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Title: Through Magic Glasses and Other Lectures
A Sequel to The Fairyland of Science
Author: Arabella B. Buckley
Release Date: October 1, 2011 [eBook #37589]
Language: English
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[Illustration: For Description see Page 152 Frontispiece
THE GREAT NEBULA OF ORION
From a photograph taken on February 4th, 1889 by Mr Isaac Roberts.]
THROUGH MAGIC GLASSES AND OTHER LECTURES
A Sequel to The Fairyland of Science
by
ARABELLA B. BUCKLEY
(Mrs. Fisher)
Author of Life and Her Children, Winners in Life's Race,
A Short History of Natural Science, Etc.
With Numerous Illustrations
New York
D. Appleton and Company
1890
Authorized Edition.
PREFACE.
The present volume is chiefly intended for those of my young friends who
have read, and been interested in, the _Fairyland of Science_. It
travels over a wide field, pointing out a few of the marvellous facts
which can be studied and enjoyed by the help of optical instruments. It
will be seen at a glance that any one of the subjects dealt with might
be made the study of a lifetime, and that the little information given
in each lecture is only enough to make the reader long for more.
In these days, when moderate-priced instruments and good books and
lectures are so easily accessible, I hope some eager minds may be thus
led to take up one of the branches of science opened out to us by magic
glasses; while those who go no further will at least understand
something of the hitherto unseen world which is now being studied by
their help.
The two last lectures wander away from this path, and yet form a natural
conclusion to the Magician's lectures to his young Devonshire lads. They
have been published before, one in the _Youth's Companion_ of Boston,
U.S., and the other in _Atalanta_, in which the essay on Fungi also
appeared in a shorter form. All three lectures have, however, been
revised and fully illustrated, and I trust that the volume, as a whole,
may prove a pleasant Christmas companion.
For the magnificent photograph of Orion's nebula, forming the
Frontispiece, I am indebted to the courtesy of Mr. Isaac Roberts,
F.R.A.S., who most kindly lent me the plate for reproduction; and I have
had the great good fortune to obtain permission from MM. Henri of the
Paris Observatory to copy the illustration of the Lunar Apennines from a
most beautiful and perfect photograph of part of the moon, taken by them
only last March. My cordial thanks are also due to Mr. A. Cottam,
F.R.A.S., for preparing the plate of coloured double stars, and to my
friend Mr. Knobel, Hon. Sec. of the R.A.S., for much valuable
assistance; to Mr. James Geikie for the loan of some illustrations from
his _Geology_; and to Messrs. Longman for permission to copy Herschel's
fine drawing of Copernicus.
With the exception of these illustrations and a few others, three of
which were kindly given me by Messrs. Macmillan, all the woodcuts have
been drawn and executed under the superintendence of Mr. Carreras, jun.,
who has made my task easier by the skill and patience he has exercised
under the difficulties incidental to receiving instructions from a
distance.
ARABELLA B. BUCKLEY.
UPCOTT AVENEL, _Oct. 1890_.
TABLE OF CONTENTS
CHAPTER I PAGE
THE MAGICIAN'S CHAMBER BY MOONLIGHT 1
CHAPTER II
MAGIC GLASSES AND HOW TO USE THEM 27
CHAPTER III
FAIRY RINGS AND HOW THEY ARE MADE 55
CHAPTER IV
THE LIFE-HISTORY OF LICHENS AND MOSSES 75
CHAPTER V
THE HISTORY OF A LAVA STREAM 96
CHAPTER VI
AN HOUR WITH THE SUN 117
CHAPTER VII
AN EVENING AMONG THE STARS 145
CHAPTER VIII
LITTLE BEINGS FROM A MINIATURE OCEAN 172
CHAPTER IX
THE DARTMOOR PONIES 195
CHAPTER X
THE MAGICIAN'S DREAM OF ANCIENT DAYS 209
LIST OF ILLUSTRATIONS
PLATES
PHOTOGRAPH OF THE NEBULA OF ORION _Frontispiece_
TABLE OF COLOURED SPECTRA Plate I. _facing p._ 127
COLOURED DOUBLE STARS Plate II. _facing p._ 167
WOODCUTS IN THE TEXT PAGE
PARTIAL ECLIPSE OF THE MOON _Initial letter_ 1
A BOY ILLUSTRATING THE PHASES OF THE MOON 6
COURSE OF THE MOON IN THE HEAVENS 8
CHART OF THE MOON 10
FACE OF THE FULL MOON 11
TYCHO AND HIS SURROUNDINGS (from a photograph by De la Rue) 13
PLAN OF THE PEAK OF TENERIFFE 15
THE CRATER COPERNICUS 17
THE LUNAR APPENNINES (from a photograph by M.M. Henri) 19
THE CRATER PLATO SEEN SOON AFTER SUNRISE 20
DIAGRAM OF TOTAL ECLIPSE OF THE MOON 23
BOY AND MICROSCOPE _Initial letter_ 27
EYE-BALL SEEN FROM THE FRONT 30
SECTION OF AN EYE LOOKING AT A PENCIL 31
IMAGE OF A CANDLE-FLAME THROWN ON PAPER BY A LENS 33
ARROW MAGNIFIED BY A CONVEX LENS 35
STUDENT'S MICROSCOPE 36
SKELETON OF A MICROSCOPE 37
FOSSIL DIATOMS SEEN UNDER THE MICROSCOPE 39
AN ASTRONOMICAL TELESCOPE 41
TWO SKELETONS OF TELESCOPES 44
THE PHOTOGRAPHIC CAMERA 47
KIRCHHOFF'S SPECTROSCOPE 51
PASSAGE OF RAYS THROUGH THE SPECTROSCOPE 52
A GROUP OF FAIRY-RING MUSHROOMS _Initial letter_ 55
THREE FORMS OF VEGETABLE MOULD MAGNIFIED 61
_MUCOR MUCEDO_ GREATLY MAGNIFIED 63
YEAST CELLS GROWING UNDER THE MICROSCOPE 65
EARLY STAGES OF THE MUSHROOM 67
LATER STAGES OF THE MUSHROOM 68
MICROSCOPIC STRUCTURE OF MUSHROOM GILLS 69
A GROUP OF CUP LICHENS _Initial letter_ 75
EXAMPLES OF LICHENS FROM LIFE 77
SINGE-CELLED PLANTS GROWING 78
SECTIONS OF LICHENS 81
FRUCTIFICATION OF A LICHEN 83
A STEM OF FEATHERY MOSS FROM LIFE 85
MOSS-LEAF MAGNIFIED 87
_POLYTRICHUM COMMUNE_, A LARGE HAIR-MOSS 88
FRUCTIFICATION OF A MOSS 89
SPHAGNUM MOSS FROM A DEVONSHIRE BOG 93
SURFACE OF A LAVA-FLOW _Initial letter_ 96
VESUVIUS AS SEEN IN ERUPTION 97
TOP OF VESUVIUS IN 1864 100
DIAGRAMMATIC SECTION OF AN ACTIVE VOLCANO 105
SECTION OF A LAVA-FLOW 108
VOLCANIC GLASS WITH CRYSTALLITES AND MICROLITHS 109
VOLCANIC GLASS WITH WELL-DEVELOPED MICROLITHS 110
A PIECE OF DARTMOOR GRANITE 112
VOLCANIC GLASS SHOWING LARGE INCLUDED CRYSTALS 115
A TOTAL ECLIPSE OF THE SUN _Initial letter_ 117
FACE OF THE SUN PROJECTED ON A PIECE OF CARDBOARD 120
PHOTOGRAPH OF THE SUN'S FACE, taken by Mr. Selwyn
(Secchi, _Le Soleil_) 122
TOTAL ECLIPSE OF THE SUN, SHOWING CORONA AND PROMINENCES
(Guillemin, _Le Ciel_) 124
KIRCHHOFF'S EXPERIMENT ON THE DARK SODIUM LINE 128
THE SPECTROSCOPE ATTACHED TO THE TELESCOPE FOR SOLAR WORK 132
SUN-SPECTRUM AND PROMINENCE SPECTRUM COMPARED 134
RED PROMINENCES, as drawn by Mr. Lockyer 1869 136
A QUIET SUN-SPOT 140
A TUMULTUOUS SUN-SPOT 141
A STAR-CLUSTER _Initial letter_ 145
SOME CONSTELLATIONS SEEN ON LOOKING SOUTH IN MARCH FROM
SIX TO NINE O'CLOCK 148
THE CHIEF STARS OF ORION, WITH ALDEBARAN 149
THE TRAPEZIUM [Greek: th] ORIONIS 150
SPECTRUM OF ORION'S NEBULA AND SUN-SPECTRUM COMPARED 151
SOME CONSTELLATIONS SEEN ON LOOKING NORTH IN MARCH FROM
SIX TO NINE O'CLOCK 156
THE GREAT BEAR, SHOWING POSITION OF THE BINARY STAR 157
DRIFTING OF THE SEVEN STARS OF CHARLES'S WAIN 159
CASSIOPEIA AND THE HEAVENLY BODIES NEAR 162
[Greek: e] LYRÆ, A DOUBLE-BINARY STAR 166
A SEASIDE POOL _Initial letter_ 172
A GROUP OF SEAWEEDS (natural size) 175
_ULVA LACTUCA_, a piece greatly magnified 176
SEAWEEDS, magnified to show fruits 177
A CORALLINE AND SERTULARIAN COMPARED 179
_SERTULARIA TENELLA_ HANGING IN WATER 180
_THURICOLLA FOLLICULATA_ AND _CHILOMONAS AMYGDALUM_ 182
A GROUP OF LIVING DIATOMS 184
A DIATOM GROWING 185
_CYDIPPE PILEUS_, ANIMAL AND STRUCTURE 187
THE SEA-MAT, _FLUSTRA FOLIACEA_ 191
DIAGRAM OF THE FLUSTRA ANIMAL 192
DARTMOOR PONIES _Initial letter_ 195
_EQUUS HEMIONUS_, THE HORSE-ASS OF TARTARY AND TIBET 201
PRZEVALSKY'S WILD HORSE 202
SKELETON OF AN ANIMAL OF THE HORSE-TRIBE 206
PALÆOLITHIC MAN CHIPPING FLINT TOOLS _Initial letter_ 209
SCENE IN PALÆOLITHIC TIMES 212
PALÆOLITHIC RELICS--NEEDLE, TOOTH, IMPLEMENT 213
MAMMOTH ENGRAVED ON IVORY 216
NEOLITHIC IMPLEMENTS--HATCHET, CELT, SPINDLE WHORL 219
A BURIAL IN NEOLITHIC TIMES 221
BRITISH RELICS--COIN, BRONZE CELT, AND BRACELET 223
BRITONS TAKING REFUGE IN THE CAVE 224
THROUGH MAGIC GLASSES
CHAPTER I
THE MAGICIAN'S CHAMBER BY MOONLIGHT
[Illustration]
The full moon was shining in all its splendour one lovely August night,
as the magician sat in his turret chamber bathed in her pure white
beams, which streamed upon him through the open shutter in the wooden
dome above. It is true a faint gleam of warmer light shone from below
through the open door, for this room was but an offshoot at the top of
the building, and on looking down the turret stairs a lecture-room might
be seen below where a bright light was burning. Very little, however, of
this warm glow reached the magician, and the implements of his art
around him looked like weird gaunt skeletons as they cast their long
shadows across the floor in the moonlight.
The small observatory, for such it was, was a circular building with
four windows in the walls, and roofed with a wooden dome, so made that
it could be shifted round and round by pulling certain cords. One
section of this dome was a shutter, which now stood open, and the strip,
thus laid bare to the night, was so turned as to face that part of the
sky along which the moon was moving. In the centre of the room, with its
long tube directed towards the opening, stood the largest magic glass,
the TELESCOPE, and in the dead stillness of the night, could be heard
distinctly the tick-tick of the clockwork, which kept the instrument
pointing to the face of the moon, while the room, and all in it, was
being carried slowly and steadily onwards by the earth's rotation on its
axis. It was only a moderate-sized instrument, about six feet long,
mounted on a solid iron pillar firmly fixed to the floor and fitted with
the clockwork, the sound of which we have mentioned; yet it looked like
a giant as the pale moonlight threw its huge shadow on the wall behind
and the roof above.
Far away from this instrument in one of the windows, all of which were
now closed with shutters, another instrument was dimly visible. This was
a round iron table, with clawed feet, and upon it, fastened by screws,
were three tubes, so arranged that they all pointed towards the centre
of the table, where six glass prisms were arranged in a semicircle, each
one fixed on a small brass tripod. A strange uncanny-looking instrument
this, especially as the prisms caught the edge of the glow streaming up
the turret stair, and shot forth faint beams of coloured light on the
table below them. Yet the magician's pupils thought it still more
uncanny and mysterious when their master used it to read the alphabet of
light, and to discover by vivid lines even the faintest trace of a metal
otherwise invisible to mortal eye.
For this instrument was the SPECTROSCOPE, by which he could break up
rays of light and make them tell him from what substances they came.
Lying around it were other curious prisms mounted in metal rims and
fitted with tubes and many strange devices, not to be understood by the
uninitiated, but magical in their effect when fixed on to the telescope
and used to break up the light of distant stars and nebulæ.
Compared with these mysterious glasses the PHOTOGRAPHIC CAMERA, standing
in the background, with its tall black covering cloth, like a hooded
monk, looked comparatively natural and familiar, yet it, too, had
puzzling plates and apparatus on the table near it, which could be
fitted on to the telescope, so that by their means pictures might be
taken even in the dark night, and stars, invisible with the strongest
lens, might be forced to write their own story, and leave their image on
the plate for after study.
All these instruments told of the magician's power in unveiling the
secrets of distant space and exploring realms unknown, but in another
window, now almost hidden in the shadow, stood a fourth and
highly-prized helpmate, which belonged in one sense more to our earth,
since everything examined by it had to be brought near, and lie close
under its magnifying-glass. Yet the MICROSCOPE too could carry its
master into an unseen world, hidden to mortal eye by minuteness instead
of by distance. If in the stillness of night the telescope was his most
cherished servant and familiar friend, the microscope by day opened out
to him the fairyland of nature.
As he sat on his high pedestal stool on this summer night with the
moonlight full upon him, his whole attention was centred on the
telescope, and his mind was far away from that turret-room, wandering
into the distant space brought so near to him; for he was waiting to
watch an event which brought some new interest every time it took
place--a total eclipse of the moon. To-night he looked forward to it
eagerly, for it happened that, just as the moon would pass into the
shadow of our earth, it would also cross directly in front of a star,
causing what is known as an "occultation" of the star, which would
disappear suddenly behind the rim of the dark moon, and after a short
time flash out on the other side as the satellite went on its way.
How he wished as he sat there that he could have shown this sight to all
the eager lads whom he was teaching to handle and love his magic
glasses. For this magician was not only a student himself, he was a rich
man and the Founder and Principal of a large public school for boys of
the artisan class. He had erected a well-planned and handsome building
in the midst of the open country, and received there, on terms within
the means of their parents, working-lads from all parts of England, who,
besides the usual book-learning, received a good technical education in
all its branches. And, while he left to other masters the regular
school lessons, he kept for himself the intense pleasure of opening the
minds of these lads to the wonders of God's universe around them.
You had only to pass down the turret stairs, into the large science
class-room below, to see at once that a loving hand and heart had
furnished it. Not only was there every implement necessary for
scientific work, but numerous rough diagrams covering the walls showed
that labour as well as money had been spent in decorating them. It was a
large oblong room, with four windows to the north, and four to the
south, in each of which stood a microscope with all the tubes, needles,
forceps, knives, etc., necessary for dissecting and preparing objects;
and between the windows were open shelves, on which were ranged
chemicals of various kinds, besides many strange-looking objects in
bottles, which would have amused a trained naturalist, for the lads
collected and preserved whatever took their fancy.
On some of the tables were photographic plates laid ready for printing
off; on others might be seen drawings of the spectrum, made from the
small spectroscope fixed at one end of the room; on others lay small
direct spectroscopes which the lads could use for themselves. But
nowhere was a telescope to be seen. This was not because there were
none, for each table had its small hand-telescope, cheap but good. The
truth is that each of these instruments had been spirited away into the
dormitories that night, and many heads were lying awake on their
pillows, listening for the strike of the clock to spring out and see
the eclipse begin.
