depth to which they penetrate the glacier must be profound, or the
_ablation_ of the ice must be less than what is generally supposed; for
the seams formed so high up on the Glacier du Géant may be traced low
down upon the trunk-stream of the Mer de Glace.[A]
[Sidenote: STREAMS AND SEAMS.]
[Illustration: Fig. 60. Plan of a Stream on the Glacier du Géant.]
[Illustration: Fig. 61. Plan of a Seam of White Ice on the Glacier du
Géant.]
[Sidenote: SCALING OFF BY PRESSURE.]
These observations on the white ice-seams enable us to add an important
supplement to what has been stated regarding the origin of the
dirt-bands of the Mer de Glace; The protuberances at the base of the
cascade are due not only to the toning down of the ridges produced by
the transverse fracture of the glacier at the summit of the fall, but
they undergo modifications by the pressure locally exerted at its base.
The state of things represented in Fig. 57 is plainly due to the partial
pushing of one crumple over that next in advance of it. There seems to
be a differential motion of the parts of the glacier in the same
longitudinal line; showing that upon the general motion of the glacier
smaller local motions are superposed. The occurrence of the seams upon
the faces of the slopes seems also to prove that the pressure is
competent, in some cases, to cause the bases of the protuberances to
swell, so that what was once the base of a crumple may subsequently form
a portion of its slope. Another interesting fact is also observed where
the pressure is violent: the crumples _scale off_, bows of ice being
thus formed which usually span the crumples over their most violently
compressed portions. I have found this scaling off at the bases of all
the cascades which I have visited, and it is plainly due to the pressure
exerted at such places upon the ice.
FOOTNOTES:
[A] The more permanent seams may possibly be due to the filling of the
profound crevasses of the cascade.
(33.)
[Sidenote: COMPRESSION OF GLACIER DU GÉANT.]
Not only at the base of its great cascade, but throughout the greater
part of its length, the Glacier du Géant is in a state of longitudinal
compression. The meaning of this term will be readily understood: Let
two points, for example, be marked upon the axis of the glacier; if
these during its descent were drawn wider apart, it would show that the
glacier was in a state of longitudinal strain or tension; if they
remained at the same distance apart, it would indicate that neither
strain nor pressure was exerted; whereas, if the two points approached
each other, which could only be by the quicker motion of the hinder
one, the existence of longitudinal compression would be thereby
demonstrated.
Taking "Le Petit Balmat" with me, to carry my theodolite, I ascended the
Glacier du Géant until I came near the place where it is joined by the
Glacier des Périades, and whence I observed a patch of fresh green grass
upon the otherwise rocky mountain-side. To this point I climbed, and
made it the station for my instrument. Choosing a well-defined object at
the opposite side of the glacier, I set, on the 9th of August, in the
line between this object and the theodolite, three stakes, one in the
centre of the glacier, and the other two at opposite sides of the centre
and about 100 yards from it. This done, I descended for a quarter of a
mile, when I again climbed the flanking rocks, placing my theodolite in
a couloir, down which stones are frequently discharged from the end of a
secondary glacier which hangs upon the heights above. Here, as before, I
fixed three stakes, chiselled a mark upon the granite, so as to enable
me to find the place, and regained the ice without accident. A day or
two previously we had set out a third line at some distance lower down,
and I was thus furnished with a succession of points along the glacier,
the relative motions of which would decide whether it was _pressed_ or
_stretched_ in the direction of its length. On the 10th of August Mr.
Huxley joined us; and on the following day we all set out for the
Glacier du Géant, to measure the progress of the stakes which I had
fixed there. Hirst remained upon the glacier to measure the
displacements; I shouldered the theodolite; and Huxley was my guide to
the mountain-side, sounding in advance of me the treacherous-looking
snow over which we had to pass.
Calling the central stake of the highest line No. 1, that of the middle
line No. 2, and that of the line nearest the Tacul No. 3, the following
are the spaces moved over by these three points in twenty-four hours:
Inches. Distances asunder.
No. 1 20.55
} 545 yards.
No. 2 15.43
} 487 yards.
No. 3 12.75
Here we have the fact which the aspect of the glacier suggested. The
first stake moves five inches a day more than the second, and the second
nearly three inches a day more than the third. As surmised, therefore,
the glacier is in a state of longitudinal compression, whereby a portion
of it 1000 yards in length is shortened at the rate of eight inches a
day.
[Sidenote: STRUCTURE IN WHITE ICE-SEAMS.]
In accordance with this result, the transverse undulations of the
Glacier du Géant, described in the chapter upon Dirt-Bands, _shorten_ as
they descend. A series of three of them measured along the axis of the
glacier on the 6th of August, 1857, gave the following respective
lengths:--955 links, 855 links, 770 links, the shortest undulation being
the farthest from the origin of the undulations. This glacier then
constitutes a vast ice-press, and enables us to test the explanation
which refers the veined structure of the ice to pressure. The glacier
itself is transversely laminated, as already stated; and in many cases a
structure of extreme definition and beauty is developed in the
compressed snow, which constitutes the seams of white ice. In 1857 I
discovered a well-developed lenticular structure in some of these seams.
In 1858 I again examined them. Clearing away the superficial portions
with my axe, I found, drawn through the body of the seams, long lines of
blue ice of exquisite definition; in fact, I had never seen the
structure so delicately exhibited. The seams, moreover, were developed
in portions of the white ice which were near the _centre_ of the
glacier, and where consequently filamentous sliding was entirely out of
the question.
[Sidenote: PARTIAL SUMMARY.]
PARTIAL SUMMARY.
1. Glaciers are derived from mountain snow, which has been consolidated
to ice by pressure.
2. That pressure is competent to convert snow into ice has been proved
by experiment.
3. The power of yielding to pressure diminishes as the mass becomes more
compact; but it does not cease even when the substance has attained the
compactness which would entitle it to be called ice.
4. When a sufficient depth of snow collects upon the earth's surface,
the lower portions are squeezed out by the pressure of the
superincumbent mass. If it rests upon a slope it will yield principally
in the direction of the slope, and move downwards.
5. In addition to this, the whole mass slides bodily along its inclined
bed, and leaves the traces of its sliding on the rocks over which it
passes, grinding off their asperities, and marking them with grooves and
scratches in the direction of the motion.
6. In this way the deposit of consolidated and unconsolidated snow which
covers the higher portions of lofty mountains moves slowly down into an
adjacent valley, through which it descends as a true glacier, partly by
sliding and partly by the yielding of the mass itself.
7. Several valleys thus filled may unite in a single valley, the
tributary glaciers welding themselves together to form a trunk-glacier.
8. Both the main valley and its tributaries are often sinuous, and the
tributaries must change their direction to form the trunk; the width of
the valley often varies. The glacier is forced through narrow gorges,
widening after it has passed them; the centre of the glacier moves more
quickly than the sides, and the surface more quickly than the bottom;
the point of swiftest motion follows the same law as that observed in
the flow of rivers, shifting from one side of the centre to the other as
the flexure of the valley changes.
9. These various effects may be reproduced by experiments on small
masses of ice. The substance may moreover be moulded into vases and
statuettes. Straight bars of it may be bent into rings, or even coiled
into knots.
10. Ice, capable of being thus moulded, is practically incapable of
being stretched. The condition essential to success is that the
particles of the ice operated on shall be kept in close contact, so that
when old attachments have been severed new ones may be established.
11. The nearer the ice is to its melting point in temperature, the more
easily are the above results obtained; when ice is many degrees below
its freezing point it is crushed by pressure to a white powder, and is
not capable of being moulded as above.