[Illustration: Fig. 1.
A boy illustrating the phases of the moon.]
A mere glance round the room showed that the moon had been much studied
lately. On the black-board was drawn a rough diagram, showing how a boy
can illustrate for himself the moon's journey round the earth, by taking
a ball and holding it a little above his head at arm's length, while he
turns slowly round on his heel in a darkened room before a lighted lamp,
or better still before the lens of a magic lantern (Fig. 1). The lamp or
lens then represents the sun, the ball is the moon, the boy's head is
the earth. Beginning with the ball between him and the source of light,
but either a little above, or a little below the direct line between his
eye and it, he will see only the dark side of the ball, and the moon
will be on the point of being "new." Then as he turns slowly, a thin
crescent of light will creep over the side nearest the sun, and by
degrees encroach more and more, so that when he has turned through one
quarter of the round half the disc will be light. When he has turned
another quarter, and has his back to the sun, a full moon will face him.
Then as he turns on through the third quarter a crescent of darkness
creeps slowly over the side away from the sun, and gradually the bright
disc is eaten away by shadow till at the end of the third quarter half
the disc again only is light; then, when he has turned through another
quarter and completed the circle, he faces the light again and has a
dark moon before him. But he must take care to keep the moon a little
above or a little below his eye at new and full moon. If he brings it
exactly on a line with himself and the light at new moon, he will shut
off the light from himself and see the dark body of the ball against the
light, causing an _eclipse_ of the sun; while if he does the same at
full moon his head will cast a shadow on the ball causing an _eclipse_
of the moon.
There were other diagrams showing how and why such eclipses do really
happen at different times in the moon's path round the earth; but
perhaps the most interesting of all was one he had made to explain what
so few people understand, namely, that though the moon describes a
complete circle round our earth every month, yet she does not describe a
circle in space, but a wavy line inwards and outwards across the
earth's path round the sun. This is because the earth is moving on all
the while, carrying the moon with it, and it is only by seeing it drawn
before our eyes that we can realise how it happens.
Thus suppose, in order to make the dates as simple as possible, that
there is a new moon on the 1st of some month. Then by the 9th (or
roughly speaking in 7¾ days) the moon will have described a quarter
of a circle round the earth as shown by the dotted line (Fig. 2), which
marks her position night after night with regard to us. Yet because she
is carried onwards all the while by the earth, she will really have
passed along the interrupted line - - - - between us and the sun. During
the next week her quarter of a circle will carry her round behind the
earth, so that we see her on the 17th as a full moon, yet her actual
movement has been onwards along the interrupted line on the farther side
of the earth. During the third week she creeps round another quarter of
a circle so as to be in advance of the earth on its yearly journey round
the sun, and reaches the end of her third quarter on the 24th. In her
last quarter she gradually passes again between the earth and the sun;
and though, as regards the earth, she appears to be going back round to
the same place where she was at the beginning of the month, and on the
31st is again a dark new moon, yet she has travelled onwards exactly as
much as we have, and therefore has really not described a circle in the
_heavens_ but a wavy line.
[Illustration: Fig. 2.
Diagram showing the moon's course during one month. The moon and the
earth are both moving onwards in the direction of the arrows. The earth
moves along the dark line, the moon along the interrupted line - - - -.
The dotted curved line .... shows the circle gradually described by the
moon round the earth as they move onwards.]
Near to this last diagram hung another, well loved by the lads, for it
was a large map of the _face_ of the moon, that is of the side which is
_always_ turned towards us, because the moon turns once on her axis
during the month that she is travelling round the earth. On this map
were marked all the different craters, mountains, plains and shining
streaks which appear on the moon's face; while round the chart were
pictures of some of these at sunrise and sunset on the moon, or during
the long day of nearly a fortnight which each part of the face enjoys in
its turn.
[Illustration: Fig. 3.
Chart of the moon.
Craters--
1 Tycho. 4 Aristarchus. 7 Plato. 10 Petavius.
2 Copernicus. 5 Eratosthenes. 8 Eudoxus. 11 Ptolemy.
3 Kepler. 6 Archimedes. 9 Aristotle.
Grey plains formerly believed to be seas--
A Mare Crisium. O Mare Imbrium.
C ---- Frigoris. Q Oceanus Procellarum.
G ---- Tranquillitatis. X Mare Foecunditatis.
H ---- Serenitatis. T ---- Humorum.]
By studying this map, and the pictures, they were able, even in their
small telescopes, to recognise Tycho and Copernicus, and the mountains
of the moon, after they had once grown accustomed to the strange
changes in their appearance which take place as daylight or darkness
creeps over them. They could not however pick out more than some of the
chief points. Only the magician himself knew every crater and ridge
under all its varying lights, and now, as he waited for the eclipse to
begin, he turned to a lad who stood behind him, almost hidden in the
dark shadow--the one fortunate boy who had earned the right to share
this night's work.
[Illustration: Fig. 3_a_.
The full moon. (From Ball's _Starland_.)]
"We have still half an hour, Alwyn," said he, "before the eclipse will
begin, and I can show you the moon's face well to-night. Take my place
here and look at her while I point out the chief features. See first,
there are the grey plains (A, C, G, etc.) lying chiefly in the lower
half of the moon. You can often see these on a clear night with the
naked eye, but you must remember that then they appear more in the upper
part, because in the telescope we see the moon's face inverted or upside
down.
"These plains were once thought to be oceans, but are now proved to be
dry flat regions situated at different levels on the moon, and much like
what deserts and prairies would appear on our earth if seen from the
same distance. Looking through the telescope, is it not difficult to
imagine how people could ever have pictured them as a man's face? But
not so difficult to understand how some ancient nations thought the moon
was a kind of mirror, in which our earth was reflected as in a
looking-glass, with its seas and rivers, mountains and valleys; for it
does look something like a distant earth, and as the light upon it is
really reflected from the sun it was very natural to compare it to a
looking-glass.
"Next cast your eye over the hundreds of craters, some large, others
quite small, which cover the moon's face with pitted marks, like a man
with small-pox; while a few of the larger rings look like holes made in
a window-pane, where a stone has passed through, for brilliant shining
streaks radiate from them on all sides like the rays of a star, covering
a large part of the moon. Brightest of all these starred craters is
Tycho, which you will easily find near the top of the moon (I, Fig. 3),
for you have often seen it in the small telescope. How grand it looks
to-night in the full moon (Fig. 3_a_)! It is true you see all the
craters better when the moon is in her quarters, because the light falls
sideways upon them and the shadows are more sharply defined; yet even at
the full the bright ray of light on Tycho's rim marks out the huge
cavity, and you can even see faintly the magnificent terraces which run
round the cup within, one below the other."
[Illustration: Fig. 4.
Tycho and his surroundings. (From a photograph of the moon taken by Mr.
De la Rue, 1863.)]
"This cavity measures fifty-four miles across, so that if it could be
moved down to our earth it would cover by far the largest part of
Devonshire, or that portion from Bideford on the north, to the sea on
the south, and from the borders of Cornwall on the east, to Exeter on
the west, and it is 17,000 feet or nearly three miles in depth. Even in
the brilliant light of the full moon this enormous cup is dark compared
to the bright rim, but it is much better seen in about the middle of the
second quarter, when the rising sun begins to light up one side while
the other is in black night. The drawing on the wall (Fig. 4), which is
taken from an actual photograph of the moon's face, shows Tycho at this
time surrounded by the numerous other craters which cover this part of
the moon. You may recognise him by the gleaming peak in the centre of
the cup, and by his bright rim which is so much more perfect than those
of his companions. The gleaming peak is the top of a steep cone or hill
rising up 6000 feet, or more than a mile from the base of the crater, so
that even the summit is about two miles below the rim.
"There is one very interesting point in Tycho, however, which is seen at
its very best at full moon. Look outside the bright rim and you will see
that from the shadow which surrounds it there spring on all sides those
strange brilliant streaks (see Fig. 3_a_) which I spoke of just now.
There are others quite as bright, or even brighter, round other craters,
Copernicus (Fig. 6), Kepler, and Aristarchus, lower down on the
right-hand side of the moon; but these of Tycho are far the most widely
spread, covering almost all the top of the face.
"What are these streaks? We do not know. During the second quarter of
the moon, when the sun is rising slowly upon Tycho, lighting up his
peak and showing the crater beautifully divided into a bright cup in the
curve to the right, while a dense shadow lies in the left hollow, these
streaks are only faint, and among the many craters around (see Fig. 4)
you might even have some difficulty at first in finding the well-known
giant. But as the sun rises higher and higher they begin to appear, and
go on increasing in brightness till they shine with that wonderfully
silvery light you see now in the full moon."
[Illustration: Fig. 5.
Plan of the Peak of Teneriffe, showing how it resembles a lunar crater.
(A. Geikie.)]
"Here is a problem for you young astronomers to solve, as we learn more
and more how to use the telescope with all its new appliances."
The crater itself is not so difficult to explain, for we have many like
it on our earth, only not nearly so large. In fact, we might almost say
that our earthly volcanoes differ from those in the moon only by their
smaller size and by forming _mountains_ with the crater or cup on the
top; while the lunar craters lie flat on the surface of the moon, the
hollow of the cup forming a depression below it. The peak of Teneriffe
(Fig. 5), which is a dormant volcano, is a good copy in miniature on our
earth of many craters on the moon. The large plain surrounded by a high
rocky wall, broken in places by lava streams, the smaller craters
nestling in the cup, and the high peak or central crater rising up far
above the others, are so like what we see on the moon that we cannot
doubt that the same causes have been at work in both cases, even though
the space enclosed in the rocky wall of Teneriffe measures only eight
miles across, while that of Tycho measures fifty-four.
"But of the streaks we have no satisfactory explanation. They pass alike
over plain and valley and mountain, cutting even across other craters
without swerving from their course. The astronomer Nasmyth thought they
were the remains of cracks made when the volcanoes were active, and
filled with molten lava from below, as water oozes up through ice-cracks
on a pond. But this explanation is not quite satisfactory, for the lava,
forcing its way through, would cool in ridges which ought to cast a
shadow in sunlight. These streaks, however, not only cast no shadow, as
you can see at the full moon but when the sun shines sideways upon them
in the new or waning moon they disappear as we have seen altogether.
Thus the streaks, so brilliant at full moon in Tycho, Copernicus,
Kepler, and Aristarchus, remain a puzzle to astronomers still."
[Illustration: Fig. 6.
The crater Copernicus. (As given in Herschel's _Astronomy_, from a
drawing taken in a reflecting telescope of 20 feet focal length.)]
"We cannot examine these three last-named craters well to-night with the
full sun upon them; but mark their positions well, for Copernicus, at
least, you must examine on the first opportunity, when the sun is
rising upon it in the moon's second quarter. It is larger even than
Tycho, measuring fifty-six miles across, and has a hill in the centre
with many peaks; while outside, great spurs or ridges stretch in all
directions sometimes for more than a hundred miles, and between these
are scattered innumerable minute craters. But the most striking feature
in it is the ring, which is composed inside the crater of magnificent
terraces divided by deep ravines. These terraces are in some ways very
like those of the great crater of Teneriffe, and astronomers can best
account for them by supposing that this immense crater was once filled
with a lake of molten lava rising, cooling at the edges, and then
falling again, leaving the solid ridge behind. The streaks are also
beautifully shown in Copernicus (see Fig. 6), but, as in Tycho, they
fade away as the sun sets on the crater, and only reappear gradually as
midday approaches.
"And now, looking a little to the left of Copernicus, you will see that
grand range of mountains, the Lunar Apennines (Fig. 7), which stretches
400 miles across the face of the moon. Other mountain ranges we could
find, but none so like mountains on our own globe as these, with their
gentle sunny slope down to a plain on the left, and steep perpendicular
cliffs on the right. The highest peak in this range, called Huyghens,
rises to the height of 21,000 feet, higher than Chimborazo in the Andes.
Other mountains on the moon, such as those called the Caucasus, south of
the Apennines, are composed of disconnected peaks, while others again
stand as solitary pyramids upon the plains."
[Illustration: Fig. 7.
The Lunar Apennines.
(Copied by kind permission of MM. Henri from part of a magnificent
photograph taken by them, March 29, 1890, at the Paris Observatory.)]
"But we must hasten on, for I want you to observe those huge walled
crater-plains which have no hill in the middle, but smooth steel-grey
centres shining like mirrors in the moonlight. One of these, called
Archimedes, you will find just below the Lunar Apennines (Figs. 3 and
7), and another called Plato, which is sixty miles broad, is still lower
down the moon's face (Figs. 3 and 8). The centres of these broad
circles are curiously smooth and shining like quicksilver, with minute
dots here and there which are miniature craters, while the walls are
rugged and crowned with turret-shaped peaks."
[Illustration: Fig. 8.
The crater Plato as seen soon after sunrise. (After Neison.)]
"It is easy to picture to oneself how these may once have been vast seas
of lava, not surging as in Copernicus, and heaving up as it cooled into
one great central cone, but seething as molten lead does in a crucible,
little bubbles bursting here and there into minute craters; and this is
the explanation given of them by astronomers.
"And now that you have seen the curious rugged face of the moon and its
craters and mountains, you will want to know how all this has come
about. We can only form theories on the point, except that everything
shows that heat and volcanoes have in some way done the work, though no
one has ever yet clearly proved that volcanic eruptions have taken place
in our time. We must look back to ages long gone by for those mighty
volcanic eruptions which hurled out stones and ashes from the great
crater of Tycho, and formed the vast seas of lava in Copernicus and
Plato.
"And when these were over, and the globe was cooling down rapidly, so
that mountain ranges were formed by the wrinkling and rending of the
surface, was there then any life on the moon? Who can tell? Our magic
glasses can reveal what now is, so far as distance will allow; but what
has been, except where the rugged traces remain, we shall probably never
know. What we now see is a dead worn-out planet, on which we cannot
certainly trace any activity except that of heat in the past. That there
is no life there now, at any rate of the kind on our own earth, we are
almost certain; first, because we can nowhere find traces of water,
clouds, nor even mist, and without moisture no life like ours is
possible; and secondly, because even if there is, as perhaps there may
be, a thin ocean of gas round the moon there is certainly no atmosphere
such as surrounds our globe.
"One fact which proves this is, that there are no half-shadows on the
moon. If you look some night at the mountains and craters during her
first and second quarters, you will be startled to see what heavy
shadows they cast, not with faint edges dying away into light, but sharp
and hard (see Figs. 6-8), so that you pass, as it were by one step, from
shadow to sunshine. This in itself is enough to show that there is no
air to scatter the sunlight and spread it into the edges of the shade as
happens on our earth; but there are other and better proofs. One of
these is, that during an eclipse of the sun there is no reflection of
his light round the dark moon as there would be if the moon had an
atmosphere; another is that the spectroscope, that wonderful instrument
which shows us invisible gases, gives no hint of air around the moon;
and another is the sudden disappearance or _occultation_ of a star
behind the moon, such as I hope to see in a few minutes.
"See here! take the small hand telescope and turn it on to the moon's
face while I take my place at the large one, and I will tell you what to
look for. You know that at sunset we see the sun for some time after it
has dipped below the horizon, because the rays of light which come from
it are bent in our atmosphere and brought to our eyes, forming in them
the image of the sun which is already gone. Now in a short time the moon
which we are watching will be darkened by our earth coming between it
and the sun, and while it is quite dark it will pass over a little
bright star. In fact to us the star will appear to set behind the dark
moon as the sun sets below the horizon, and if the moon had an
atmosphere like ours, the rays from the star would be bent in it and
reach our eyes after the star was gone, so that it would only disappear
gradually. Astronomers have always observed, however, that the star is
lost to sight quite suddenly, showing that there is no ocean of air
round the moon to bend the light-rays."
[Illustration: Fig. 9.
Diagram of total eclipse of the moon.
S, Sun. E, Earth. M, Moon passing into the earth's shadow and passing
out at M´.
R, R´, Lines meeting at a point U, U´ behind the earth and enclosing a
space within which all the direct rays of the sun are intercepted by the
earth, causing a black darkness or _umbra_.
R, P and R´, P´, Lines marking a space within which, behind the earth,
part of the sun's rays are cut off, causing a half-shadow or _penumbra_,
P, P´.
_a_, _a_, Points where a few of the sun's rays are bent or refracted in
the earth's atmosphere, so that they pass along the path marked by the
dotted lines and shed a lurid light on the sun's face.]
Here the magician paused, for a slight dimness on the lower right-hand
side of the moon warned him that she was entering into the _penumbra_ or
half-shadow (see Fig. 9) caused by the earth cutting off part of the
sun's rays; and soon a deep black shadow creeping over Aristarchus and
Plato showed that she was passing into that darker space or _umbra_
where the body of the earth is completely between her and the sun and
cuts off all his rays. All, did I say? No! not all. For now was seen a
beautiful sight, which would prove to any one who saw our earth from a
great distance that it has a deep ocean of air round it.
It was a clear night, with a cloudless sky, and as the deep shadow crept
slowly over the moon's face, covering the Lunar Apennines and
Copernicus, and stealing gradually across the brilliant streaks of Tycho
till the crater itself was swallowed up in darkness, a strange lurid
light began to appear. The part of the moon which was eclipsed was not
wholly dark, but tinted with a very faint bluish-green light, which
changed almost imperceptibly, as the eclipse went on, to rose-red, and
then to a fiery copper-coloured glow as the moon crept entirely into the
shadow and became all dark. The lad watching through his small telescope
noted this weird light, and wondered, as he saw the outlines of the
Apennines and of several craters dimly visible by it, though the moon
was totally eclipsed. He noted, but was silent. He would not disturb the
Principal, for the important moment was at hand, as this dark
copper-coloured moon, now almost invisible, drew near to the star over
which it was to pass.
This little star, really a glorious sun billions of miles away behind
the moon, was perhaps the centre of another system of worlds as unknown
to us as we to them, and the fact of our tiny moon crossing between it
and our earth would matter as little as if a grain of sand was blown
across the heavens. Yet to the watchers it was a great matter--would the
star give any further clue to the question of an atmosphere round the
moon? Would its light linger even for a moment, like the light of the
setting sun? Nearer and nearer came the dark moon; the star shone
brilliantly against its darkness; one second and it was gone. The long
looked-for moment had passed, and the magician turned from his
instrument with a sigh. "I have learnt nothing new, Alwyn," said he,
"but at least it is satisfactory to have seen for ourselves the proof
that there is no perceptible atmosphere round the moon. We need wait no
longer, for before the star reappears on the other side the eclipse will
be passing away."
"But, master," burst forth the lad, now the silence was broken, "tell me
why did that strange light of many tints shine upon the dark moon?"
"Did you notice it, Alwyn?" said the Principal, with a pleased smile.
"Then our evening's work is not lost, for you have made a real
observation for yourself. That light was caused by the few rays of the
sun which grazed the edge of our earth passing through the ocean of air
round it (see Fig. 9). There they were refracted or bent, and so were
thrown within the shadow cast by our earth, and fell upon the moon. If
there were such a person as a 'man in the moon,' that lurid light would
prove to him that our earth has an atmosphere. The cause of the tints is
the same which gives us our sunset colours, because as the different
coloured waves which make white light are absorbed one by one, passing
through the denser atmosphere, the blue are cut off first, then the
green, then the yellow, till only the orange and red rays reached the
centre of the shadow, where the moon was darkest. But this is too
difficult a subject to begin at midnight."
So saying, he lighted his lamp, and covering the object-glass of his
telescope with its pasteboard cap, detached the instrument from the
clockwork, and the master and his pupil went down the turret stairs and
past through the room below. As they did so they heard in the distance a
scuffling noise like that of rats in the wall. A smile passed over the
face of the Principal, for he knew that his young pupils, who had been
making their observations in the gallery above, were hurrying back to
their beds.
CHAPTER II
MAGIC GLASSES, AND HOW TO USE THEM
[Illustration]
The sun shone brightly into the science class-room at mid-day. No gaunt
shadows nor ghostly moonlight now threw a spell on the magic chamber
above. The instruments looked bright and business-like, and the
Principal, moving amongst them, heard the subdued hum of fifty or more
voices rising from below. It was the lecture hour, and the subject for
the day was, "Magic glasses, and how to use them." As the large clock in
the hall sounded twelve, the Principal gathered up a few stray lenses
and prisms he had selected, and passed down the turret stair to his
platform. Behind him were arranged his diagrams, before him on the table
stood various instruments, and the rows of bright faces beyond looked up
with one consent as the hum quieted down and he began his lecture.
"I have often told you, boys, have I not? that I am a Magician. In my
chamber near the sky I work spells as did the magicians of old, and by
the help of my magic glasses I peer into the secrets of nature. Thus I
read the secrets of the distant stars; I catch the light of wandering
comets, and make it reveal its origin; I penetrate into the whirlpools
of the sun; I map out the craters of the moon. Nor can the tiniest being
on earth hide itself from me. Where others see only a drop of muddy
water, that water brought into my magic chamber teems with thousands of
active bodies, darting here and whirling there amid a meadow of tiny
green plants floating in the water. Nay, my inquisitive glass sees even
farther than this, for with it I can watch the eddies of water and green
atoms going on in each of these tiny beings as they feed and grow.
Again, if I want to break into the secrets of the rock at my feet, I
have only to put a thin slice of it under my microscope to trace every
crystal and grain; or, if I wish to learn still more, I subject it to
fiery heat, and through the magic prisms of my spectroscope I read the
history of the very substances of which it is composed. If I wish to
study the treasures of the wide ocean, the slime from a rock-pool teems
with fairy forms darting about in the live box imprisoned in a crystal
home. If some distant stars are invisible even in the giant glasses of
my telescope, I set another power to work, and make them print their own
image on a photographic plate and so reveal their presence.
"All these things you have seen through my magic glasses, and I
promised you that one day I would explain to you how they work and do my
bidding. But I must warn you that you must give all your attention;
there is no royal road to my magician's power. Every one can attain to
it, but only by taking trouble. You must open your eyes and ears, and
use your intelligence to test carefully what your senses show you.
"We have only to consider a little to see that we depend entirely upon
our senses for our knowledge of the outside world. All kinds of things
are going on around us, about which we know nothing, because our eyes
are not keen enough to see, and our ears not sharp enough to hear them.
Most of all we enjoy and study nature through our eyes, those windows
which let in to us the light of heaven, and with it the lovely sights
and scenes of earth; and which are no ordinary windows, but most
wonderful structures adapted for conveying images to the brain. They are
of very different power in different people, so that a long-sighted
person sees a lovely landscape where a short-sighted one sees only a
confused mist; while a short-sighted person can see minute things close
to the eye better than a long-sighted one."
[Illustration: Fig. 10.
Eye-ball seen from the front. (After Le Gros Clark.)
_w_, White of eye. _i_, Iris. _p_, Pupil.]
"Let us try to understand this before we go on to artificial glasses,
for it will help us to explain how these glasses show us many things we
could never see without them. Here are two pictures of the human eyeball
(Figs. 10 and 11), one as it appears from the front, and the other as we
should see the parts if we cut an eyeball across from the front to the
back. From these drawings we see that the eyeball is round; it only
looks oval, because it is seen through the oval slit of the eyelids.
It is really a hard, shining, white ball with a thick nerve cord
(_on_, Fig. 11) passing out at the back, and a dark glassy mound
_c_, _c_ in the centre of the white in front. In this mound we can
easily distinguish two parts--first, the coloured _iris_ or elastic
curtain (_i_, Fig. 10); and secondly, the dark spot or pupil _p_ in the
centre. The iris is the part which gives the eye its colour; it is
composed of a number of fibres, the outer ones radiating towards the
centre, the inner ones forming a ring round the pupil; and behind these
fibres is a coat of dark pigment or colouring matter, blue in some
people, grey, brown, or black in others. When the light is very strong,
and would pain the nerves inside if too much entered the pupil or window
of the eye, then the ring of the iris contracts so as partly to close
the opening. When there is very little light, and it is necessary to let
in as much as possible, the ring expands and the pupil grows large. The
best way to observe this is to look at a cat's eyes in the dusk, and
then bring her near to a bright light; for the iris of a cat's eye
contracts and expands much more than ours does."
[Illustration: Fig. 11.
Section of an eye looking at a pencil. (Adapted from Kirke.)
_c_, _c_, Cornea. _w_, White of eye. _cm_, Ciliary muscle. _a_, _a_,
Aqueous humour. _i_, _i_, Iris. _l_, _l_, Lens. _r_, _r_, Retina. _on_,
Optic nerve. 1, 2, Pencil. 1´, 2´, Image of pencil on the retina.]
"Now look at the second diagram (Fig. 11) and notice the chief points
necessary in seeing. First you will observe that the pupil is not a mere
hole; it is protected by a curved covering _c_. This is the cornea, a
hard, perfectly transparent membrane, looking much like a curved
watch-glass. Behind this is a small chamber filled with a watery fluid
_a_, called the aqueous humour, and near the back of this chamber is the
dark ring or iris _i_, which you saw from the front through the cornea
and fluid. Close behind the iris again is the natural 'magic glass' of
our eye, the crystalline lens _l_, which is composed of perfectly
transparent fibres and has two rounded or convex surfaces like an
ordinary magnifying glass. This lens rests on a cushion of a soft
jelly-like substance _v_, called the vitreous humour, which fills the
dark chamber or cavity of the eyeball and keeps it in shape, so that the
retina _r_, which lines the chamber, is kept at a proper distance from
the lens. This retina is a transparent film of very sensitive nerves; it
forms a screen at the back of the chamber, and has a coating of very
dark pigment or colouring matter behind it. Lastly, the nerves of the
retina all meet in a bundle, called the optic nerve, and passing out of
the eyeball at a point _on_, go to the brain. These are the chief parts
we use in seeing; now how do we use them?
"Suppose that a pencil is held in front of the eye at the distance at
which we see small objects comfortably. Light is reflected from all
parts of the surface of the pencil, and as the rays spread, a certain
number enter the pupil of the eye. We will follow only two cones of
light coming from the points 1 and 2 on the diagram Fig. 11. These you
see enter the eye, each widely spread over the cornea _c_. They are bent
in a little by this curved covering, and by the liquid behind it, while
the iris cuts off the rays near the edges of the lens, which would be
too much bent to form a clear image. The rest of the rays fall upon the
lens _l_. In passing through this lens they are very much bent (or
_refracted_) towards each other, so much so that by the time they reach
the end of the dark chamber _v_, each cone of light has come to a point
or focus 1´, 2´, and as rays of this kind have come from every point all
over the pencil, exactly similar points are formed on the retina, and a
real picture of the pencil is formed there between 1´ and 2´."
[Illustration: Fig. 12.
Image of a candle-flame thrown on paper by a lens.]
"We will make a very simple and pretty experiment to illustrate this.
Darkening the room I light a candle, take a square of white paper in my
hand, and hold a simple magnifying glass between the two (see Fig. 12)
about three inches away from the candle. Then I shift the paper nearer
and farther behind the lens, till we get a clear image of the
candle-flame upon it. This is exactly what happens in our eye. I have
drawn a dotted line _c_ round the lens and the paper on the diagram to
represent the eyeball in which the image of the candle-flame would be on
the retina instead of on the piece of paper. The first point you will
notice is that the candle-flame is upside down on the paper, and if you
turn back to Fig. 11 you will see why, for it is plain that the cones of
light _cross_ in the lens _l_, 1 going to 1´ and 2 to 2´. Every picture
made on our retina is upside down.
"But it is not there that we see it. As soon as the points of light from
the pencil strike upon the retina, the thrill passes on along the optic
nerve _on_, through the back of the eye to the brain; and our mind,
following back the rays exactly as they have come through the lens, sees
a pencil, outside the eye, right way upwards.
"This is how we see with our eyes, which adjust themselves most
beautifully to our needs. For example, not only is the iris always ready
to expand or contract according as we need more or less light, but there
is a special muscle, called the ciliary muscle (_cm_, Fig. 11), which
alters the lens for us to see things far or near. In all, or nearly all,
perfect eyes the lens is flatter in front than behind, and this enables
us to see things far off by bringing the rays from them exactly to a
focus on the retina. But when we look at nearer things the rays require
to be more bent or refracted, so without any conscious effort on our
part this ciliary muscle contracts and allows the lens to bulge out
slightly in front. Instantly we have a stronger magnifier, and the rays
are brought to the right focus on the retina, so that a clear and
full-size image of the near object is formed. How little we think, as we
turn our eyes from one thing to another, and observe, now the distant
hills, now the sheep feeding close by; or, as night draws on, gaze into
limitless space and see the stars millions upon millions of miles away,
that at every moment the focus of our eye is altering, the iris is
contracting or expanding, and myriads of images are being formed one
after the other in that little dark chamber, through which pass all the
scenes of the outer world!
"Yet even this wonderful eye cannot show us everything. Some see farther
than others, some see more minutely than others, according as the lens
of the eye is flatter in one person and more rounded in another. But the
most long-sighted person could never have discovered the planet Neptune,
more than 2700 millions of miles distant from us, nor could the
keenest-sighted have known of the existence of those minute and
beautiful little plants, called diatoms, which live around us wherever
water is found, and form delicate flint skeletons so infinitesimally
small that thousands of millions go to form one cubic inch of the stone
called tripoli, found at Bilin in Bohemia."
[Illustration: Fig. 13.
Arrow magnified by a convex lens.
_a_, _b_, Real arrow. C, D, Magnifying-glass. A, B, Enlarged image of
the arrow.]
"It is here that our 'magic glasses' come to our assistance, and reveal
to us what was before invisible. We learnt just now that we see near
things by the lens of our eye becoming more rounded in front; but there
comes a point beyond which the lens cannot bulge any more, so that when
a thing is very tiny, and would have to be held very close to the eye
for us to see it, the lens can no longer collect the rays to a focus, so
we see nothing but a blur. More than 800 years ago an Arabian, named
Alhazen, explained why rounded or convex glasses make things appear
larger when placed before the eye. This glass which I hold in my hand
is a simple magnifying-glass, such as we used for focusing the
candle-flame. It bends the rays inwards from any small object (see the
arrow _a_, _b_, Fig. 13) so that the lens of our eye can use them, and
then, as we follow out the rays in straight lines to the place where we
see clearly (at A, B), every point of the object is magnified, and we
not only see it much larger, but every mark upon it is much more
distinct. You all know how the little shilling magnifying-glasses you
carry show the most lovely and delicate structures in flowers, on the
wings of butterflies, on the head of a bee or fly, and, in fact, in all
minute living things."
[Illustration: Fig. 14.
Student's microscope. _ep_, Eye-piece. _o_, _g_, Object-glass.]
[Illustration: Fig. 15.
Skeleton of a microscope, showing how an object is magnified.
_o_, _l_, Object-lens. _e_, _g_, Eye-glass. _s_, _s_, Spicule.
_s´_, _s´_, Magnified image of same in the tube. S, S, Image again
enlarged by the lens of the eye-piece.]
"But this is only our first step. Those diatoms we spoke of just now
will only look like minute specks under even the strongest
magnifying-glass. So we pass on to use two extra lenses to assist our
eyes, and come to this compound microscope (Fig. 14) through which I
have before now shown you the delicate markings on shells which were
themselves so minute that you could not see them with the naked eye. Now
we have to discover how the microscope performs this feat. Going back
again for a minute to our candle and magnifying-glass (Fig. 12), you
will find that the nearer you put the lens to the candle the farther
away you will have to put the paper to get a clear image. When in a
microscope we put a powerful lens _o_, _l_ close down to a very minute
object, say a spicule of a flint sponge _s_, _s_, quite invisible to the
unaided eye, the rays from this spicule are brought to a focus a long
way behind it at _s´_, _s´_, making an enlarged image because the lines
of light have been diverging ever since they crossed in the lens. If you
could put a piece of paper at _s´_ _s´_, as you did in the candle
experiment, you would see the actual image of the magnified spicule upon
it. But as these points of light are only in an empty tube, they pass
on, spreading out again from the image, as they did before from the
spicule. Then another convex lens or eye-glass _e_, _g_ is put at the
top of the microscope at the proper distance to bend these rays so that
they enter our eye in nearly parallel lines, exactly as we saw in the
ordinary magnifying-glass (Fig. 13), and our crystalline lens can then
bring them to a focus on our retina.
"By this time the spicule has been twice magnified; or, in other words,
the rays of light coming from it have been twice bent towards each
other, so that when our eye follows them out in straight lines they are
widely spread, and we see every point of light so clearly that all the
spots and markings on this minute spicule are as clear as if it were
really as large as it looks to us.