12. Two pieces of ice at 32° Fahr., with moist surfaces, when placed in
contact freeze together to a rigid mass; this is called Regelation.
13. When the attachments of pressed ice are broken, the continuity of
the mass is restored by the regelation of the new contiguous surfaces.
Regelation also enables two tributary glaciers to weld themselves to
form a continuous trunk; thus also the crevasses are mended, and the
dislocations of the glacier consequent on descending cascades are
repaired. This healing of ruptures extends to the smallest particles of
the mass, and it enables us to account for the continued compactness of
the ice during the descent of the glacier.
14. The quality of viscosity is practically absent in glacier-ice. Where
pressure comes into play the phenomena are suggestive of viscosity, but
where tension comes into play the analogy with a viscous body breaks
down. When subjected to strain the glacier does not yield by stretching,
but by breaking; this is the origin of the crevasses.
15. The crevasses are produced by the mechanical strains to which the
glacier is subjected. They are divided into marginal, transverse, and
longitudinal crevasses; the first produced by the oblique strain
consequent on the quicker motion of the centre; the second by the
passage of the glacier over the summit of an incline; the third by
pressure from behind and resistance in front, which causes the mass to
split at right angles to the pressure [strain?].
16. The moulins are formed by deep cracks intersecting glacier rivulets.
The water in descending such cracks scoops out for itself a shaft,
sometimes many feet wide, and some hundreds of feet deep, into which the
cataract plunges with a sound like thunder. The supply of water is
periodically cut off from the moulins by fresh cracks, in which new
moulins are formed.
17. The lateral moraines are formed from the débris which loads the
glacier along its edges; the medial moraines are formed on a
trunk-glacier by the union of the lateral moraines of its tributaries;
the terminal moraines are formed from the débris carried by the glacier
to its terminus, and there deposited. The number of medial moraines on a
trunk glacier is always one less than the number of tributaries.
18. When ordinary lake-ice is intersected by a strong sunbeam it
liquefies so as to form flower-shaped figures within the mass; each
flower consists of six petals with a vacuous space at the centre; the
flowers are always formed parallel to the planes of freezing, and depend
on the crystallization of the substance.
19. Innumerable liquid disks, with vacuous spots, are also formed by the
solar beams in glacier-ice. These empty spaces have been hitherto
mistaken for air-bubbles, the flat form of the disks being erroneously
regarded as the result of pressure.
20. These disks are indicators of the intimate constitution of
glacier-ice, and they teach us that it is composed of an aggregate of
parts with surfaces of crystallization in all possible planes.
21. There are also innumerable small cells in glacier-ice holding air
and water; such cells also occur in lake-ice; and here they are due to
the melting of the ice in contact with the bubble of air. Experiments
are needed on glacier-ice in reference to this point.
22. At a free surface within or without, ice melts with more ease than
in the centre of a compact mass. The motion which we call heat is less
controlled at a free surface, and it liberates the molecules from the
solid condition sooner than when the atoms are surrounded on all sides
by other atoms which impede the molecular motion. Regelation is the
complementary effect to the above; for here the superficial portions of
a mass of ice are made virtually central by the contact of a second
mass.
23. The dirt-bands have their origin in the ice-cascades. The glacier,
in passing the brow, is transversely fractured; ridges are formed with
hollows between them; these transverse hollows are the principal
receptacles of the fine débris scattered over the glacier; and after the
ridges have been melted away, the dirt remains in successive stripes
upon the glacier.
24. The ice of many glaciers is laminated, and when weathered may be
cloven into thin plates. In the sound ice the lamination manifests
itself in blue stripes drawn through the general whitish mass of the
glacier; these blue veins representing portions of ice from which the
air-bubbles have been more completely expelled. This is the veined
structure of the ice. It is divided into marginal, transverse, and
longitudinal structure; which may be regarded as complementary to
marginal, longitudinal, and transverse crevasses. The latter are
produced by tension, the former by pressure, which acts in two different
ways: firstly, the pressure acts upon the ice as it has acted upon rocks
which exhibit the lamination technically called cleavage; secondly, it
produces partial liquefaction of the ice. The liquid spaces thus formed
help the escape of the air from the glacier; and the water produced,
being refrozen when the pressure is relieved, helps to form the blue
veins.
APPENDIX.
COMPARATIVE VIEW OF THE CLEAVAGE OF CRYSTALS AND SLATE-ROCKS.
A LECTURE DELIVERED AT THE ROYAL INSTITUTION, ON FRIDAY EVENING THE 6TH
OF JUNE, 1856.[A]
When the student of physical science has to investigate the character of
any natural force, his first care must be to purify it from the mixture
of other forces, and thus study its simple action. If, for example, he
wishes to know how a mass of water would shape itself, supposing it to
be at liberty to follow the bent of its own molecular forces, he must
see that these forces have free and undisturbed exercise. We might
perhaps refer him to the dew-drop for a solution of the question; but
here we have to do, not only with the action of the molecules of the
liquid upon each other, but also with the action of gravity upon the
mass, which pulls the drop downwards and elongates it. If he would
examine the problem in its purity, he must do as Plateau has done,
withdraw the liquid mass from the action of gravity, and he would then
find the shape of the mass to be perfectly spherical. Natural processes
come to us in a mixed manner, and to the uninstructed mind are a mass of
unintelligible confusion. Suppose half-a-dozen of the best musical
performers to be placed in the same room, each playing his own
instrument to perfection: though each individual instrument might be a
well-spring of melody, still the mixture of all would produce mere
noise. Thus it is with the processes of nature. In nature, mechanical
and molecular laws mingle, and create apparent confusion. Their mixture
constitutes what may be called the _noise_ of natural laws, and it is
the vocation of the man of science to resolve this noise into its
components, and thus to detect the "music" in which the foundations of
nature are laid.
The necessity of this detachment of one force from all other forces is
nowhere more strikingly exhibited than in the phenomena of
crystallization. I have here a solution of sulphate of soda. Prolonging
the mental vision beyond the boundaries of sense, we see the atoms of
that liquid, like squadrons under the eye of an experienced general,
arranging themselves into battalions, gathering round a central
standard, and forming themselves into solid masses, which after a time
assume the visible shape of the crystal which I here hold in my hand. I
may, like an ignorant meddler wishing to hasten matters, introduce
confusion into this order. I do so by plunging this glass rod into the
vessel. The consequent action is not the pure expression of the
crystalline forces; the atoms rush together with the confusion of an
unorganized mob, and not with the steady accuracy of a disciplined host.
Here, also, in this mass of bismuth we have an example of this confused
crystallization; but in the crucible behind me a slower process is going
on: here there is an architect at work "who makes no chips, no din," and
who is now building the particles into crystals, similar in shape and
structure to those beautiful masses which we see upon the table. By
permitting alum to crystallize in this slow way, we obtain these perfect
octahedrons; by allowing carbonate of lime to crystallize, nature
produces these beautiful rhomboids; when silica crystallizes, we have
formed these hexagonal prisms capped at the ends by pyramids; by
allowing saltpetre to crystallize, we have these prismatic masses; and
when carbon crystallizes, we have the diamond. If we wish to obtain a
perfect crystal, we must allow the molecular forces free play: if the
crystallizing mass be permitted to rest upon a surface it will be
flattened, and to prevent this a small crystal must be so suspended as
to be surrounded on all sides by the liquid, or, if it rest upon the
surface, it must be turned daily so as to present all its faces in
succession to the working builder. In this way the scientific man nurses
these children of his intellect, watches over them with a care worthy of
imitation, keeps all influences away which might possibly invade the
strict morality of crystalline laws, and finally sees them developed
into forms of symmetry and beauty which richly reward the care bestowed
upon them.