"This is simply the principle of the microscope. When you come to look
at your own instruments, though they are very ordinary ones, you will
find that the object-glass _o_, _l_ is made of three lenses, flat on the
side nearest the tube, and each lens is composed of two kinds of glass
in order to correct the unequal refraction of the rays, and prevent
fringes of colour appearing at the edge of the lens. Then again the
eye-piece will be a short tube with a lens at each end, and halfway
between them a black ledge will be seen inside the tube which acts like
the iris of our eye (_i_, Fig. 11) and cuts off the rays passing through
the edges of the lens. All these are devices to correct faults in the
microscope which our eye corrects for itself, and they have enabled
opticians to make very powerful lenses.
"Look now at the diagram (Fig. 16) showing a group of diatoms which you
can see under the microscope after the lecture. Notice the lovely
patterns, the delicate tracery, and the fine lines on the diatoms shown
there. Yet each of these minute flint skeletons, if laid on a piece of
glass by itself, would be quite invisible to the naked eye, while
hundreds of them together only look like a faint mist on the slide on
which they lie. Nor are they even here shown as much magnified as they
might be; under a stronger power we should see those delicate lines on
the diatoms broken up into minute round cups."
[Illustration: Fig. 16.
Fossil diatoms seen under the microscope. The largest of these is an
almost imperceptible speck to the naked eye.]
"Is it not wonderful and delightful to think that we are able to add in
this way to the power of our eyes, till it seems as if there were no
limit to the hidden beauties of the minute forms of our earth, if only
we can discover them?
"But our globe does not stand alone in the universe, and we want not
only to learn all about everything we find upon it, but also to look out
into the vast space around us and discover as much as we can about the
myriads of suns and planets, comets and meteorites, star-mists and
nebulæ, which are to be found there. Even with the naked eye we can
admire the grand planet Saturn, which is more than 800 millions of miles
away, and this in itself is very marvellous. Who would have thought that
our tiny crystalline lens would be able to catch and focus rays, sent
all this enormous distance, so as actually to make a picture on our
retina of a planet, which, like the moon, is only sending back to us the
light of the sun? For, remember, the rays which come to us from Saturn
must have travelled twice 800 millions of miles--884 millions from the
sun to the planet, and less or more from the planet back to us,
according to our position at the time. But this is as nothing when
compared to the enormous distances over which light travels from the
stars to us. Even the nearest star we know of, is at least twenty
_millions_ of _millions_ of miles away, and the light from it, though
travelling at the rate of 186,300 miles in a second, takes four years
and four months to reach us, while the light from others, which we can
see without a telescope, is between twenty and thirty years on its road.
Does not the thought fill us with awe, that our little eye should be
able to span such vast distances?
"But we are not yet nearly at the end of our wonder, for the same power
which devised our eye gave us also the mind capable of inventing an
instrument which increases the strength of that eye till we can actually
see stars so far off that their light takes _two thousand years_ coming
to our globe. If the microscope delights us in helping us to see things
invisible without it, because they are so small, surely the telescope is
fascinating beyond all other magic glasses when we think that it brings
heavenly bodies, thousands of billions of miles away, so close to us
that we can examine them."
[Illustration: Fig. 17.
An astronomical telescope.
_ep_, Eye-piece. _og_, Object-glass. _f_, Finder.]
"A Telescope (Fig. 17) can, like the microscope, be made of only two
glasses: an object-glass to form an image in the tube and a magnifying
eye-piece to enlarge it. But there is this difference, that the object
lens of a microscope is put close down to a minute object, so that the
rays fall upon it at a wide angle, and the image formed in the tube is
very much larger than the object outside. In the telescope, on the
contrary, the thing we look at is far off, so that the rays fall on the
object-glass at such a very narrow angle as to be practically parallel,
and the image in the tube is of course _very, very_ much smaller than
the house, or church, or planet it pictures. What the object-glass of
the telescope does for us, is to bring a small _real image_ of an object
very far off close to us in the tube of the telescope so that we can
examine it.
"Think for a moment what this means. Imagine that star we spoke of (p.
41), whose light, travelling 186,300 miles in one second, still takes
2000 years to reach us. Picture the tiny waves of light crossing the
countless billions of miles of space during those two thousand years,
and reaching us so widely spread out that the few faint rays which
strike our eye are quite useless, and for us that star has no existence;
we cannot see it. Then go and ask the giant telescope, by turning the
object-glass in the direction where that star lies in infinite space.
The widespread rays are collected and come to a minute bright image in
the dark tube. You put the eye-piece to this image, and there, under
your eye, is a shining point: this is the image of the star, which
otherwise would be lost to you in the mighty distance.
"Can any magic tale be more marvellous, or any thought grander, or more
sublime than this? From my little chamber, by making use of the laws of
light, which are the same wherever we turn, we can penetrate into depths
so vast that we are not able even to measure them, and bring back unseen
stars to tell us the secrets of the mighty universe. As far as the stars
are concerned, whether we see them or not depends entirely upon the
number of rays collected by the object-glass; for at such enormous
distances the rays have no angle that we can measure, and magnify as
you will, the brightest star only remains a point of light. It is in
order to collect enough rays that astronomers have tried to have larger
and larger object-glasses; so that while a small good hand telescope,
such as you use, may have an object-glass measuring only an inch and a
quarter across, some of the giant telescopes have lenses of two and a
half feet, or thirty inches, diameter. These enormous lenses are very
difficult to make and manage, and have many faults, therefore
astronomical telescopes are often made with curved mirrors to _reflect_
the rays, and bring them to a focus instead of _refracting_ them as
curved lenses do.
"We see, then, that one very important use of the telescope is to bring
objects into view which otherwise we would never see; for, as I have
already said, though we bring the stars into sight, we cannot magnify
them. But whenever an object is near enough for the rays to fall even at
a very small perceptible angle on the object-glass, then we can magnify
them; and the longer the telescope, and the stronger the eye-piece, the
more the object is magnified.
[Illustration: Fig. 18.
Skeletons of telescopes.
A, A one-foot telescope with a three-inch eye-piece. B, A two-foot
telescope with a three-inch eye-piece. _e_, _p_, Eye-piece. _o_, _g_,
Object-glass. _r_, _r_, Rays which enter the telescopes and crossing at
_x_ form an image at _i_, _i_, which is magnified by the lens _e_, _p_.
The angles _r_, _x_, _r_ and _i_, _x_, _i_ are the same. In A the angle
_i_, _o_, _i_ is four times greater than that of _i_, _x_, _i_. In B it
is eight times greater.]
"I want you to understand the meaning of this, for it is really very
simple, only it requires a little thought. Here are skeleton drawings of
two telescopes (Fig. 18), one double the length of the other. Let us
suppose that two people are using them to look at an arrow on a
weathercock a long distance off. The rays of light _r_, _r_ from the
two ends of the arrow will enter both telescopes at the same angle
_r_, _x_, _r_, cross in the lens, and pass on at _exactly the same
angle_ into the tubes. So far all is alike, but now comes the
difference. In the short telescope A the object-glass must be of such a
curve as to bring the cones of light in each ray to a focus at a
distance of _one foot_ behind it,[1] and there a small image _i_, _i_ of
the arrow is formed. But B being twice the length, allows the lens
to be less curved, and the image to be formed _two feet_ behind the
object-glass; and as the rays _r_, _r_ have been _diverging_ ever since
they crossed at _x_, the real image of the arrow formed at _i_, _i_ is
twice the size of the same image in A. Nevertheless, if you could put a
piece of paper at _i_, _i_ in both telescopes, and look through the
_object-glass_ (which you cannot actually do, because your head would
block out the rays), the arrow would appear the same size in both
telescopes, because one would be twice as far off from you as the other,
and the angle _i_, _x_, _i_ is the same in both."
[1] In our Fig. 18 the distances are inches instead of feet, but the
proportions are the same.
"But by going to the proper end of the telescope you can get quite near
the image, and can see and magnify it, if you put a strong lens to
collect the rays from it to a focus. This is the use of the eye-piece,
which in our diagram is placed at a quarter of a foot or three inches
from the image in both telescopes. Now that we are close to the images,
the divergence of the points _i_, _i_ makes a great difference. In the
small telescope, in which the image is only _one foot_ behind the
object-glass, the eye-piece being a quarter of a foot from it, is four
times nearer, so the angle _i_, _o_, _i_ is four times the angle
_i_, _x_, _i_, and the man looking through it sees the image magnified
_four times_. But in the longer telescope the image is _two feet_ behind
the lens, while the eye-piece is, as before, a quarter of a foot from
it. Thus the eyepiece is now eight times nearer, so the angle
_i_, _o_, _i_ is eight times the angle _i_, _x_, _i_, and the observer
sees the image magnified _eight times_.
"In real telescopes, where the difference between the focal length of
the object-glass and that of the eye-glass can be made enormously
greater, the magnifying power is quite startling, only the object-glass
must be large, so as to collect enough rays to bear spreading widely.
Even in your small telescopes, with a focus of eighteen inches, and an
object-glass measuring one and a quarter inch across, we can put on a
quarter of an inch eye-piece, and so magnify seventy-two times; while in
my observatory telescope, eight feet or ninety-six inches long, an
eye-piece of half an inch magnifies 192 times, and I can put on a
1/8-inch eye-piece and magnify 768 times! And so we can go on
lengthening the focus of the object-glass and shortening the focus of
the eye-piece, till in Lord Rosse's gigantic fifty-six-foot telescope,
in which the image is fifty-four feet (648 inches) behind the
object-glass, an eye-piece one-eighth of an inch from the image
magnifies 5184 times! These giant telescopes, however, require an
enormous object-glass or mirror, for the points of light are so spread
out in making the large image that it is very faint unless an enormous
number of rays are collected. Lord Rosse's telescope has a reflecting
mirror measuring six feet across, and a man can walk upright in the
telescope tube. The most powerful telescope yet made is that at the Lick
Observatory, on Mount Hamilton, in California. It is fifty-six and a
half feet long, the object-lens measures thirty-six inches across. A
star seen through this telescope appears 2000 times as bright as when
seen with the naked eye.
"You need not, however, wait for an opportunity to look through giant
telescopes, for my small student's telescope, only four feet long, which
we carry out on to the lawn, will show you endless unseen wonders; while
your hand telescopes, and even a common opera-glass, will show many
features on the face of the moon, and enable you to see the crescent of
Venus, Jupiter's moons, and Saturn's rings, besides hundreds of stars
unseen by the naked eye.
"Of course you will understand that Fig. 18 only shows the _principle_
of the telescope. In all good instruments the lenses and other parts are
more complicated; and in a terrestrial telescope, for looking at
objects on the earth, another lens has to be put in to turn them right
way up again. In looking at the sky it does not matter which way up we
see a planet or a star, so the second glass is not needed, and we lose
light by using it.
"We have now three magic glasses to work for us--the magnifying-glass,
the microscope, and the telescope. Besides these, however, we have two
other helpers, if possible even more wonderful. These are the
Photographic camera and the Spectroscope."
[Illustration: Fig. 19.
Photographic camera.
_l_, _l_, Lenses. _s_, _s_, Screen cutting off diverging rays. _c_, _c_,
Sliding box. _p_, _p_, Picture formed.]
"Now that we thoroughly understand the use of lenses, I need scarcely
explain this photographic camera (Fig. 19), for it is clearly an
artificial eye. In place of the _crystalline lens_ (compare with Fig.
11) the photographer uses one, or generally two lenses _l_, _l_, with a
black ledge or stop _s_ between them, which acts like the iris in
cutting off the rays too near the edge of the lens. The dark camera _c_
answers to the _dark chamber_ of the eyeball, and the plate _p_, _p_ at
the back of the chamber, which is made sensitive by chemicals, answers
our _retina_. The box is formed of two parts, sliding one within the
other at _c_, so as to place the plate at a proper distance from the
lens, and then a screw adjusts the focus more exactly by bringing the
front lens back or forward, instead of altering the curve as the
_ciliary muscle_ does in our eye. The difference between the two
instruments is that in our eye the message goes to the brain, and the
image disappears when we turn our eyes away from the object; but in the
camera the waves of light work upon the chemicals, and the image can be
fixed and remain for ever.
"But the camera has at least one weak point. The screen at the back is
not curved like our retina, but must be flat because of printing off the
pictures, and therefore the parts of the photograph near the edge are a
little out of proportion.
"In many ways, however, this photographic eye is a more faithful
observer than our own, and helps us to make more accurate pictures. For
instance, instantaneous photographs have been taken of a galloping
horse, and we find that the movements are very different from what we
thought we saw with our eye, because our retina does not throw off one
impression after another quickly enough to be quite certain we see each
curve truly in succession. Again, the photograph of a face gives minute
curves and lines, lights and shadows, far more perfectly than even the
best artist can see them, and when the picture is magnified we see more
and more details which escaped us before.
"But it is especially when attached to the microscope or the telescope
that the photographic apparatus tells us such marvellous secrets;
giving us, for instance, an accurate picture of the most minute
water-animal quite invisible to the naked eye, so that when we enlarge
the photograph any one can see the beautiful markings, the finest fibre,
or the tiniest granule; or affording us accurate pictures, such as the
one at p. 19 of the face of the moon, and bringing stars into view which
we cannot otherwise see even with the strongest telescope.
"Our own eye has many weaknesses. For example, when we look through the
telescope at the sky we can only fix our attention on one part at once,
and afterwards on another; and the picture which we see in this way, bit
by bit, we must draw as best we can. But if we put a sensitive
photographic plate into the telescope just at the point (_i_, _i_, Fig.
18), where the _image_ of the sky is focused, this plate gives
attention, so to speak, to the whole picture at once, and registers
every point exactly as it is; and this picture can be kept and enlarged
so that every detail can be seen.
"Then, again, if we look at faint stars, they do not grow any brighter
as we look. Each ray sends its message to the brain, and that is all; we
cannot heap them up in our eye, and, indeed, after a time we see less,
because our nerves grow tired. But on a photographic plate in a
telescope, each ray in its turn does a little work upon the chemicals,
and the longer the plate remains, the stronger the picture becomes. When
wet plates were used they could not be left long, but since dry plates
have been invented, with a film of chemically prepared gelatine, they
can be left for hours in the telescope, which is kept by clockwork
accurately opposite to the same objects. In this way thousands of faint
stars, which we cannot see with the strongest telescope, creep into view
as their feeble rays work over and over again on the same spot; and, as
the brighter stars as well as the faint ones are all the time making
their impression stronger, when the plate comes out each one appears in
its proper strength. On the other hand, very bright objects often become
blurred by a long exposure, so that we have sometimes to sacrifice the
clearness of a bright object in order to print faint objects clearly.
"We now come to our last magic glass--the Spectroscope; and the hour has
slipped by so fast that I have very little time left to speak of it. But
this matters less as we have studied it before.[1] I need now only
remind you of some of the facts. You will remember that when we passed
sunlight through a three-sided piece of glass called a prism, we broke
up a ray of white light into a line of beautiful colours gradually
passing from red, through orange, yellow, green, blue, and indigo, to
violet, and that these follow in the same order as we see them in the
rainbow or in the thin film of a soap-bubble. By various experiments we
proved that these colours are separated from each other because the many
waves which make up white light are of different sizes, so that because
the waves, of red light are slow and heavy, they lag behind when bent in
the three-sided glass, while the rapid violet waves are bent more out of
their road and run to the farther end of the line, the other colours
ranging themselves between."
[1] _Fairyland of Science_, Lecture II.; and _Short History of Natural
Science_, chapter xxxiv.
"Now when the light falls through the open window, or through a round
hole or _large_ slit, the images of the hole made by each coloured wave
overlap each other very much, and the colours in the spectrum or
coloured band are crowded together. But when in the spectroscope we pass
the ray of light through a very narrow slit, each coloured image of the
upright slit overlaps the next upright image only very little. By using
several prisms one after the other (see Fig. 21), these upright coloured
lines are separated more and more till we get a very long band or
spectrum. Yet, as you know from our experiments with the light of a
glowing wire or of molten iron, however much you spread out the light
given by a solid or liquid, you can never separate these coloured lines
from each other. It is only when you throw the light of a glowing gas or
vapour into the slit that you get a few bright lines standing out alone.
This is because _all_ the rays of white light are present in glowing
solids and liquids, and they follow each other too closely to be
separated. But a gas, such as glowing hydrogen for example, gives out
only a few separate rays, which, pouring through the slit, throw red,
greenish-blue, and dark blue lines on the screen. Thus you have seen the
double, orange-yellow sodium line (3, Plate I.) which starts out at once
when salt is held in a flame and its light thrown into the spectroscope,
and the red line of potassium vapour under the same treatment; and we
shall observe these again when we study the coloured lights of the sun
and stars."
[Illustration: Fig. 20.
Kirchhoff's spectroscope.
A, The telescope which receives the ray of light through the slit in O.]
[Illustration: Fig. 21.
Passage of rays through the spectroscope.
S, S´, Slit through which the light falls on the prisms. 1, 2, 3, 4,
Prisms in which the rays are dispersed more and more. _a_, _b_, Screen
receiving the spectrum, of which the seven principal colours are
marked.]
"We see, then, that the work of our magic glass, the spectroscope, is
simply to sift the waves of light, and that these waves, from their
colour and their position in the long spectrum, actually tell us what
glowing gases have started them on their road. Is not this like magic?
I take a substance made of I know not what; I break it up, and, melting
it in the intense heat of an electric spark, throw its light into the
spectroscope. Then, as I examine this light after it has been spread out
by the prisms, I can actually read by unmistakable lines what metals or
non-metals it contains. Nay, more; when I catch the light of a star, or
even of a faint nebula, in my telescope, and pass it through these
prisms, there, written up on the magic-coloured band, I read off the
gases which are glowing in that star-sun or star-dust billions of miles
away.
"Now, boys, I have let you into the secrets of my five magic
glasses--the magnifying-glass, the microscope, the telescope, the
photographic camera, and the spectroscope. With these and the help of
chemistry you can learn to work all my spells. You can peep into the
mysteries of the life of the tiniest being which moves unseen under your
feet; you can peer into that vast universe, which we can never visit so
long as our bodies hold us down to our little earth; you can make the
unseen stars print their spots of light on the paper you hold in your
hand, by means of light-waves, which left them hundreds of years ago; or
you can sift this light in your spectroscope, and make it tell you what
substances were glowing in that star when they were started on their
road. All this you can do on one condition, namely, that you seek
patiently to know the truth.
"Stories of days long gone by tell us of true magicians and false
magicians, and the good or evil they wrought. Of these I know nothing,
but I do know this, that the value of the spells you can work with my
magic glasses depends entirely upon whether you work patiently,
accurately, and honestly. If you make careless, inaccurate experiments,
and draw hasty conclusions, you will only do bad work, which it may take
others years to undo; but if you question your instruments honestly and
carefully, they will answer truly and faithfully. You may make many
mistakes, but one experiment will correct the other; and while you are
storing up in your own mind knowledge which lifts you far above this
little world, or enables you to look deep below the outward surface of
life, you may add your little group of facts to the general store, and
help to pave the way to such grand discoveries as those of Newton in
astronomy, Bunsen and Kirchhoff in spectrum analysis, and Darwin in the
world of life."
CHAPTER III
FAIRY RINGS AND HOW THEY ARE MADE
[Illustration]
It was a lovely warm day in September, the golden corn had been cut and
carted, and the waggons of the farmers around were free for the use of
the college lads in their yearly autumn holiday. There they stood in a
long row, one behind the other in the drive round the grounds, each with
a pair of sleek, powerful farm-horses, and the waggoners beside them
with their long whips ornamented with coloured ribbons; and as each
waggon drew up before the door, it filled rapidly with its merry load
and went on its way.
They had a long drive of seven miles before them, for they were going to
cross the wild moor, and then descend gradually along a fairly good road
to the more wooded and fertile country. Their object that day was to
reach a certain fairy dell known to a few only among the party as one of
the loveliest spots in Devon. It was a perfect day for a picnic. As they
drove over the wide stretches of moorland, with tors to right and tors
to the left, the stunted furze bushes growing here and there glistened
with spiders' webs from which the dew had not yet disappeared, and
mosses in great variety carpeted the ground, from the lovely
thread-mosses, with their scarlet caps, to the pale sphagnum of the
bogs, where a halt was made for some of the botanists of the party to
search for the little Sundew (_Drosera rotundifolia_). Though this
little plant had now almost ceased to flower, it was not difficult to
recognise by its rosette of leaves glistening with sticky glands which
it spreads out in many of the Dartmoor bogs to catch the tiny flies and
suck out their life's blood, and several specimens were uprooted and
carefully packed away to plant in moist moss at home.
From this bog onwards the road ran near by one of the lovely streams
which feed the rivers below, and, passing across a bridge covered with
ivy, led through a small forest of stunted trees round which the
woodbine clung, hanging down its crimson berries, and the bracken fern,
already putting on its brown and yellow tints, grew tall and thick on
either side. Then, as they passed out of the wood, they came upon the
dell, a piece of wild moorland lying in a hollow between two granite
ridges, with large blocks of granite strewn over it here and there, and
furze bushes growing under their shelter, still covered with yellow
blossoms together with countless seed-bearing pods, which the
youngsters soon gathered for the shiny-black seeds within them.
Here the waggons were unspanned, the horses tethered out, the food
unpacked, and preparations for the picnic soon in full swing. Just at
this moment, however, a loud shout from one part of the dell called
every one's attention. "The fairy rings! the fairy rings! we have found
the fairy rings!" and there truly on the brown sward might be seen three
delicate green rings, the fresh sprouting grass growing young and tender
in perfect circles measuring from six feet to nearly three yards across.
"What are they?" The question came from many voices at once, but it was
the Principal who answered.
"Why, do you not know that they are pixie circles, where the 'elves of
hills, brooks, standing lakes, and groves' hold their revels, whirling
in giddy round, and making the rings, 'whereof the ewe not bites'? Have
you forgotten how Mrs. Quickly, in the _Merry Wives of Windsor_, tells
us that
"'nightly, meadow-fairies, look you sing,
Like to the Garter's compass, in a ring:
The expressure that it bears, green let it be,
More fertile-fresh than all the field to see'?
"If we are magicians and work spells under magic glasses, why should not
the pixies work spells on the grass? I brought you here to-day on
purpose to see them. Which of you now can name the pixie who makes
them?"
A deep silence followed. If any knew or guessed the truth of the matter,
they were too shy to risk making a mistake.
"Be off with you then," said the Principal, "and keep well away from
these rings all day, that you may not disturb the spell. But come back
to me before we return at night, and perhaps I may show you the
wonder-working pixie, and we may take him home to examine under the
microscope."
The day passed as such happy days do, and the glorious harvest moon had
risen over the distant tors before the horses were spanned and the
waggons ready. But the Principal was not at the starting place, and
looking round they saw him at the farther end of the dell.
"Gently, gently," he cried, as there was one general rush towards him;
"look where you tread, for I stand within a ring of fairies!"
And then they saw that just outside the green circle in which he stood,
forming here and there a broken ring, were patches of a beautiful tiny
mushroom, each of which raised its pale brown umbrella in the bright
moonlight.
"Here are our fairies, boys. I am going to take a few home where they
can be spared from the ring, and to-morrow we will learn their history."
* * * * *
The following day saw the class-room full, and from the benches eager
eyes were turned to the eight windows, in each of which stood one of the
elder boys at his microscope ready for work. For under those microscopes
the Principal always arranged some object referred to in his lecture and
figured in diagrams on the walls, and it was the duty of each boy, after
the lecture was over, to show and explain to the class all the points
of the specimen under his care. These boys were always specially envied,
for though the others could, it is true, follow all the descriptions
from the diagrams, yet these had the plant or animal always under their
eye. Discussion was at this moment running high, for there was a great
uncertainty of opinion as to whether a mushroom could be really called a
plant when it had no leaves or flowers. All at once the hush came, as
the Principal stepped into his desk and began:--
"Life is hard work, boys, and there is no being in this world which has
not to work for its living. You all know that a plant grows by taking in
gases and water, and working them up into sap and living tissue by the
help of the sunshine and the green matter in their leaves; and you know,
too, that the world is so full of green plants that hundreds and
thousands of young seedlings can never get a living, but are stifled in
their babyhood or destroyed before they can grow up.
"Now there are many dark, dank places in the world where plants cannot
get enough sunlight and air to make green colouring matter and
manufacture their own food. And so it comes to pass that a certain class
of plants have found another way of living, by taking their food ready
made from other decaying plants and animals, and so avoiding the
necessity of manufacturing it for themselves. These plants can live
hidden away in dark cellars and damp cupboards, in drains and pipes
where no light ever enters, under a thick covering of dead leaves in the
forest, under fallen trunks and mossy stones; in fact, wherever
decaying matter, whether of plant or animal, can be found for them to
feed upon.
"It is to this class, called _fungi_, which includes all mushrooms and
moulds, mildews, smuts, and ferments, that the mushroom belongs which we
found yesterday making the fairy rings. And, in truth, we were not so
far wrong when we called them pixies or imps, for many of them are
indeed imps of mischief, which play sorry pranks in our stores at home
and in the fields and forest abroad. They grow on our damp bread, or
cheese, or pickles; they destroy fruit and corn, hop and vine, and even
take the life of insects and other animals. Yet, on the other hand, they
are useful in clearing out unhealthy nooks and corners, and purifying
the air; and they can be made to do good work by those who know how to
use them; for without ferments we could have neither wine, beer, nor
vinegar, nor even the yeast which lightens our bread.
"I am going to-day to introduce you to this large vagabond class of
plants, that we may see how they live, grow, and spread, what good and
bad work they do, and how they do it. And before we come to the
mushrooms, which you know so well, we must look at the smaller forms,
which do all their work above ground, so that we can observe them. For
the _fungi_ are to be found almost everywhere. The film growing over
manure-heaps, the yeast plant, the wine fungus, and the vinegar plant;
the moulds and mildews covering our cellar-walls and cupboards, or
growing on decayed leaves and wood, on stale fruit, bread, or jam, or
making black spots on the leaves of the rose, the hop, or the vine; the
potato fungus, eating into the potato in the dark ground and producing
disease; the smut filling the grains of wheat and oats with disease, the
ergot feeding on the rye, the rust which destroys beetroot, the rank
toadstools and puffballs, the mushroom we eat, and the truffles which
form even their fruit underground,--all these are _fungi_, or lowly
plants which have given up making their own food in the sunlight, and
take it ready made from the dung, the decaying mould, the root, the
leaf, the fruit, or the germ on which they grow. Lastly, the diseases
which kill the silkworm and the common house-fly, and even some of the
worst skin diseases in man, are caused by minute plants of this class
feeding upon their hosts."
[Illustration: Fig. 22.
Three forms of vegetable mould magnified.
1, _Mucor Mucedo_. 2, _Aspergillus glaucus_. 3, _Penicillium glaucum_.]
"In fact, the _fungi_ are so widely spread over all things living and
dead, that there is scarcely anything free from them in one shape or
another. The minute spores, now of one kind, now of another, float in
the air, and settling down wherever they find suitable food, have
nothing more to do than to feed, fatten, and increase, which they do
with wonderful rapidity. Let us take as an example one of the moulds
which covers damp leaves, and even the paste and jam in our cupboard. I
have some here growing upon a basin of paste, and you see it forms a
kind of dense white fur all over the surface, with here and there a
bluish-green tinge upon it. This white fur is the common mould, _Mucor
Mucedo_ (1, Fig. 22), and the green mould happens in this case to be
another mould, _Penicillium glaucum_ (3, Fig. 22); but I must warn you
that these minute moulds look very much alike until you examine them
under the microscope, and though they are called white, blue, or green
moulds, yet any one of them may be coloured at different times of its
growth. Another very common and beautiful mould, _Aspergillus glaucus_
(2, Fig. 22), often grows with Mucor on the top of jam.
"All these plants begin with a spore or minute colourless cell of living
matter (_s_, Fig. 23), which spends its energy in sending out tubes in
all directions into the leaves, fruit, or paste on which it feeds. The
living matter, flowing now this way now that, lays down the walls of its
tubes as it flows, and by and by, here and there, a tube, instead of
working into the paste, grows upwards into the air and swells at the tip
into a colourless ball in which a number of minute seed-like bodies
called spores are formed. The ball bursts, the spores fall out, and each
one begins to form fresh tubes, and so little by little the mould grows
denser and thicker by new plants starting in all directions.
"Under the first microscope you will see a slide showing the tubes which
spread through the paste, and which are called the _mycelium_ (_m_, Fig.
23), and amongst it are three upright tubes, one just starting _a_,
another with the fruit ball forming _b_, and a third _c_, which is
bursting and throwing out the spores. The _Aspergillus_ and the
_Penicillium_ differ from the _Mucor_ in having their spores naked and
not enclosed in a spore-case. In _Penicillium_ they grow like the beads
of a necklace one above the other on the top of the upright tube, and
can very easily be separated (see Fig. 22); while _Aspergillus_, a most
lovely silvery mould, is more complicated in the growth of its spores,
for it bears them on many rows branching out from the top of the tube
like the rays of a star."
[Illustration: Fig. 23.
_Mucor Mucedo_, greatly magnified. (After Sachs and Brefeld.)
_m_, Mycelium, or tangle of threads. _a_, _b_, _c_, Upright tubes in
different stages. _c_, Spore-case bursting and sending out spores. _s_,
1, 2, 3, A growing spore, in different stages, starting a new mycelium.]
"I want you to look at each of these moulds carefully under the
microscope, for few people who hastily scrape a mould away, vexed to
find it on food or damp clothing, have any idea what a delicate and
beautiful structure lies under their hand. These moulds live on decaying
matter, but many of the mildews, rusts, and other kinds of fungus, prey
upon living plants such as the _smut_ of oats (_Ustilago carbo_), and
the _bunt_ (_Tilletia caria_) which eats away the inside of the grains
of wheat, while another fungus attacks its leaves. There is scarcely a
tree or herb which has not one fungus to prey upon it, and many have
several, as, for example, the common lime-tree, which is infested by
seventy-four different fungi, and the oak by no less than 200.
"So these colourless food-taking plants prey upon their neighbours,
while they take their oxygen for breathing from air. The 'ferments,'
however, which live _inside_ plants or fluids, take even their oxygen
for breathing from their hosts.
"If you go into the garden in summer and pluck an overripe gooseberry,
which is bursting like this one I have here, you will probably find that
the pulp looks unhealthy and rotten near the split, and the gooseberry
will taste tart and disagreeable. This is because a small fungus has
grown inside, and worked a change in the juice of the fruit. At first
this fungus spread its tubes outside and merely _fed_ upon the fruit,
using oxygen from the air in breathing; but by and by the skin gave way,
and the fungus crept inside the gooseberry where it could no longer get
any fresh air. In this dilemma it was forced to break up the sugar in
the fruit and take the oxygen out of it, leaving behind only alcohol and
carbonic acid which give the fermented taste to the fruit.
"So the fungus-imp feeds and grows in nature, and when man gets hold of
it he forces it to do the same work for a useful purpose, for the
grape-fungus grows in the vats in which grapes are crushed and kept away
from air, and tearing up the sugar, leaves alcohol behind in the
grape-juice, which in this way becomes wine. So, too, the yeast-fungus
grows in the malt and hop liquor, turning it into beer; its spores
floating in the fluid and increasing at a marvellous rate, as any
housewife knows who, getting yeast for her bread, tries to keep it in a
corked bottle.
"The yeast plant has never been found wild. It is only known as a
cultivated plant, growing on prepared liquor. The brewer has to sow it
by taking some yeast from other beer, or by leaving the liquor exposed
to air in which yeast spores are floating; or it will sow itself in the
same way in a mixture of water, hops, sugar, and salt, to which a
handful of flour is added. It increases at a marvellous rate, one cell
budding out of another, while from time to time the living matter in a
cell will break up into four parts instead of two, and so four new cells
will start and bud. A drop of yeast will very soon cover a glass slide
with this tiny plant, as you will see under the second microscope, where
they are now at work (Fig. 24)."
[Illustration: Fig. 24.
Yeast cells growing under the microscope. _a_, Single cells. _b_, Two
cells forming by division. _c_, A group of cells where division is going
on in all directions.]