In building up crystals, these little atomic bricks often arrange
themselves into layers which are perfectly parallel to each other, and
which can be separated by mechanical means; this is called the cleavage
of the crystal. I have here a crystallized mass which has thus far
escaped the abrading and disintegrating forces which, sooner or later,
determine the fate of sugar-candy. If I am skilful enough, I shall
discover that this crystal of sugar cleaves with peculiar facility in
one direction. Here, again, I have a mass of rock-salt: I lay my knife
upon it, and with a blow cleave it in this direction; but I find on
further examining this substance that it cleaves in more directions than
one. Laying my knife at right angles to its former position, the crystal
cleaves again; and, finally placing the knife at right angles to the
two former positions, the mass cleaves again. Thus rock-salt cleaves in
three directions, and the resulting solid is this perfect cube, which
may be broken up into any number of smaller cubes. Here is a mass of
Iceland spar, which also cleaves in three directions, not at right
angles, but obliquely to each other, the resulting solid being a
rhomboid. In each of these cases the mass cleaves with equal facility in
all three directions. For the sake of completeness, I may say that many
substances cleave with unequal facility in different directions, and the
heavy spar I hold in my hand presents an example of this kind of
cleavage.
Turn we now to the consideration of some other phenomena to which the
term cleavage may be applied. This piece of beech-wood cleaves with
facility parallel to the fibre, and if our experiments were fine enough
we should discover that the cleavage is most perfect when the edge of
the axe is laid across the rings which mark the growth of the tree. The
fibres of the wood lie side by side, and a comparatively small force is
sufficient to separate them. If you look at this mass of hay severed
from a rick, you will see a sort of cleavage developed in it also; the
stalks lie in parallel planes, and only a small force is required to
separate them laterally. But we cannot regard the cleavage of the tree
as the same in character as the cleavage of the hayrick. In the one case
it is the atoms arranging themselves according to organic laws which
produce a cleavable structure; in the other case the easy separation in
a certain direction is due to the mechanical arrangement of the coarse
sensible masses of stalks of hay.
In like manner I find that this piece of sandstone cleaves parallel to
the planes of bedding. This rock was once a powder, more or less coarse,
held in mechanical suspension by water. The powder was composed of two
distinct parts, fine grains of sand and small plates of mica. Imagine a
wide strand covered by a tide which holds such powder in suspension:[B]
how will it sink? The rounded grains of sand will reach the bottom
first, the mica afterwards, and when the tide recedes we have the little
plates shining like spangles upon the surface of the sand. Each
successive tide brings its charge of mixed powder, deposits its duplex
layer day after day, and finally masses of immense thickness are thus
piled up, which, by preserving the alternations of sand and mica, tell
the tale of their formation. I do not wish you to accept this without
proof. Take the sand and mica, mix them together in water, and allow
them to subside, they will arrange themselves in the manner I have
indicated; and by repeating the process you can actually build up a
sandstone mass which shall be the exact counterpart of that presented by
nature, as I have done in this glass jar. Now this structure cleaves
with readiness along the planes in which the particles of mica are
strewn. Here is a mass of such a rock sent to me from Halifax: here are
other masses from the quarries of Over Darwen in Lancashire. With a
hammer and chisel you see I can cleave them into flags; indeed these
flags are made use of for roofing purposes in the districts from which
the specimens have come, and receive the name of "slate-stone." But you
will discern, without a word from me, that this cleavage is not a
crystalline cleavage any more than that of a hayrick is. It is not an
arrangement produced by molecular forces; indeed it would be just as
reasonable to suppose that in this jar of sand and mica the particles
arranged themselves into layers by the forces of crystallization,
instead of by the simple force of gravity, as to imagine that such a
cleavage as this could be the product of crystallization.
This, so far as I am aware of, has never been imagined, and it has been
agreed among geologists not to call such splitting as this cleavage at
all, but to restrict the term to a class of phenomena which I shall now
proceed to consider.
Those who have visited the slate quarries of Cumberland and North Wales
will have witnessed the phenomena to which I refer. We have long drawn
our supply of roofing-slates from such quarries; schoolboys ciphered on
these slates, they were used for tombstones in churchyards, and for
billiard-tables in the metropolis; but not until a comparatively late
period did men begin to inquire how their wonderful structure was
produced. What is the agency which enables us to split Honister Crag, or
the cliffs of Snowdon, into laminæ from crown to base? This question is
at the present moment one of the greatest difficulties of geologists,
and occupies their attention perhaps more than any other. You may wonder
at this. Looking into the quarry of Penrhyn, you may be disposed to
explain the question as I heard it explained two years ago. "These
planes of cleavage," said a friend who stood beside me on the quarry's
edge, "are the planes of stratification which have been lifted by some
convulsion into an almost vertical position." But this was a great
mistake, and indeed here lies the grand difficulty of the problem. These
planes of cleavage stand in most cases at a high angle to the bedding.
Thanks to Sir Roderick Murchison, who has kindly permitted me the use of
specimens from the Museum of Practical Geology (and here I may be
permitted to express my acknowledgments to the distinguished staff of
that noble establishment, who, instead of considering me an intruder,
have welcomed me as a brother), I am able to place the proof of this
before you. Here is a mass of slate in which the planes of bedding are
distinctly marked; here are the planes of cleavage, and you see that one
of them makes a large angle with the other. The cleavage of slates is
therefore not a question of stratification, and the problem which we
have now to consider is, "By what cause has this cleavage been
produced?"
In an able and elaborate essay on this subject in 1835, Professor
Sedgwick proposed the theory that cleavage is produced by the action of
crystalline or polar forces after the mass has been consolidated. "We
may affirm," he says, "that no retreat of the parts, no contraction of
dimensions in passing to a solid state can explain such phenomena. They
appear to me only resolvable on the supposition that crystalline or
polar forces acted upon the whole mass simultaneously in one direction
and with adequate force." And again, in another place: "Crystalline
forces have rearranged whole mountain-masses, producing a beautiful
crystalline cleavage, passing alike through all the strata."[C] The
utterance of such a man struck deep, as was natural, into the minds of
geologists, and at the present day there are few who do not entertain
this view either in whole or in part.[D] The magnificence of the theory,
indeed, has in some cases caused speculation to run riot, and we have
books published, aye and largely sold, on the action of polar forces and
geologic magnetism, which rather astonish those who know something about
the subject. According to the theory referred to, miles and miles of the
districts of North Wales and Cumberland, comprising huge
mountain-masses, are neither more nor less than the parts of a gigantic
crystal. These masses of slate were originally fine mud; this mud is
composed of the broken and abraded particles of older rocks. It contains
silica, alumina, iron, potash, soda, and mica, mixed in sensible masses
mechanically together. In the course of ages the mass became
consolidated, and the theory before us assumes that afterwards a process
of crystallization rearranged the particles and developed in the mass a
single plane of crystalline cleavage. With reference to this hypothesis,
I will only say that it is a bold stretch of analogies; but still it has
done good service: it has drawn attention to the question; right or
wrong, a theory thus thoughtfully uttered has its value; it is a dynamic
power which operates against intellectual stagnation; and, even by
provoking opposition, is eventually of service to the cause of truth. It
would, however, have been remarkable, if, among the ranks of geologists
themselves, men were not found to seek an explanation of the phenomena
in question, which involved a less hardy spring on the part of the
speculative faculty than the view to which I have just referred.
The first step in an inquiry of this kind is to put oneself into contact
with nature, to seek facts. This has been done, and the labours of
Sharpe (the late President of the Geological Society, who, to the loss
of science and the sorrow of all who knew him, has so suddenly been
taken away from us), Sorby, and others, have furnished us with a body of
evidence which reveals to us certain important physical phenomena,
associated with the appearance of slaty cleavage, if they have not
produced it. The nature of this evidence we will now proceed to
consider.
Fossil shells are found in these slate-rocks. I have here several
specimens of such shells, occupying various positions with regard to the
cleavage planes. They are squeezed, distorted, and crushed. In some
cases a flattening of the convex shell occurs, in others the valves are
pressed by a force which acted in the plane of their junction, but in
all cases the distortion is such as leads to the inference that the rock
which contains these shells has been subjected to enormous pressure in a
direction at right angles to the planes of cleavage; the shells are all
flattened and spread out upon these planes. I hold in my hand a fossil
trilobite of normal proportions. Here is a series of fossils of the same
creature which have suffered distortion. Some have lain across, some
along, and some oblique to the cleavage of the slate in which they are
found; in all cases the nature of the distortion is such as required for
its production a compressing force acting at right angles to the planes
of cleavage. As the creatures lay in the mud in the manner indicated,
the jaws of a gigantic vice appear to have closed upon them and squeezed
them into the shape you see. As further evidence of the exertion of
pressure, let me introduce to your notice a case of contortion which
has been adduced by Mr. Sorby. The bedding of the rock shown in this
figure[E] was once horizontal; at A we have a deep layer of mud, and at
_m n_ a layer of comparatively unyielding gritty material; below that
again, at B, we have another layer of the fine mud of which slates are
formed. This mass cleaves along the shading lines of the diagram; but
look at the shape of the intermediate bed: it is contorted into a
serpentine form, and leads irresistibly to the conclusion that the mass
has been pressed together at right angles to the planes of cleavage.
This action can be experimentally imitated, and I have here a piece of
clay in which this is done and the same result produced on a small
scale. The amount of compression, indeed, might be roughly estimated by
supposing this contorted bed _m n_ to be stretched out, its length
measured and compared with the distance _c d_; we find in this way that
the yielding of the mass has been considerable.
Let me now direct your attention to another proof of pressure. You see
the varying colours which indicate the bedding on this mass of slate.
The dark portion, as I have stated, is gritty, and composed of
comparatively coarse particles, which, owing to their size, shape, and
gravity, sink first and constitute the bottom of each layer. Gradually
from bottom to top the coarseness diminishes, and near the upper surface
of each layer we have a mass of comparatively fine clean mud. Sometimes
this fine mud forms distinct layers in a mass of slate-rock, and it is
the mud thus consolidated from which are derived the German
razor-stones, so much prized for the sharpening of surgical instruments.
I have here an example of such a stone. When a bed is thin, the clean
white mud is permitted to rest, as in this case, upon a slab of the
coarser slate in contact with it: when the bed is thick, it is cut into
slices which are cemented to pieces of ordinary slate, and thus rendered
stronger. The mud thus deposited sometimes in layers is, as might be
expected, often rolled up into nodular masses, carried forward, and
deposited by the rivers from which the slate-mud has subsided. Here,
indeed, are such nodules enclosed in sandstone. Everybody who has
ciphered upon a school-slate must remember the whitish-green spots which
sometimes dotted the surface of the slate; he will remember how his
slate-pencil usually slid over such spots as if they were greasy. Now
these spots are composed of the finer mud, and they could not, on
account of their fineness, _bite_ the pencil like the surrounding gritty
portions of the slate. Here is a beautiful example of the spots: you
observe them on the cleavage surface in broad patches; but if this mass
has been compressed at right angles to the planes of cleavage, ought we
to expect the same marks when we look at the edge of the slab? The
nodules will be flattened by such pressure, and we ought to see evidence
of this flattening when we turn the slate edgeways. Here it is. The
section of a nodule is a sharp ellipse with its major axis parallel to
the cleavage. There are other examples of the same nature on the table;
I have made excursions to the quarries of Wales and Cumberland, and to
many of the slate-yards of London, but the same fact invariably appears,
and thus we elevate a common experience of our boyhood into evidence of
the highest significance as regards one of the most important problems
of geology. In examining the magnetism of these slates, I was led to
infer that these spots would contain a less amount of iron than the
surrounding dark slate. The analysis was made for me by Mr. Hambly in
the laboratory of Dr. Percy at the School of Mines. The result which is
stated in this Table justifies the conclusion to which I have referred.
_Analysis of Slate._
Purple Slate. Two Analyses.
1. Percentage of iron 5.85
2. " " 6.13
Mean 5.99
Greenish Slate.
1. Percentage of iron 3.24
2. " " 3.12
Mean 3.18
The quantity of iron in the dark slate immediately adjacent to the
greenish spot is, according to these analyses, nearly double of the
quantity contained in the spot itself. This is about the proportion
which the magnetic experiments suggested.
Let me now remind you that the facts which I have brought before you are
typical facts--each is the representative of a class. We have seen
shells crushed, the unhappy trilobites squeezed, beds contorted, nodules
of greenish marl flattened; and all these sources of independent
testimony point to one and the same conclusion, namely, that slate-rocks
have been subjected to enormous pressure in a direction at right angles
to the planes of cleavage.[F]
In reference to Mr. Sorby's contorted bed, I have said that by
supposing it to be stretched out and its length measured, it would give
us an idea of the amount of yielding of the mass above and below the
bed. Such a measurement, however, would not quite give the amount of
yielding; and here I would beg your attention to a point, the
significance of which has, so far as I am aware of, hitherto escaped
attention. I hold in my hand a specimen of slate, with its bedding
marked upon it; the lower portions of each bed are composed of a
comparatively coarse gritty material, something like what you may
suppose this contorted bed to be composed of. Well, I find that the
cleavage takes a bend in crossing these gritty portions, and that the
tendency of these portions is to cleave more at right angles to the
bedding. Look to this diagram: when the forces commenced to act, this
intermediate bed, which though comparatively unyielding is not entirely
so, suffered longitudinal pressure; as it bent, the pressure became
gradually more lateral, and the direction of its cleavage is exactly
such as you would infer from a force of this kind--it is neither quite
across the bed, nor yet in the same direction as the cleavage of the
slate above and below it, but intermediate between the two. Supposing
the cleavage to be at right angles to the pressure, this is the
direction which it ought to take across these more unyielding strata.
Thus we have established the concurrence of the phenomena of cleavage
and pressure--that they accompany each other; but the question still
remains, Is this pressure of itself sufficient to account for the
cleavage? A single geologist, as far as I am aware, answers boldly in
the affirmative. This geologist is Sorby, who has attacked the question
in the true spirit of a physical investigator. You remember the cleavage
of the flags of Halifax and Over Darwen, which is caused by the
interposition of plates of mica between the layers. Mr. Sorby examines
the structure of slate-rock, and finds plates of mica to be a
constituent. He asks himself, what will be the effect of pressure upon a
mass containing such plates confusedly mixed up in it? It will be, he
argues--and he argues rightly--to place the plates with their flat
surfaces more or less perpendicular to the direction in which the
pressure is exerted. He takes scales of the oxide of iron, mixes them
with a fine powder, and, on squeezing the mass, finds that the tendency
of the scales is to set themselves at right angles to the line of
pressure. Now the planes in which these plates arrange themselves will,
he contends, be those along which the mass cleaves.