"But perhaps the most curious of all the minute fungi are those which
grow inside insects and destroy them. At this time of year you may
often see a dead fly sticking to the window-pane with a cloudy white
ring round it; this poor fly has been killed by a little fungus called
_Empusa muscæ_. A spore from a former plant has fallen perhaps on the
window-pane, or some other spot over which the fly has crawled, and
being sticky has fixed itself under the fly's body. Once settled on a
favourable spot it sends out a tube, and piercing the skin of the fly,
begins to grow rapidly inside. There it forms little round cells one
after the other, something like the yeast-cells, till it fills the whole
body, feeding on its juices; then each cell sends a tube, like the
upright tubes of the _Mucor_ (Fig. 23) out again through the fly's skin,
and this tube bursts at the end, and so new spores are set free. It is
these tubes, and the spores thrown from them, which you see forming a
kind of halo round the dead fly as it clings to the pane. Other fungi in
the same way kill the silkworm and the caterpillars of the cabbage
butterfly. Nor is it only the lower animals which suffer. When we once
realise that fungus spores are floating everywhere in the air, we can
understand how the terrible microscopic fungi called _bacteria_ will
settle on an open wound and cause it to fester if it is not properly
dressed.
"Thus we see that these minute fungi are almost everywhere. The larger
ones, on the contrary, are confined to the fields and forests, damp
walls and hollow trees; or wherever rotting wood, leaves, or manure
provide them with sufficient nourishment. Few people have any clear
ideas about the growth of a mushroom, except that the part we pick
springs up in a single night. The real fact is, that a whole mushroom
plant is nothing more than a gigantic mould or mildew, only that it is
formed of many different shaped cells, and spreads its tubes
_underground_ or through the trunks of trees instead of in paste or jam,
as in the case of the mould."
[Illustration: Fig. 25.
Early stages of the mushroom. (After Sachs.)
_m_, Mycelium. _b1-3_, Mushroom buds of different ages. _b4_, Button
mushroom. _g_, Gills forming inside before lower attachment of the cap
gives way at _v_.]
"The part which we gather and call a mushroom, a toadstool, or a
puffball is only the fruit, answering to the round balls of the mould.
The rest of the plant is a thick network of tubes, which you will see
under the third microscope. These tubes spread underground and suck in
decayed matter from the earth; they form the _mycelium_ (_m_, Fig. 25)
such as we found in the mould. The mushroom-growers call it 'mushroom
spawn' because they use it to spread over the ground for new crops. Out
of these underground tubes there springs up from time to time a swollen
round body no bigger at first than a mustard seed (_b1_, Fig. 25). As it
increases in size it comes above ground and grows into the mushroom or
spore-case, answering to the round balls which contain the spores of the
mould. At first this swollen body is egg-shaped, the top half being
largest and broadest, and the fruit is then called a 'button-mushroom'
_b4_. Inside this ball are now formed a series of folds made of long
cells, some of which are soon to bear spores just as the tubes in the
mould did, and while these are forming and ripening, a way out is
preparing for them. For as the mushroom grows, the skin of the lower
part of the ball (_v_, _b4_) is stretched more and more, till it can
bear the strain no longer and breaks away from the stalk; then the ball
expands into an umbrella, leaving a piece of torn skin, called the veil
(_v_, Fig. 26), clinging to the stalk."
[Illustration: Fig. 26.
Later stages of the mushroom. (After Gautier.)
1, Button mushroom stage. _c_, Cap. _v_, Veil. _g_, Gills.
2, Full-grown mushroom, showing veil v after the cap is quite free, and
the gills or lamellæ _g_, of which the structure is shown in Fig. 27.]
"All this happens in a single night, and the mushroom is complete, with
a stem up the centre and a broad cap, under which are the folds which
bear the spores. Thus much you can see for yourselves at any time by
finding a place where mushrooms grow and looking for them late at night
and early in the morning so as to get the different stages. But now we
must turn to the microscope, and cutting off one of the folds, which
branch out under the cap like the spokes of a wheel, take a slice across
it (1, Fig. 27) and examine."
[Illustration: Fig. 27.
1, One of the gills or lamellæ of the mushroom slightly magnified,
showing the cells round the edge. _c_, Cells which do not bear spores.
_fc_, Fertile cells. 2, A piece of the edge of the same powerfully
magnified, showing how the spores _s_ grow out of the tip of the fertile
cells _fc_.]
"First, under a moderate power, you will see the cells forming the
centre of the fold and the layer of long cells (_c_ and _fc_) which are
closely packed all round the edge. Some of these cells project beyond
the others, and it is they which bear the spores. We see this plainly
under a very strong power when you can distinguish the sterile cells _c_
and the fertile cells _fc_ projecting beyond them, and each bearing
four spore-cells _s_ on four little horns at its tip.
"These spores fall off very easily, and you can make a pretty experiment
by cutting off a large mushroom head in the early morning and putting it
flat upon a piece of paper. In a few hours, if you lift it very
carefully, you will find a number of dark lines on the paper, radiating
from a centre like the spokes of a wheel, each line being composed of
the spores which have fallen from a fold as it grew ripe. They are so
minute that many thousands would be required to make up the size of the
head of an ordinary pin, yet if you gather the spores of the several
kinds of mushroom, and examine them under a strong microscope, you will
find that even these specks of matter assume different shapes in the
various species.
"You will be astonished too at the immense number of spores contained in
a single mushroom head, for they are reckoned by millions; and when we
remember that each one of these is the starting point of a new plant, it
reminds us forcibly of the wholesale destruction of spores and seeds
which must go on in nature, otherwise the mushrooms and their companions
would soon cover every inch of the whole world.
"As it is, they are spread abroad by the wind, and wherever they escape
destruction they lie waiting in every nook and corner till, after the
hot summer, showers of rain hasten the decay of plants and leaves, and
then the mushrooms, toadstools, and puffballs, grow at an astounding
pace. If you go into the woods at this season you may see the enormous
deep-red liver fungus (_Fistulina hepatica_) growing on the oak-trees,
in patches which weigh from twenty to thirty pounds; or the glorious
orange-coloured fungus (_Tremella mesenterica_) growing on bare sticks
or stumps of furze; or among dead leaves you may easily chance on the
little caps of the crimson, scarlet, snowy white, or orange-coloured
fungi which grow in almost every wood. From white to yellow, yellow to
red, red to crimson and purple black, there is hardly any colour you may
not find among this gaily-decked tribe; and who can wonder that the
small bright-coloured caps have been supposed to cover tiny imps or
elves, who used the large mushrooms to serve for their stools and
tables?
"There they work, thrusting their tubes into twigs and dead branches,
rotting trunks and decaying leaves, breaking up the hard wood and tough
fibres, and building them up into delicate cells, which by and by die
and leave their remains as food for the early growing plants in the
spring. So we see that in their way the mushrooms and toadstools are
good imps after all, for the tender shoot of a young seedling plant
could take no food out of a hard tree-trunk, but it finds the work done
for it by the fungus, the rich nourishment being spread around its young
roots ready to be imbibed.
"To find our fairy-ring mushrooms, however, we must leave the wood and
go out into the open country, especially on the downs and moors and
rough meadows, where the land is poor and the grass coarse and spare.
There grow the nourishing kinds, most of which we can eat, and among
these is the delicate little champignon or 'Scotch-bonnet' mushroom,
_Marasmius Oreades_,[1] which makes the fairy-rings. When a spore of
this mushroom begins to grow, it sucks up vegetable food out of the
earth and spreads its tubes underground, in all directions from the
centre, so that the mycelium forms a round patch like a thick
underground circular cobweb. In the summer and autumn, when the weather
is suitable, it sends up its delicate pale-brown caps, which we may
gather and eat without stopping the growth of the plant.
[1] Shown in initial letter of this chapter.
"This goes on year after year underground, new tubes always travelling
outwards till the circle widens and widens like the rings of water on a
pond, only that it spreads very slowly, making a new ring each year,
which is often composed of a mass of tubes as much as a foot thick in
the ground, and the tender tubes in the centre die away as the new ones
form a larger hoop outside.
"But all this is below ground; where then are our fairy rings? Here is
the secret. The tubes, as we have seen, take up food from the earth and
build it up into delicate cells, which decay very soon, and as they die
make a rich manure at the roots of the grass. So each season the cells
of last year's ring make a rich feeding-ground for the young grass,
which springs up fresh and green in a fairy ring, while _outside_ this
emerald circle the mushroom tubes are still growing and increasing
underneath the grass, so that next year, when the present ring is no
longer richly fed, and has become faded and brown like the rest of the
moor, another ring will spring up outside it, feeding on the prepared
food below."
"In bad seasons, though the tubes go on spreading and growing below, the
mushroom fruit does not always appear above ground. The plant will only
fruit freely when the ground has been well warmed by the summer sun,
followed by damp weather to moisten it. This gives us a rich crop of
mushrooms all over the country, and it is then you can best see the ring
of fairy mushrooms circling outside the green hoop of fresh grass. In
any case the early morning is the time to find them; it is only in very
sheltered spots that they sometimes last through the day, or come up
towards evening, as I found them last night on the warm damp side of the
dell.
"This is the true history of fairy rings, and now go and look for
yourselves under the microscopes. Under the first three you will find
the three different kinds of mould of our diagram (Fig. 22). Under the
fourth the spores of the mould are shown in their first growth putting
out the tubes to form the mycelium. The fifth shows the mould itself
with its fruit-bearing tubes, one of which is bursting. Under the sixth
the yeast plant is growing; the seventh shows a slice of one of the
folds of the common mushroom with its spore-bearing horns; and under the
eighth I have put some spores from different mushrooms, that you may see
what curious shapes they assume.
"Lastly, let me remind you, now that the autumn and winter are coming,
that you will find mushrooms, toadstools, puffballs, and moulds in
plenty wherever you go. Learn to know them, their different shapes and
colours, and above all the special nooks each one chooses for its home.
Look around in the fields and woods and take note of the decaying plants
and trees, leaves and bark, insects and dead remains of all kinds. Upon
each of these you will find some fungus growing, breaking up their
tissues and devouring the nourishing food they provide. Watch these
spots, and note the soft spongy soil which will collect there, and then
when the spring comes, notice what tender plants flourish upon these
rich feeding grounds. You will thus see for yourselves that the fungi,
though they feed upon others, are not entirely mischief-workers, but
also perform their part in the general work of life."
CHAPTER IV
THE LIFE-HISTORY OF LICHENS AND MOSSES
[Illustration]
The autumn has passed away and we are in the midst of winter. In the
long winter evenings the stars shine bright and clear, and tempt us to
work with the telescope and its helpmates the spectroscope and
photographic plates. But at first sight it would seem as though our
microscopes would have to stand idle so far at least as plants are
concerned, or be used only to examine dried specimens and mounted
sections. Yet this is not the fact, as I remembered last week when
walking through the bare and leafless wood. A startled pheasant rising
with a whirr at the sound of my footsteps among the dead leaves roused
me from my thoughts, and as a young rabbit scudded across the path and I
watched it disappear among the bushes, I was suddenly struck with the
great mass of plant life flourishing underfoot and overhead.
Can you guess what plants these were? I do not mean the evergreen pines
and firs, nor the few hardy ferns, nor the lovely ivy clothing the
trunks of the trees. Such plants as these live and remain green in the
winter, but they do not grow. If you wish to find plant life revelling
in the cold damp days of winter, fearing neither frost nor snow and
welcoming mist and rain, you must go to the mosses, which as autumn
passes away begin to cover the wood-paths, to creep over the roots of
the trees, to suck up the water in the bogs, and even to clothe dead
walls and stones with a soft green carpet. And with the mosses come the
lichens, those curious grey and greenish oddities which no one but a
botanist would think of classing among plants.
The wood is full of them now: the hairy lichens hang from the branches
of many of the trees, making them look like old greybearded men; the
leafy lichens encircle the branches, their pale gray, green, and yellow
patches looking as if they were made of crumpled paper cut into wavy
plates; and the crusty lichens, scarcely distinguishable from the bark
of the trees, cover every available space which the mosses have left
free.
As I looked at these lichens and thought of their curious history I
determined that we would study them to-day, and gathered a basketful of
specimens (see Fig. 28). But when I had collected these I found I had
not the heart to leave the mosses behind. I could not even break off a
piece of bark with lichen upon it without some little moss coming too,
especially the small thread-mosses (_Bryum_) which make a home for
themselves in every nook and corner of the branches; while the
feather-mosses, hair-mosses, cord-mosses, and many others made such a
lovely carpet under my feet that each seemed too beautiful to pass by,
and they found their way into my basket, crowned at the top with a large
mass of the pale-green Sphagnum, or bog-moss, into which I sank more
than ankle-deep as I crossed the bog in the centre of the wood on my way
home.
[Illustration: Fig. 28.
Examples of Lichens. (From life.)
1, A hairy lichen. 2, A leafy lichen. 3, A crustaceous lichen. _f_, _f_,
the fruit.]
So here they all are, and I hope by the help of our magic glass to let
you into some of the secrets of their lives. It is true we must study
the structure of lichens chiefly by diagrams, for it is too minute for
beginners to follow under the microscope, so we must trust to drawings
made by men more skilful in microscopic botany, at any rate for the
present. But the mosses we can examine for ourselves and admire their
delicate leaves and wonderful tiny spore-cases.
Now the first question which I hope you want to ask is, how it is that
these lowly plants flourish so well in the depth of winter when their
larger and stronger companions die down to the ground. We will answer
this first as to the lichens, which are such strange uncanny-looking
plants that it is almost difficult to imagine they are alive at all; and
indeed they have been a great puzzle to botanists.
[Illustration: Fig. 29.
Single-celled green plants growing and dividing (_Pleurococcus_). (After
Thuret and Bornet.)]
Before we examine them, however, look for a minute at a small drop of
this greenish film which I have taken from the rain-water taken outside.
I have put some under each microscope, and those who can look into them
will see the slide almost covered with small round green cells very much
like the yeast cells we saw when studying the Fungi, only that instead
of being colourless they are a bright green. Some of these cells will I
suspect be longer than others, and these long cells will be moving over
the slide very rapidly, swimming hither and thither, and you will see,
perhaps for the first time, that very low plants can swim about in
water. These green cells are, indeed, the simplest of all plants, and
are merely bags of living matter which, by the help of the green
granules in them, are able to work up water and gases into nourishing
food, and so to live, grow, and multiply.
There are many kinds of these single-celled plants in the world. You may
find them on damp paths, in almost any rain-water butt, in ponds and
ditches, in sparkling waterfalls, along the banks of flowing rivers, and
in the cold clear springs on the bleak mountains. Some of them take the
form of tangled threads[1] composed of long strings of cells, and these
sometimes form long streamers in flowing water, and at other times are
gathered together in a shapeless film only to be disentangled under a
microscope. Other kinds[2] wave to and fro on the water, forming dense
patches of violet, orange-brown, or glossy green scum shining in the
bright sunlight, and these flourish equally in the ponds of our gardens
and in pools in the Himalaya mountains, 18,000 feet above the sea.
Others again[3] seize on every damp patch on tree trunks, rocks, or
moist walls, covering them with a green powder formed of single plant
cells. Other species of this family turn a bright red colour when the
cells are still; and one, under the name of Gory Dew,[4] has often
frightened the peasants of Italy, by growing very rapidly over damp
walls and then turning the colour of blood. Another[5] forms the "red
snow" of the Arctic regions, where it covers wide surfaces of snow with
a deep red colour. Others[6] form a shiny jelly over rocks and stones,
and these may be found almost everywhere, from the garden path to the
warm springs of India, from the marshes of New Zealand up to the shores
of the Arctic ocean, and even on the surface of floating icebergs.
[1] _Confervæ._
[2] _Oscillariæ._
[3] _Protococcus._
[4] _Palmella cruenta._
[5] _Protococcus nivalis._
[6] _Nostoc._
The reason why these plants can live in such very different regions is
that they do not take their food through roots out of the ground, but
suck in water and gases through the thin membrane which covers their
cell, and each cell does its own work. So it matters very little to them
where they lie, so long as they have moisture and sunlight to help them
in their work. Wherever they are, if they have these, they can take in
carbonic acid from the air and work up the carbon with other gases which
they imbibe with the water, and so make living material. In this way
they grow, and as a cell grows larger the covering is stretched and part
of the digested food goes to build up more covering membrane, and by and
by the cell divides into two and each membrane closes up, so that there
are two single-celled plants where there was only one before. This will
sometimes go on so fast that a small pond may be covered in a few hours
with a green film formed of new cells.