I could show you, by tests of a totally different character from those
applied by Mr. Sorby, how true his conclusion is, that the effect of
pressure on elongated particles or plates will be such as he describes
it. Nevertheless, while knowing this fact, and admiring the ability with
which Mr. Sorby has treated this question, I cannot accept his
explanation of slate-cleavage. I believe that even if these plates of
mica were wholly absent, the cleavage of slate-rocks would be much the
same as it is at present.
I will not dwell here upon minor facts,--I will not urge that the
perfection of the cleavage bears no relation to the quantity of mica
present; but I will come at once to a case which to my mind completely
upsets the notion that such plates are a necessary element in the
production of cleavage.
Here is a mass of pure white wax: there are no mica particles here;
there are no scales of iron, or anything analogous mixed up with the
mass. Here is the self-same substance submitted to pressure. I would
invite the attention of the eminent geologists whom I see before me to
the structure of this mass. No slate ever exhibited so clean a cleavage;
it splits into laminæ of surpassing tenuity, and proves at a single
stroke that pressure is sufficient to produce cleavage, and that this
cleavage is independent of the intermixed plates of mica assumed in Mr.
Sorby's theory. I have purposely mixed this wax with elongated
particles, and am unable to say at the present moment that the cleavage
is sensibly affected by their presence,--if anything, I should say they
rather impair its fineness and clearness than promote it.
The finer the slate the more perfect will be the resemblance of its
cleavage to that of the wax. Compare the surface of the wax with the
surface of this slate from Borrodale in Cumberland. You have precisely
the same features in both: you see flakes clinging to the surfaces of
each, which have been partially torn away by the cleavage of the mass: I
entertain the conviction that if any close observer compares these two
effects, he will be led to the conclusion that they are the product of a
common cause.[G]
But you will ask, how, according to my view, does pressure produce this
remarkable result? This may be stated in a very few words.
Nature is everywhere imperfect! The eye is not perfectly achromatic, the
colours of the rose and tulip are not pure colours, and the freshest air
of our hills has a bit of poison in it. In like manner there is no such
thing in nature as a body of perfectly homogeneous structure. I break
this clay which seems so intimately mixed, and find that the fracture
presents to my eyes innumerable surfaces along which it has given way,
and it has yielded along these surfaces because in them the cohesion of
the mass is less than elsewhere. I break this marble, and even this wax,
and observe the same result: look at the mud at the bottom of a dried
pond; look to some of the ungravelled walks in Kensington Gardens on
drying after rain,--they are cracked and split, and other circumstances
being equal, they crack and split where the cohesion of the mass is
least. Take then a mass of partially consolidated mud. Assuredly such a
mass is divided and subdivided by surfaces along which the cohesion is
comparatively small. Penetrate the mass, and you will see it composed of
numberless irregular nodules bounded by surfaces of weak cohesion.
Figure to your mind's eye such a mass subjected to pressure,--the mass
yields and spreads out in the direction of least resistance;[H] the
little nodules become converted into laminæ, separated from each other
by surfaces of weak cohesion, and the infallible result will be that
such a mass will cleave at right angles to the line in which the
pressure is exerted.
Further, a mass of dried mud is full of cavities and fissures. If you
break dried pipe-clay you see them in great numbers, and there are
multitudes of them so small that you cannot see them. I have here a
piece of glass in which a bubble was enclosed; by the compression of the
glass the bubble is flattened, and the sides of the bubble approach each
other so closely as to exhibit the colours of thin plates. A similar
flattening of the cavities must take place in squeezed mud, and this
must materially facilitate the cleavage of the mass in the direction
already indicated.
Although the time at my disposal has not permitted me to develop this
thought as far as I could wish, yet for the last twelve months the
subject has presented itself to me almost daily under one aspect or
another. I have never eaten a biscuit during this period in which an
intellectual joy has not been superadded to the more sensual pleasure,
for I have remarked in all such cases cleavage developed in the mass by
the rolling-pin of the pastrycook or confectioner. I have only to break
these cakes, and to look at the fracture, to see the laminated structure
of the mass; nay, I have the means of pushing the analogy further: I
have here some slate which was subjected to a high temperature during
the conflagration of Mr. Scott Russell's premises. I invite you to
compare this structure with that of a biscuit; air or vapour within the
mass has caused it to swell, and the mechanical structure it reveals is
precisely that of a biscuit. I have gone a little into the mysteries of
baking while conducting my inquiries on this subject, and have received
much instruction from a lady-friend in the manufacture of puff-paste.
Here is some paste baked in this house under my own superintendence. The
cleavage of our hills is accidental cleavage, but this is cleavage with
intention. The volition of the pastrycook has entered into the formation
of the mass, and it has been his aim to preserve a series of surfaces of
structural weakness, along which the dough divides into layers.
Puff-paste must not be handled too much, for then the continuity of the
surfaces is broken; it ought to be rolled on a cold slab, to prevent the
butter from melting and diffusing itself through the mass, thus
rendering it more homogeneous and less liable to split. This is the
whole philosophy of puff-paste; it is a grossly exaggerated case of
slaty cleavage.
As time passed on, cases multiplied, illustrating the influence of
pressure in producing lamination. Mr. Warren De la Rue informs me that
he once wished to obtain white-lead in a fine granular state, and to
accomplish this he first compressed the mass: the mould was conical, and
permitted the mass to spread a little laterally under the pressure. The
lamination was as perfect as that of slate, and quite defeated him in
his effort to obtain a granular powder. Mr. Brodie, as you are aware,
has recently discovered a new kind of graphite: here is the substance in
powder, of exquisite fineness. This powder has the peculiarity of
clinging together in little confederacies; it cannot be shaken asunder
like lycopodium; and when the mass is squeezed, these groups of
particles flatten, and a perfect cleavage is produced. Mr. Brodie
himself has been kind enough to furnish me with specimens for this
evening's lecture. I will cleave them before you: you see they split up
into plates which are perpendicular to the line in which the pressure
was exerted. This testimony is all the more valuable, as the facts were
obtained without any reference whatever to the question of cleavage.
I have here a mass of that singular substance Boghead Cannel. This was
once a mass of mud, more or less resembling this one, which I have
obtained from a bog in Lancashire. I feel some hesitation in bringing
this substance before you, for, as in other cases, so in regard to
Boghead Cannel, science--not science, let me not libel it, but the
quibbling, litigious, money-loving portion of human nature speaking
through the mask of science--has so contrived to split hairs as to
render the qualities of the substance somewhat mythical. I shall
therefore content myself with showing you how it cleaves, and with
expressing my conviction that pressure had a great share in the
production of this cleavage.
The principle which I have enunciated is so simple as to be almost
trivial; nevertheless, it embraces not only the cases I have mentioned,
but, if time permitted, I think I could show you that it takes a much
wider range. When iron is taken from the puddling furnace, it is a more
or less spongy mass: it is at a welding heat, and at this temperature is
submitted to the process of rolling: bright smooth bars such as this are
the result of this rolling. But I have said that the mass is more or
less spongy or nodular, and, notwithstanding the high heat, these
nodules do not perfectly incorporate with their neighbours: what then?
You would say that the process of rolling must draw the nodules into
fibres--it does so; and here is a mass acted upon by dilute sulphuric
acid, which exhibits in a striking manner this fibrous structure. The
experiment was made by my friend Dr. Percy, without any reference to the
question of cleavage.
Here are other cases of fibrous iron. This fibrous structure is the
result of mechanical treatment. Break a mass of ordinary iron and you
have a granular fracture; beat the mass, you elongate these granules,
and finally render the mass fibrous. Here are pieces of rails along
which the wheels of locomotives have slidden; the granules have yielded
and become plates; they exfoliate or come off in leaves. All these
effects belong, I believe, to the great class of phenomena of which
slaty cleavage forms the most prominent example.[I]
Thus, ladies and gentlemen, we have reached the termination of our
task. I commenced by exhibiting to you some of the phenomena of
crystallization. I have placed before you the facts which are found to
be associated with the cleavage of slate-rocks. These facts, as finely
expressed by Helmholtz, are so many telescopes to our spiritual vision,
by which we can see backward through the night of antiquity, and discern
the forces which have been in operation upon the earth's surface
"Ere the lion roared,
Or the eagle soared."
From evidence of the most independent and trustworthy character, we come
to the conclusion that these slaty masses have been subjected to
enormous pressure, and by the sure method of experiment we have
shown--and this is the only really new point which has been brought
before you--how the pressure is sufficient to produce the cleavage.
Expanding our field of view, we find the self-same law, whose footsteps
we trace amid the crags of Wales and Cumberland, stretching its
ubiquitous fingers into the domain of the pastrycook and ironfounder;
nay, a wheel cannot roll over the half-dried mud of our streets without
revealing to us more or less of the features of this law. I would say,
in conclusion, that the spirit in which this problem has been attacked
by geologists indicates the dawning of a new day for their science. The
great intellects who have laboured at geology, and who have raised it to
its present pitch of grandeur, were compelled to deal with the subject
in mass; they had no time to look after details. But the desire for more
exact knowledge is increasing; facts are flowing in, which, while they
leave untouched the intrinsic wonders of geology, are gradually
supplanting by solid truths the uncertain speculations which beset the
subject in its infancy. Geologists now aim to imitate, as far as
possible, the conditions of nature, and to produce her results; they are
approaching more and more to the domain of physics; and I trust the day
will soon come when we shall interlace our friendly arms across the
common boundary of our sciences, and pursue our respective tasks in a
spirit of mutual helpfulness, encouragement, and good-will.
FOOTNOTES:
[A] Referred to in the Introduction.
[B] I merely use this as an illustration; the deposition may have really
been due to sediment carried down by rivers. But the action must have
been periodic, and the powder duplex.
[C] 'Transactions of the Geological Society,' Ser. ii. vol. iii. p. 477.
[D] In a letter to Sir Charles Lyell, dated from the Cape of Good Hope,
February 20, 1836, Sir John Herschel writes as follows:--"If rocks have
been so heated as to allow of a commencement of crystallization, that is
to say, if they have been heated to a point at which the particles can
begin to move amongst themselves, or at least on their own axes, some
general law must then determine the position in which these particles
will rest on cooling. Probably that position will have some relation to
the direction in which the heat escapes. Now when all or a majority of
particles of the same nature have a general tendency to one position,
that must of course determine a cleavage plane."
[E] Omitted here.
[F] While to my mind the evidence in proof of pressure seems perfectly
irresistible, I by no means assert that the manner in which I stated it
is incapable of modification. All that I deem important is the fact that
pressure has been exerted; and provided this remain firm, the fate of
any minor portion of the evidence by which it is here established is of
comparatively little moment.
[G] I have usually softened the wax by warming it, kneaded it with the
fingers, and pressed it between thick plates of glass previously wetted.
At the ordinary summer-temperature the wax is soft, and tears rather
than cleaves; on this account I cool my compressed specimens in a
mixture of pounded ice and salt, and when thus cooled they split
beautifully.
[H] It is scarcely necessary to say that if the mass were squeezed
equally in _all_ directions no laminated structure could be produced; it
must have room to yield in a lateral direction.
[I] An eminent authority informs me that he believes these surfaces of
weak cohesion to be due to the interposition of films of graphite, and
not to any tendency of the iron itself to become fibrous: this of course
does not in any way militate against the theory which I have ventured to
propose. All that the theory requires is surfaces of weak cohesion,
however produced, and a change of shape of such surfaces consequent on
pressure or rolling.
INDEX.
Æggischhorn, 100, 105.
Agassiz on glacier motion, 270, 310.
Air-bubbles, 359, 376.
Aletsch Glacier, 101.
-- --, bedding and structure observed on, 120, 391.
Aletschhorn, cloud iridescences on, 100, 238.
Allalein Glacier, 162.
Alpine climbers, suggestions to, 169.
Alps, winter temperature of, 168.
Altmann's theory of glacier motion, 296.
Ancient glaciers, action of, 99, 141.
Arveiron, arch of, 38, 217.
Atmosphere, permeability of, to radiant heat, 105, 243-247.
Atmospheric refraction, 35.
Avalanche at Saas, 164.
--, sound of, explained, 12, 14.
Bakewell, Mr., on motion of Glacier des Bossons, 337.
Balmat, Auguste, 169, 188.
Bedding, lines of, 391.
Bennen, Johann Joseph, 104, 118.
Bergschrund, 98, 325.
"Blower," glacier, 87.
Blue colour of ice, 256.
-- -- -- snow, 29, 83, 132, 203.
-- -- -- water, 33, 253, 259-262.
Blueness of sky, 22, 174, 257-261.
Blue veins, 376, 381.
Boiling-point, influence of pressure on, 408.
-- -- at different altitudes, 105, 106, 113, 120, 129, 175, 190.
Bois, Glacier des, 39, 275, 368.
Brévent, ascent of, 172.
Brocken, Spirit of the, 22, 238.
Bubbles, in ice, 44, 147, 359, 425.
-- in snow, 18, 251.
Capillaries of glacier, 335-339.
Cave of ice, 135.
Cavities in ice, 163, 356, 424.
Cells in ice, 147, see Bubbles.
Chamouni, 37.
--, difficulties at, 170, 192.
-- in winter, 198, 336.
Charmoz, view from, 45, 68, 368.
Charpentier's theory of glacier motion, 296.
Chemical action, rays producing, 240.
Chromatic effects, 235.
Cleavage, 406.
-- and stratification distinct, 2, 390, 431.
-- caused by pressure, 6, 436.
--, contortions of, 9, 59.
-- of crystals and slate rocks, lecture on, 427.
-- of glaciers, 26, 393, 425-426.
-- -- ice, 352, 407.
-- -- slate, &c., 1, 430.
"Cleft station," the, 47, 369.
Clouds, formation and dissipation of, 22, 97, 137, 146.
--, iridescent, 100, 105, 147, 154, 238.
-- on Mont Blanc, 82.
-- on Monte Rosa, 124.
--, winter, at Montanvert, 208.
Colour answers to pitch, 227.
Colours of sky, 257.
--, subjective, 37.
Comet, discovery of, 186.
Compass affected by rocks, 140.
Crepitation of glaciers, 44, 357.
Crevasses, 315
(_marginal_, 318;
_transverse_, 320;
_longitudinal_, 322), 424.
--, first opening of, 317, 327.
Crumples in ice, 174, 415, 419.
Crystallization of ice, 353.
Crystals, cleavage of, 3, 428.
-- of snow, 130, 205, 212.
Deafness, artificial, 167.
Differential motion, 395.
-- --, Dr. Whewell on, 396.
Diffraction, explanation of, 237.
Dirt-bands, 45, 46, 68, 95, 367, 373.
-- --, maps of, 367, 368, 369.
-- --, Forbes on, 371.
-- --, source of, 369, 425.
Disks in ice, planes of, 163, 358, 425.
Dollfuss, M., hut of, 18, 112.
Dôme du Goûter, 68, 75.