Now we have seen, when studying mushrooms, that the one difference
between these green plants and the single-celled Fungi is that while the
green cells make their own food, colourless cells can only take it in
ready-made, and therefore prey upon all kinds of living matter. This is
just what happens in the lichens; and botanists have discovered that
these curious growths are really the result of a _partnership_ between
single-celled green plants and single-celled fungi. The grey part is a
fungus; but when it is examined under the microscope we find it is not a
fungus only; a number of green cells can be seen scattered through it,
which, when carefully studied, prove to be some species of the green
single-celled plants.
Here are two drawings of sections cut through two different lichens, and
enormously magnified so that the cells are clearly seen. 1, Fig. 30 is
part of a hairy lichen (1, Fig. 28), and 2 is part of a leafy lichen (2,
Fig. 28). The hairy lichen as you see has a row of green cells all round
the tiny branch, with fungus cells on all sides of them. The leafy
lichen, which only presents one surface to the sun and air while the
other side is against the tree, has only one layer of green cells near
the surface, but protected by the fungus above.
[Illustration: Fig. 30.
Sections of Lichens. (Sachs.)
1, Section of a hairy lichen, _Usnea barbata_. 2, Section of a leafy
lichen, _Sticta fuliginosa_. 3, Early growth of a lichen. _gc_, Green
cells. _f_, Fungus.]
The way the lichen has grown is this. A green cell (_gc_ 3, Fig. 30)
falling on some damp spot has begun to grow and spread, working up food
in the sunlight. To it comes the spore of the fungus _f_, first
thrusting its tubes into the tree-bark, or wall, and then spreading
round the green cells, which remain always in such a position that
sunlight, air, and moisture can reach them. From this time the two
classes of plants live as friends, the fungus using part of the food
made by the green cells, and giving them in return the advantage of
being spread out to the sunlight, while they are also protected in
frosty or sultry weather when they would dry up on a bare surface. On
the whole, however, the fungus probably gains the most, for it has been
found, as we should expect, that the green cells can live and grow if
separated out of the lichen, but the fungus cells die when their
industrious companions are taken from them.
At any rate the partnership succeeds, as you will see if you go into the
wood, or into an orchard where the apple-trees are neglected, for every
inch of the branches is covered by lichens if not already taken up by
mosses or toadstools.
There is hardly any part of the world except the tropics where lichens
do not abound. In the Alps of Scandinavia close to the limits of
perpetual snow, in the sandy wastes of Arctic America, and over the
dreary Tundras of Arctic Siberia, where the ground is frozen hard during
the greater part of the year, they flourish where nothing else can live.
The little green cells multiply by dividing, as we saw them doing in the
green film from the water-butt. The fungus, however, has many different
modes of seeding itself. One of these is by forming little pockets in
the lichen, out of which, when they burst, small round bodies are
thrown, which cover the lichen with a minute green powder. There is
plenty of this powder on the leafy lichen which you have by you. You can
see it with the magnifying-glass, without putting it under the
microscope. As long as the lichen is dry these round bodies do not grow,
but as soon as moisture reaches them they start away and become new
plants.
[Illustration: Fig. 31.
Fructification of a lichen. (From Sachs and Oliver.)
Apothecium or spore-chamber of a lichen. 1, Closed. 2, Open. 3, The
spore-cases and filaments enlarged, showing the spores. _f_, Filaments.
_sc_, Spore-cases. _s_, Spores.]
A more complicated and beautiful process is shown in this diagram (Fig.
31). If you look carefully at the leafy lichen (2, Fig. 28) you will
find here and there some little cups _f_, while others grow upon the
tips of the hairy lichen. These cups, or fruits, were once closed,
flask-shaped chambers (1, Fig. 31) inside which are formed a number of
oval cells _sc_, which are spore-cases, with from four to eight spores
or seed-like bodies _s3_ inside them. When these chambers, which are
called _apothecia_, are ripe, moist or rainy weather causes them to
swell at the top, and they burst open and the spore-cases throw out the
spores to grow into new fungi.
In some lichens the chambers remain closed and the spores escape through
a hole in the top, and they are then called _perithecia_, while in
others, as these which we have here, they open out into a cup-shape.
This, then, is the curious history of lichens; the green cells and fungi
flourishing together in the damp winter and bearing the hardest frost
far better than the summer drought, so that they have their good time
when most other plants are dead or asleep. Yet though some of them, such
as the hairy lichens, almost disappear in the summer, they are by no
means dead, for, like all these very low plants, they can bear being
dried up for a long time, and then, when moisture visits them again,
each green cell sets to work, and they revive. There is much more to be
learnt about them, but this will be sufficient to make you feel an
interest in their simple lives, and when you look for them in the wood
you will be surprised to find how many different kinds there are, for it
is most wonderful that such lowly plants should build up such an immense
variety of curious and grotesque forms.
* * * * *
And yet, when we turn to the mosses, I am half afraid they will soon
attract you away from the dull grey lichens, for of all plant histories
it appears to me that the history of the moss-plant is most fascinating.
As this history is complicated by the moss having, as it were, two
lives, you must give me your whole attention, and I will explain it
first from diagrams, though you can see all the steps under the
microscope.
Take in your hands, in the first place, a piece of this green moss which
I have brought. How thick it is, like a rich felted carpet! and yet, if
you pull it apart carefully, you will find that each leafy stem is
separate, and can be taken away from the others without breaking
anything. In this dense moss each stem is single and clothed with leaves
wrapped closely round it (see Fig. 33); in some mosses the stem is
branched, and in others the leaves grow on side stalks, as in this
feathery moss (Fig. 32). But in each case every stem is like a separate
plant, with its own tuft of tender roots _r_.
[Illustration: Fig. 32.
A stem of feathery moss. (From life.)
_l_, Leaves. _s_, Stem. _r_, Roots.]
What a delicate growth it is! The stem is scarcely more than a fine
thread, the leaves minute, transparent, and tender. In this pale
sphagnum or bog-moss (Fig. 36, p. 93), which is much larger and stouter,
you can see better how each one of these leaves, though they are so
thickly packed, is placed so that it can get the utmost light, air, and
moisture. Yet so closely are the leaves of each stem entangled in those
of the next that the whole forms a thick springy green carpet under our
feet.
How is it, then, that these moss stems, though each independent, grow in
such a dense mass? Partly because moss multiplies so rapidly that new
stems are always thrusting themselves up to the light, but chiefly
because the stems were not always separate, but in very early life
sprang from a common source.
If, instead of bringing the moss home and tearing it apart, you went to
a spot in the wood where fresh moss was growing, and looked very
carefully on the surface of the ground or among the water of a marsh,
you would find a spongy green mass below the growing moss, very much
like the green scum on a pond. This film, some of which I have brought
home, is seen under the microscope to be a mass of tangled green threads
(_t_, Fig. 34, p. 88) like those of the _Confervæ_ (see p. 79), composed
of rows of cells, while here and there upon these threads you would find
a bud (_mb_, Fig. 34) rising up into the air.
This tangled mass of green threads, called the _protonema_, is the first
growth, from which the moss stems spring. It has itself originated from
a moss-spore; as we shall see by and by. As soon as it has started it
grows and spreads very rapidly, drinking in water and air through all
its cells and sending up the moss buds which swell and grow, giving out
roots below and fine stems above, which soon become crowded with leaves,
forming the velvety carpet we call moss. Meanwhile the soft threads
below die away, giving up all their nourishment to the moss-stems, and
this is why, when you take up the moss, you find each stem separate. But
now comes the question, How does each stem live after the nourishing
threads below have died? It is true each stem has a few hairy roots,
but these are very feeble, and not at all like the roots of higher
plants. The fact is, the moss is built up entirely of tender cells, like
the green cells in the lichen, or in the film upon the pond. These cells
are not shut in behind a thick skin as in the leaves of higher plants,
but have every one of them the power to take in water and gases through
their tender membrane.
I made last night a rough drawing of the leaf of the feathery moss put
under the microscope, but you will see it far better by putting a leaf
with a little water on a glass slide under the covering glass and
examining it for yourself. You will see that it is composed of a number
of oval-shaped cells packed closely together (_c_ Fig. 33), with a few
long narrow ones _mr_ in the middle of the leaf forming the midrib.
Every cell is as clear and distinct as if it were floating in the water,
and the tiny green grains which help it to work up its food are clearly
visible.
[Illustration: Fig. 33.
Moss-leaf magnified. (From life.)
Showing the cells _c_, each of which can take in and work up its own
food. _mr_, Long cells of the mid-rib.]
Each of these cells can act as a separate plant, drinking in the water
and air it needs, and feeding and growing quite independently of the
roots below. Yet at the same time the moss stem has a great advantage
over single-celled plants in having root-hairs, and being able to grow
upright and expose its leaves to the sun and air.
Now you will no longer wonder that moss grows so fast and so thick, and
another curious fact follows from the independence of each cell, namely,
that new growths can start from almost any part of the plant. For
example, pieces will often break off from the tangled mass or protonema
below, and, starting on their own account, form other thread masses.
Then, after the moss stems have grown, a new mass of threads may grow
from one of the tiny root-hairs of a stem and make a fresh tangle; nay,
a thread will sometimes even spring out of a damp moss leaf and make a
new beginning, while the moss stems themselves often put forth buds and
branches, which grow root-hairs and settle down on their own account.
[Illustration: Fig. 34.
Polytrichum commune. A large hair-moss.
_t_, _t_, Threads of green cells forming the _protonema_ out of which
moss-buds spring. _mb_, Buds of moss-stems. _a_, Minute green flower in
which the antherozoids are formed (enlarged in Fig. 35). _p_, _p1_,
_p2_, _p3_, Minute green flower in which the ovules are formed, and
urn-plant springing out of it (enlarged in Fig. 35). _us_, Urn stems.
_c_, Cap. _u_, Urn after cap has fallen off, still protected by its
lid.]
All this comes from the simple nature of the plants, each cell doing its
own work. Nor are the mosses in any difficulty as to soil, for as the
matted threads decay they form a rich manure, and the dying moss-stems
themselves, being so fragile, turn back very readily into food. This is
why mosses can spread over the poorest soil where even tough grasses
cannot live, and clothe walls and roofs with a rich green.
[Illustration: Fig. 35.
Fructification of a moss.
A, Male moss-flower stripped of its outer leaves, showing jointed
filaments and oval sacs os and antherozoid cells _zc_ swarming out of a
sac. _zc´_, Antherozoid cell enlarged. _z_, Free antherozoid. P, Female
flower with bottle-shaped sacs _bs_. _bs-c_, Bottle-shaped sac, with cap
being pushed up. _u_, Urn of _Funaria hygrometrica_, with small cap.
_u´_, Urn, from which the cap has fallen, showing the teeth _t_ which
keep in the spores.]
So far, then, we now understand the growth of the mossy-leaf stems, but
this is only half the life of the plant. After the moss has gone on
through the damp winter spreading and growing, there appear in the
spring or summer tiny moss flowers at the tip of some of the stems.
These flowers (_a_, _p_, Fig. 34) are formed merely of a few green
leaves shorter and stouter than the rest, enclosing some oval sacs
surrounded by jointed hairs or filaments (see A and P, Fig. 35). These
sacs are of two different kinds, one set being short and stout _os_, the
others having long necks like bottles _bs_. Sometimes these two kinds of
sac are in one flower, but more often they are in separate flowers, as
in the hair-moss, _Polytrichum commune_ (_a_ and _p_, Fig. 34). Now when
the flowers are ripe the short sacs in the flower A open and fling out
myriads of cells _zc_, and these cells burst, and forth come tiny
wriggling bodies _z_, called by botanists _antherozoids_, one out of
each cell. These find their way along the damp moss to the flower P, and
entering the neck of one of the bottle-shaped sacs _bs_, find out each
another cell or _ovule_ inside. The two cells together then form a
_plant-egg_, which answers to the germ in the seeds of higher plants.
Now let us be sure we understand where we are in the life of the plant.
We have had its green-growing time, its flowering, and the formation of
what we may roughly call its seed, which last in ordinary higher plants
would fall down and grow into a new green plant. But with the moss there
is more to come. The egg does not shake out of the bottle-necked sac,
but begins to grow inside it, sending down a little tube into the moss
stem, and using it as other plants use the ground to grow in.
As soon as it is rooted it begins to form a delicate stem, and as this
grows it pushes up the sac _bs_, stretching the neck tighter and tighter
till at last it tears away below, and the sac is carried up and hangs
like an extinguisher or cap (_c_ Figs. 34, 35) over the top of the stem.
Meanwhile, under this cap the top of the stalk swells into a knob
which, by degrees, becomes a lovely little covered urn _u_, something
like a poppy head, which has within it a number of spores. The growth of
this tiny urn-plant often occupies several months, for you must remember
that it is not merely a fruit, though it is often called so, but a real
plant, taking in food through its tubes below and working for its
living.
When it is finished it is a most lovely little object (_us_, Fig. 34),
the fine hairlike stalk being covered with a green, yellow, or brilliant
red fool's cap on the top, yet the whole in most mosses is not bigger
than an ordinary pin. You may easily see them in the spring or summer,
or even sometimes in the winter. I have only been able to bring you one
very little one to-day, the _Funaria hygrometrica_, which fruits early
in the year. This moss has only a short cap, but in many mosses they are
very conspicuous. I have often pulled them off as you would pull a cap
from a boy's head. In nature they fall off after a time, leaving the
urn, which, though so small, is a most complicated structure. First it
has an outer skin, with holes or mouths in it which open and close to
let moisture in and out. Then come two layers of cells, then an open
space full of air, in which are the green chlorophyll grains which are
working up food for the tiny plant as the moisture comes in to them.
Lastly, within this again is a mass of tissue, round which grow the
spores which are soon to be sown, and which in _Polytrichum commune_ are
protected by a lid. Even after the extinguisher and the lid have both
fallen off, the spores cannot fall out, for a thick row of teeth (_t_,
Fig. 35) is closed over them like the tentacles of an anemone. So long
as the air is damp these teeth remain closed; it is only in fine dry
weather that they open and the spores are scattered on the ground.
_Funaria hygrometrica_ has no lid under its cap, and after the cap falls
the spores are only protected by the teeth.
When the spores are gone, the life of the tiny urn-plant is over. It
shrivels and dies, leaving ten, fifteen, or even more spores, which,
after lying for some time on the ground, sprout and grow into a fresh
mass of soft threads.
So now we have completed the life-history of the moss and come back to
the point at which we started. I am afraid it has been rather a
difficult history to follow step by step, and yet it is perfectly clear
when once we master the succession of growths. Starting from a spore,
the thread-mass or protonema gives rise to the moss-stems forming the
dense green carpet, then the green flowers on some of the leaf-stems
give rise to a plant-egg, which roots itself in the stem, and grows into
a perfect plant without leaves, bearing merely the urn in which fresh
spores are formed, and so the round goes on from year to year.
There are a great number of different varieties of moss, and they differ
in the shape and arrangement of their stems and leaves, and very much in
the formation of their urns, yet this sketch will enable you to study
them with understanding, and when you find in the wood the nodding caps
of the fruiting plants, some red, some green, some yellow, and some a
brilliant orange, you will feel that they are acquaintances, and by the
help of the microscope may soon become friends.
Among them one of the most interesting is the sphagnum or bog-moss (Fig.
36), which spreads its thick carpet over all the bogs in the woods. You
cannot miss its little orange-coloured spore-cases if you look closely,
for they contrast strongly with its pale green leaves, out of which they
stand on very short stalks. I wish we could examine it, for it differs
much from other mosses, both in leaves and fruit, but it would take us
too long. At least, however, you must put one of its lovely transparent
leaves under the microscope, that you may see the large air-cells which
lie between the growing cells, and admire the lovely glistening bands
which run across and across their covering membrane, for the sphagnum
leaf is so extremely beautiful that you will never forget it when once
seen. It is through these large cells in the edge of the stem and leaf
that the water rises up from the swamp, so that the whole moss is like a
wet sponge.
[Illustration: Fig. 36.
Sphagnum moss from a Devonshire bog. (From life.)]