Donny, M., on cohesion of liquids, 355.
Echoes, theory of, 15.
Eismeer, the, 13, 362.
Expedition of 1856, Oberland and Tyrol, 9-32.
-- -- 1857, Montanvert and Mer de Glace, 33-91.
-- -- 1858, Oberland, Valais, and Monte Rosa district, 92-192.
-- -- 1859, winter, Chamouni, and Mer de Glace, 195-219.
Faraday, Prof., on Regelation, 351.
Faulberg, cave of, 107.
Fée, glacier of, 165.
Fend, 32.
Finsteraarhorn, 104, 110.
--, summit of, 112.
Flowers, liquid, in ice, 147, 354-358, 424.
Forbes, Prof., comparison of glacier to river, 306, 308.
-- --, on glacier motion, 272, 304, 308.
-- --, on magnetism of rocks, 145.
-- --, on veined structure, 379.
-- --, viscous theory, 311, 327, 333, 335.
Freezing, planes of, 163, 358, 424.
Frost-bites, 191.
Frozen flowers, 130, 212.
Furgge glacier, structure crossing strata on, 160, 392-394.
Gases, passage of heat through, 243.
Géant, Col du, 50, 173.
Géant, glacier du, 53-57, 280, 369-373.
--, measurements on, 419-421.
--, motion of, 281, 286.
--, white ice seams of, 56, 413.
Gebatsch Alp, 23.
--, glacier of, 24, 26.
Geneva, Lake of, 33, 259-262.
Glaciers, ancient, action of, 99, 163.
-- "blower," 87.
--, capillaries of, 335-339.
--, crepitation of, 44, 357.
-- d'écoulement, 301.
-- de Léchaud, see Léchaud.
-- des Bois, 39, 275, 368.
-- du Géant, see Géant.
-- du Talèfre, see Talèfre.
--, groovings on, 20, 56, 377.
--, measurement of, 276.
-- motion, 52, 269-295, 422.
-- --, earlier theories of, 296-314.
-- --, pressure theory of, 346.
--, origin of, 248-252.
-- réservoirs, 301.
--, ridges on, 42, 55.
--, structure of, 136, 148, see Veined structure.
-- tables, 44, 265.
--, veins of, 54, 376, 381.
--, wrinkles on, 370.
Goethe's theory of colours, 258.
Görner glacier, 120, 138.
Görner grat, 137, 145.
Görnerhorn glacier, 147, 149.
Grand Plateau, 187.
Grands Mulets, 73, 185.
Graun, 29.
Grimsel, the, 18, 99.
Grindelwald, lower glacier of, 13, 92, 321, 384.
Groovings on glaciers, 20, 56, 377.
Grüner's theory of glacier motion, 296.
Guides of Chamouni, rules of, 60, 170, 192.
-- lost in crevasse, 76.
Guyot, M., on veined structure, 378.
Hailstones, conical, 31.
--, spherical, 65.
Handeck, waterfall of, 17.
Hasli, valley of, 17, 99.
Heat and light, 223, 239, 241.
-- -- work, 328.
--, luminous, 241-247.
--, mechanical equivalent of, 329.
--, obscure, 240.
--, passage through gases, 243-245.
--, radiant, 239.
-- --, permeability of atmosphere to, 105, 243-247.
--, radiated, 242.
--, specific, 331.
Heisse Platte, the, 13.
Hirst, Mr., measurements on Mer de Glace, 38, 46, 275, 283, 289, 313,
420.
Hochjoch, 32.
Höchste Spitze of Monte Rosa, 128.
Hopkins, Mr., on crevasses, 318, 383.
Hôtel des Neufchâtelois, 19, 112, 270.
Hugi on glacier motion, 270.
Huxley, Mr., on glacier capillaries, 338.
-- --, on water-cells, 251, 359.
Hydrogen, effect on rays, 253.
Ice, blue colour of, 256.
-- cascades, 94, 384, 391.
-- cave, 135.
-- cells, 147, see Bubbles.
-- cones, 266.
--, cracking of, 317, 326.
--, crystallization of, 353.
--, effects of pressure on, 405, 409.
--, experiments on, 346.
--, friability of, 333.
--, liquefaction of, 353, 408.
--, liquid flowers in, 354-358, 424.
--, Thomson's theory of plasticity of, 340.
--, softening of, 333.
--, structure of, 136, 148.
--, temperature of, 241, 332.
--, white, seams of, 56, 413, 421.
Illumination of trees, &c., at sunrise and sunset, 178, 238.
Interference rings, 229.
-- spectra, 76, 178, 235, 238.
Iridescent clouds, 100, 105, 147, 154, 238.
Jardin, the, 61, 174.
Joch, the passage of a, 28.
Joule, M., on heat and work, 328.
Jungfrau, the, 11.
--, evening near, 106.
Laminated structure, 376, 378, 426.
Léchaud, glacier de, 53, 387.
-- -- --, motion of, 60, 286-288.
Lenticular structure, 381.
Light and heat, 223, 239, 241.
--, undulation theory of, 224.
Linth, M. Escher de la, 271.
Liquefaction of ice, 353, 408.
Liquid flowers, 147, 354-358, 424.
Magnetic force, 144.
Magnetism of rocks, 140, 143, 145.
Märjelen See, 101, 119.
Mastic, Brücke's solution of, 259.
Mattmark See, 162.
Maximum motion, locus of point of, 285, 323.
Mayenwand, summit of, 20, 100, 323.
Mayer, on connexion of heat with work, 328.
Measurement of glaciers, 276.
Mer de Glace, 42-67, 86-90, 173.
-- -- --, dirt-bands of the, 367
(seen from Charmoz, 45, 368;
from Cleft station, 47, 369;
from the Flégère, 367).
-- -- --, map of, 53, 264.
-- -- --, motion of, 275-293.
-- -- --, winter motion of, 294, 343.
-- -- --, winter visit to, 195, 206-218.
Milk, cause of blueness of, 261.
Mirage, 36.
Montanvert, 40, 89, 173.
-- in winter, 204.
Mont Blanc, first ascent of, 68.
-- --, second ascent of, 177.
-- --, summit of, 81, 189.
Monte Rosa, first ascent of, 122.
-- --, second ascent of, 151.
-- --, summit of, 128, 156.
-- --, western glacier of, 138, 147.
-- --, zones of colour, 154, 238.
Moraines, 263.
-- of Talèfre, 54, 63, 267, 387.
Motion of glaciers, 52, 269-295, 422.
Moulins, 362, 424.
--, depth of, 365.
--, motion of, 364.
Necker, letter from, 178.
Neufchâtelois, Hôtel des, 19, 112, 270.
Névé ice, 249, 251.
Oberland, the, visited, 9-22; 92-120; 390.
Oils, effect of films of, 236.
Person, M., on softening of ice, 333.
Pistol fired on summit of Mont Blanc, 82, 83, 224.
Pitch of musical sounds, 225.
Planes of freezing, 163, 358, 424.
Plasticity of ice, Thomson's theory of, 340.
Polar forces, 4.
Pressure and cleavage, see Cleavage.
-- and liquefaction of ice, 340, 408.
-- -- veined structure, 404; 147-149, 382-394, 412, 425-426.
--, effects of, on boiling point, 408.
-- -- -- -- ice, 405, 409.
-- theory of glacier motion, 346.
Radiant heat, 105, 239.
Rays, calorific, 240.
--, transmission of, 242.
Redness of sunset, 175.
Refraction on lake of Geneva, 35.
Regelation, 347, 351.
Reichenbach fall, 17.
Rendu, comparison of glacier to river, 306.
--, measurements of glaciers, 304.
--, notice of regelation, 301.
-- on conversion of snow into ice, 301.
-- on ductility, 298.
-- on law of circulation, 300.
-- on motion of glaciers, 305.
-- on veined structure, 301.
-- theory of glaciers, 299.
Rhone at lake of Geneva, 34, 261.
-- glacier, 20, 100, 323, 386.
-- --, chromatic effects, 21, 238.
Ridges on glaciers, 42, 55.
Riffelhorn, the, 133, 141-145.
Rings, interference, 229.
-- round sun, 21, 238.
Ripples deduced from rings, 400.
Ripple theory, Forbes on, 398.
-- -- of veined structure, 398.
-- waves, movement of, 232.
River and glacier, analogies between, 281-285, 423; 368.
Rocks, magnetism of, 140, 143, 145.
Saas, avalanche at, 164.
Sabine, Gen., on veined structure, 378.
Sand-cones, 266.
Saussure's theory of glacier motion, 52, 296.
Scheuchzer's theory of glacier motion, 296.
Seams, white, in ice, 56, 88, 413, 421.
Sedgwick, Prof., on cleavage, 2-5, 390, 431.
Séracs, 51, 75.
Serpentine, boulders of, 161.
Shadows, coloured, 38.
Sharpe, on slaty cleavage, 5, 432.
Silberhorn, the, 11.
Sky, blueness of, 22, 174, 175.
--, colours of, explained, 257.
Slate, cleavage of, 1, 430.
Snow, blue colour of, 29, 132, 203.
-- crystals, 130, 205, 212.
--, dry, 250.
-- line, 29, 248.
--, perpetual, 248.
--, sound of breaking, 202.
-- storm, sound through, 215.
--, whiteness of, explained, 250.
Sorby, Mr., on slaty cleavage, 5, 435.
Sound in a vacuum, 224.
--, intensity of, 83.
--, rate of motion of, 226.
Spectra, interference, 76, 178, 235, 238.
Spectrum, rays of, 240.
Stars, twinkling of, 72, 238.
Stelvio, pass of, 29.
Storm on Grands Mulets, 185.
-- -- Mer de Glace, 210.
Strahleck, glacier of, 94, 384.
--, passage of, 93, 97.
Strata of ice, 136.
Stratification of névé, 392.
-- -- slate, 1, 430.
Structure, doubts regarding, 44, 92, 389.
-- of ice, 136, 148, see Veined structure.
Subjective colours, 37.
Summary of glacier theory, 422.
Sun, rings round, 21, 238.
Sunrise at Chamouni, 39.
-- and sunset, illumination of trees, &c., at, 178, 238.
Sunset, gorgeous, 184.
Tables, glacier, 44, 265-266.
Tacul, motion of ice-wall at, 289.
Talèfre, glacier of, 43, 61-62, 87.
--, moraines of, 54, 63, 267, 387.
Temperature, winter, of Alps, 168.
Theodolite, use of, 275.
Theory of cleavage, 5.
Thermometer at Jardin, 174.
-- buried on Mont Blanc, 190.
-- on Finsteraarhorn, 113.
Thomson, Prof., theory of plasticity, 340.
-- -- -- -- regelation, 352.
Twinkling of stars, 72, 238.
Tyrol, the, 23.
Undulation theory of light, 224.
Unteraar, glacier of, 18, 265, 388.
Vacuum in ice-cavities, 163, 356.
Veined structure, 376
(_marginal_, 383;
_transverse_, 384;
_longitudinal_, 387), 395, 404, 408.
-- --, experiments on, 382, 388.
-- -- caused by pressure, 147-149, 382-389, 412, 425-426.
-- -- crossing strata, 389-394.
-- --, Forbes on, 379.
-- --, Gen. Sabine on, 378.
-- --, M. Guyot on, 378.
-- --, ripple theory of, 398.
Viesch, glacier of, 109, 118.
Viscosity, 312, 325, 334, 350, 423.
Water absorbs red rays, 254.
--, blue colour of, 254; 33, 259, 261.
--, rippling waves of, 232.
Waves, frozen, 43, 55.
--, interference of, 231.
-- motion, Weber on, 232, 399.
-- of sound, 225.
Wengern Alp, 9.
Wetterhorn, echoes of, 15.
White ice, seams of, 56, 57, 88, 413, 421.
Whiteness of ice, 250, 268, 376.
Winter motion of Mer de Glace, 294.
Wrinkles on glacier, 370.
Young, Thomas, theory of light, 224.
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Transcriber's Notes.
The titles from the List of Illustrations were copied to the captions of
the figures that otherwise had no caption, for the convenience of the
reader.
The "sidenotes" in the main body of the text were originally page
headers. They have been moved to a place more fitting for the flow,
typically to the head of the appropriate paragraph.
Spelling variants where there was no obviously preferred choice were
retained. These include: "Cleft-Station" and "Cleft Station," plus
variants; "Cima di Jazzi" and "Cima de Jazzi;" "fanlike" and "fan-like;"
"firewood" and "fire-wood;" "Flégère" and "Flegère;" "foreshorten(ed)"
and "fore-shorten(ing);" "generalisation" and "generalization;"
"judgment" and "judgement;" "Kumm" and "Kumme," which may be the same as
"Kamm;" "lime light" and "lime-light;" "realize" and "realise(d);"
"recognise" and "recognize(d);" "rearranged" and "re-arranged;"
"refrozen" and "re-frozen;" "self-same" and "selfsame;" "semifluid" and
"semi-fluid;" "sundial" and "sun-dial;" "Trift" and "Trifti," probably
the same glacier; "weatherworn" and "weather-worn."
In the Latin-1 encoded text version, the oe-ligature was replaced by
the two separate characters, "oe."
Changed "Hockjoch" to "Hochjoch" on page xi: "passage of the Hochjoch."
Changed "39" to "239" on page xvii, as the page number for chapter 2.
Changed "icefall" to "ice-fall" on page xxvi: "part of ice-fall."
Changed "havresack" to "haversack" on page 71: "my waterproof
haversack."
Changed "afflùent" to "affluent" on page 98: "Finsteraar affluent."
Changed "184°.92" to "184.92°" on page 129.
Changed "gulleys" to "gullies" on page 143: "fissures and gullies."
Changed "SNOWSTORM" to "SNOW-STORM" in the sidenote from page 215:
"SOUND THROUGH THE SNOW-STORM."
Changed "neutralise" to "neutralize" on page 231: "oppose and
neutralize."
Moved the semi-colon inside the double quotes on page 285, around:
"corresponding points."
Changed "THOMPSON'S" to "THOMSON'S" in the chapter heading on page 340:
"THOMSON'S THEORY."
Changed "last" to "least" in the footnote to page 292: "at least as
anxious."
Changed "I" to "It" on page 377: "It was also."
"Die Gletscher der Jetzzeit" on page 393 should probably be "Die
Gletscher der Jetztzeit," but was not changed.
Inserted a comma in the index entry for "Aletsch Glacier:" "-- --,
bedding."
Inserted a comma in the index entry for "Dirt-bands:" "-- --, maps of."
Changed "Goutér" to "Goûter" in the index entry for "Dôme du Goûter."
Changed "Hoch-joch" to "Hochjoch" in its index entry.
Inserted second em-dash in the index entry for "Mont Blanc:" "-- --,
second ascent of."
Inserted a comma in the index entry for "Rays:" "--, transmission of."
Inserted a comma in the index entry for "Strahleck:" "--, passage of."
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