And now, before we part, we had better sum up the history of lichens and
mosses. With the lichens we have seen that the secret of success seems
to be mutual help. The green cells provide the food, the fungus cells
form a surface over which the green cells can spread to find sunlight
and moisture, and protection from extremes of heat or cold. With the
mosses the secret lies in their standing on the borderland between two
classes of plant life. On the one hand, they are still tender-celled
plants, each cell being able to live its own life and make its own food;
on the other hand, they have risen into shapely plants with the
beginnings of feeble roots, and having stems along which their leaves
are arranged so that they are spread to the light and air. Both lichens
and mosses keep one great advantage common to all tender-celled plants;
they can be dried up so that you would think them dead, and yet, because
they can work all over their surface whenever heat and moisture reach
them, each cell drinks in food again and the plant revives. So when a
scorching sun, or a dry season, or a biting frost kills other plants,
the mosses and lichens bide their time till moisture comes again.
In our own country they grow almost everywhere--on walls, on broken
ground, on sand-heaps, on roofs and walls, on trees living and dead, and
over all pastures which are allowed to grow poor and worn out. They
grow, too, in all damp, marshy spots; especially the bog-mosses forming
the peat-bogs which cover a large part of Ireland and many regions in
Scotland; and these same bog-mosses occur in America, New Zealand, and
Australia.
In the tropics mosses are less abundant, probably because other plants
flourish so luxuriantly; but in Arctic Siberia and Arctic America both
lichens and mosses live on the vast Tundras. There, during the three
short months of summer, when the surface of the ground is soft, the
lichens spread far and wide where all else is lifeless, while in moister
parts the Polytrichums or hair-mosses cover the ground, and in swampy
regions stunted Sphagnums form peat-bogs only a few inches in depth over
the frozen soil beneath. If, then, the lichens and mosses can flourish
even in such dreary latitudes as these, we can understand how they defy
even our coldest winters, appearing fresh and green when the snow melts
away from over them, and leave their cells bathed in water, so that
these lowly plants clothe the wood with their beauty when otherwise all
would be bare and lifeless.
CHAPTER V
THE HISTORY OF A LAVA STREAM
[Illustration]
It is now just twenty-two years ago, boys, since I saw a wonderful
sight, which is still so fresh in my mind that I have to look round and
remember that it was before any of you were born, in order to persuade
myself that it can be nearly a quarter of a century since I stood with
my feet close to a flowing stream of red-hot lava.
It happened in this way. I was spending the winter with friends in
Naples, and we were walking quietly one lovely afternoon in November
along the Villa Reale, the public garden on the sea-shore, when one of
our party exclaimed, "Look at Vesuvius!" We did so, and saw in the
bright sunlight a dense dark cloud rising up out of the cone. The
mountain had been sending out puffs of smoke, with a booming noise, for
several days, but we thought nothing of that, for it had been common
enough for slight eruptions to take place at intervals ever since the
great eruption of 1867. This cloud, however, was far larger and
wider-spread than usual, and as we were looking at it we saw a thin red
line begin some way down the side of the mountain and creep onwards
toward the valley which lies behind the Hermitage near where the
Observatory is built (see Fig. 37). "A crater has broken out on the
slope," said our host; "it will be a grand sight to-night. Shall we go
up and see it?" No sooner proposed than settled, and one of the party
started off at once to secure horses and men before others engaged them.
[Illustration: Fig. 37.
Somma. Vesuvius.
Vesuvius, as seen in eruption by the author, November 1868.]
It was about eight o'clock in the evening when we started in a carriage
for Resina, and alighting there, with buried Herculaneum under our feet,
mounted our horses and set forward with the guides. Then followed a long
ascent of about two hours and a half through the dark night. Silently
and carefully we travelled on over the broad masses of slaggy lava of
former years, along which a narrow horse-path had been worn; and ever
and anon we heard the distant booming in the crater at the summit, and
caught sight of fresh gleams of light as we took some turning which
brought the glowing peak into view.
Our object was to get as close as possible to the newly-opened crater in
the mountain-side, and when we arrived on a small rugged plain not far
from the spot, we alighted from our horses, which were growing
frightened with the glare, and walked some distance on foot till we came
to a ridge running down the slope, and upon this ridge the lava stream
was flowing.
Above our heads hung a vast cloud of vapour which reflected the bright
light from the red-hot stream, and threw a pink glow all around, so
that, where the cloud was broken and we could see the dark sky, the
stars looked white as silver in contrast. We could now trace clearly the
outline of the summit towering above us, and even watch the showers of
ashes and dust which burst forth from time to time, falling back into
the crater, or on to the steep slopes of the cone.
If the night had not been calm, and such a breeze as there was blowing
away from us, our position would scarcely have been safe; and indeed we
were afterwards told we had been rash. But I would have faced even a
greater risk to see so grand a spectacle, and when the guide helped me
to scramble up on to the ledge, so that I stood with my feet within a
few yards of the lava flow, my heart bounded with excitement. I could
not stay more than a few seconds, for the gases and vapour choked me;
but for that short time it felt like a dream to be standing close to a
river of molten rock, which a few hours before had been lying deep in
the bowels of the earth. Glancing upwards to where this river issued
from the cone in the mountain-side, I saw it first white-hot, then
gradually fading to a glowing red as it crept past my feet; and then
looking down the slope I saw it turn black and gloomy as it cooled
rapidly at the top, while through the cracks which opened here and there
as it moved on, puffs of gas and vapour rose into the air, and the red
lava beneath gleamed through the chinks.
We did not stay long, for the air was suffocating, but took our way back
to the Hermitage, where another glorious sight awaited us. Some way
above and behind the hill on which the Observatory stands there is, or
was, a steep cliff, and over this the lava stream, now densely black,
fell in its way to the valley below, and as it fell it broke into huge
masses, which heeling over exposed the red-hot lava under the crust,
thus forming a magnificent fiery cascade in which black and red were
mingled in wild confusion.
This is how I saw a fresh red-hot lava stream. I had ascended the
mountain some years before, when it was comparatively quiet, with only
two small cones in its central crater sending out miniature flows of
lava (see Fig. 38). But the crater was too hot for me to cross over to
these cones, and I could only marvel at the mass of ashes of which the
top of the mountain was composed, and plunge a stick into an old lava
stream to see how hot it still remained below. Peaceful and quiet as the
mountain seemed then, I could never have imagined such a glorious
outburst as that of November 1868 unless I had seen it, and yet this was
quite a small eruption compared to those of 1867 and 1872, which in
their turn were nothing to some of the older eruptions in earlier
centuries.
[Illustration: Fig. 38.
The top of Vesuvius in 1864. (After Nasmyth.)]
Now it is the history of this lava stream which I saw, that we are going
to consider to-day, and you will first want to know where it came from,
and what caused it to break out on the mountain-side. The truth is, that
though we know now a good deal about volcanoes themselves, we know very
little about the mighty cauldrons deep down in the earth from which
they come. Our deepest mines only reach to a depth of a little more than
half a mile, and no borings even have been made beyond three-quarters of
a mile, so that after this depth we are left very much to guesswork.
We do know that the temperature increases as we go farther down from the
surface, but the increase is very different in different districts--in
some places being five times greater than it is in others at an equal
depth, and it is always greatest in localities where volcanoes have been
active not long before. Now if there were an ocean of melted rock at a
certain distance down below the crust all over the globe, there could
scarcely be such a great difference between one place and another, and
for this and many other reasons geologists are inclined to think that,
from some unknown cause, great heat is developed at special points below
the surface at different times. This would account for our finding
volcanic rocks in almost all parts of the world, even very far away from
where there are any active volcanoes now.
But, as I have said, we do not clearly know why great reservoirs of
melted rock occur from time to time deep under our feet. We may perhaps
one day find the clue from the fact that nearly all, if not all,
volcanoes occur near to the water's edge, either on the coast of the
great oceans or of some enormous inland sea or lake. But at present all
we can say is, that in certain parts of the globe there must be from
time to time great masses of rock heated till they are white-hot, and
having white-hot water mingled with them. These great masses need not,
however, be liquid, for we know that under enormous pressure white-hot
metals remain solid, and water instead of flashing into steam is kept
liquid, pressing with tremendous force upon whatever keeps it confined.
But now suppose that for some reason the mass of solid rock and ground
above one of these heated spots should crack and become weak, or that
the pressure from below should become so great as to be more powerful
than the weight above, then the white-hot rock and water quivering and
panting to expand, would upheave and burst the walls of their prison.
Cannot you picture to yourselves how when this happened the rock would
swell into a liquid state, and how the water would force its way upwards
into cracks and fissures expanding into steam as it went. Then would be
heard strange rumbling noises underground, as all these heavily
oppressed white-hot substances upheaved and rent the crust above them.
And after a time the country round, or the ground at the bottom of the
sea, would quake and tremble, till by and by a way out would be found,
and the water flashing into vapour would break and fling up the masses
of rock immediately above the passage it had made for itself, and
following after these would come the molten rock pouring out at the new
opening.
Such outbursts as these have been seen at sea many times near volcanic
islands. In 1811 a new island called Sabrina was thrown up off St.
Michael's in the Azores, and after remaining a short time was washed
away by the waves. In the same way Graham's Island appeared off the
coast of Sicily in 1831, and as late as 1885 Mr. Shipley saw a
magnificent eruption in the Pacific near the Tonga Islands when an
island about three miles long was formed.
Another very extraordinary outburst, this time on land, took place in
1538 on the opposite side of the Bay of Naples to where Vesuvius stands.
There, on the shores of the Bay of Baiæ, a mountain 440 feet high was
built up in one week, where all had before been quiet in the memory of
man. For two years before the outburst came, rumblings and earthquakes
had alarmed the people, and at last one day the sea drew back from the
shore and the ground sank about fourteen feet, and then on the night of
Sunday, September 29, 1538, it was hurled up again, and steam, fiery
gases, stones, and mud burst forth, driving away the frightened people
from the village of Puzzuoli about two miles distant. For a whole week
jets of lava, fragments of rock, and showers of ashes were poured out,
till they formed the hill now called Monte Nuovo, 440 feet high and
measuring a mile and a half round the base. And there it has remained
till the present day, perfectly quiet after the one great outburst had
calmed down, and is now covered with thickets of stone-pine trees.
These sudden outbursts show that some great change must occur in the
state of the earth's crust under the spots where they take place, and we
know that eruptions may cease for centuries in any particular place and
then begin afresh quite unexpectedly. Vesuvius was a peaceable mountain
overgrown with trees and vines in the time of the Greeks till in the
year A.D. 79 occurred the terrific outburst which destroyed Herculaneum
and Pompeii, shattering old Vesuvius to pieces, so that only the cliffs
on the northwest remain and are called Somma (see Fig. 37), while the
new Vesuvius has grown up in the lap, as it were, of its old self. Yet
when we visit the cliffs of Somma, and examine the old lava streams in
them, we see that the ancient peaceful mountain was itself built up by
volcanic outbursts of molten rock, and showers of clinkers or scoriæ,
long before man lived to record it.
Meanwhile, when once an opening is made, we can understand how after an
eruption is over, and the steam and lava are exhausted, all quiets down
for awhile, and the melted rock in the crater of the mountain cools and
hardens, shutting in once more the seething mass below. This was the
state of the crater when I saw it in 1864, though small streams still
flowed out of two minute cones; but since then at least one great
outburst had taken place in 1867, and now on this November night, 1868,
the imprisoned gases rebelled once more and forced their way through the
mountain-side.
At this point we can leave off forming conjectures and really study what
happens; for we do know a great deal about the structure of volcanoes
themselves, and the history of a lava-flow has been made very clear
during the last few years, chiefly by the help of the microscope and
chemical experiments. If we imagine then that on the day of the eruption
we could have seen the inside of the mountain, the diagram (Fig. 39)
will fairly represent what was taking place there.
[Illustration: Fig. 39.
Diagrammatic section of an active volcano.
_a_, Central pipe or funnel. _b_, _b_, Walls of the crater or cup.
_c_, _c_, Dark turbid cloud formed by the ascending globular clouds
_d_, _d_. _e_, Rain-shower from escaped vapour. _f_, _f_, Shower of
blocks, cooled bombs, stones, and ashes falling back on to the cone.
_g_, Lava escaping through a fissure, and pouring out of a cone opened
in the mountain side.]
In the funnel _a_ which passes down from the crater or cup _b_, _b_,
white-hot lava was surging up, having a large quantity of water and
steam entangled in it. The lava, or melted rock, would be in much the
same state as melted iron-slag is, in the huge blast-furnaces in which
iron-rock is fused, only it would have floating in it great blocks of
solid rock, and rounded stones called bombs which have been formed from
pieces of half-melted rock whirled in air and falling back into the
crater, together with clinkers or scoriæ, dust and sand, all torn off
and ground down from the walls of the funnel up which the rush was
coming. And in the pipe of melted rock, forcing the lava upwards,
enormous bubbles of steam and gas _d_, _d_ would be rising up one after
another as bubbles rise in any thick boiling substances, such as boiling
sugar or tar.
In the morning before the eruption, when only a little smoke was issuing
from the crater, these bubbles rose very slowly through the loaded
funnel and the half-cooled lava in the basin, and the booming noise,
like that of heavy cannon, heard from time to time, was caused by the
bursting of one of these globes of steam at the top of the funnel, as it
brought up with it a feeble shower of stones, dust, and scoriæ.
Meanwhile the lava surging below was forcing a passage _g_ for itself in
a weak part of the mountain-side and, just at the time when our
attention was called to Vesuvius, the violent pressure from below rent
open a mouth or crater at _h_, so that the lava began to flow down the
mountain in a steady stream. This, relieving the funnel, enabled the
huge steam bubbles _d_, _d_ to rise more quickly, and to form the large
whitish-grey cloud _c_, into which from time to time the red-hot blocks,
scoriæ, and pumice were thrown up by the escaping steam and gases. These
blocks and fragments then fell back again in a fiery shower _f_, _f_
either into the cup, to be thrown up again by the bursting of the next
bubble, or on to the sides of the cone, making it both broader and
higher.
Only one feature in the diagram was fortunately absent the evening we
went up, namely, the rain-shower _e_. The night, as I said, was calm,
and the air dry, and the steam floated peacefully away. The next night,
however, when many people hurried down from Rome to see the sight they
were woefully disappointed, for rain-showers fell heavily from the
cloud, bringing down with them the dust and ashes, which covered the
unfortunate sight-seers.
This was what happened during the eruption, and the result after a few
days was that the cone was a little higher, with a fresh layer of rough
slaggy scoriæ on its slopes, and that on the side of the mountain behind
the Hermitage a new lava stream was added to the many which have flowed
there of late years. What then can we learn from this stream about the
materials which come up out of the depths of the earth, and of the
manner in which volcanic rocks are formed?
The lava as I saw it when coming first out of the newly-opened crater
is, as I have said, like white-hot iron slag, but very soon the top
becomes black and solid, a hard cindery mass full of holes and cavities
with rough edges, caused by the steam and sulphur and other gases
breaking through it.[1] In fact, there are so many holes and bubbles in
it that it is very light and floats on the top of the heavier lava
below, falling over it on to the mountain-side when it comes to the end
of the stream. Still, however, the great mass moves on, so that the
stream slides over these fallen clinkers or scoriæ. Thus after an
eruption a new flow consists of three layers; at the top the cooled and
broken crust of clinkers, then the more solid lava, which often remains
hot for years, and lastly another cindery layer beneath, formed of the
scoriæ which have fallen from above (see Fig. 40).
[1] For the cindery nature of the surface of such a stream see the
initial letter of this chapter.
[Illustration: Fig. 40.
Section of a lava-flow. (J. Geikie.)
1, Slaggy crust, formed chiefly of scoriæ of a glassy nature. 2, Middle
portion where crystals form. 3, Slaggy crust which has slipped down and
been covered by the flow.]
You would be surprised to see how quickly the top hardens, so that you
can actually walk across a stream of lava a day or two after it comes
out from the mountain. But you must not stand still or your shoes would
soon be burnt, and if you break the crust with a stick you will at once
see the red-hot lava below; while after a few days the cavities become
filled with crystals of common salt, sulphur or soda, as the vapour and
gases escape.
Then as time goes on the harder minerals gradually crystallise out of
the melted mass, and iron-pyrites, copper-sulphate, and numerous other
forms of crystal appear in the lower part of the stream. In the clinkers
above, where the cooling goes on very rapidly, the lavas formed are
semi-transparent and look much like common bottle-glass. In fact, if you
take this piece of obsidian or volcanic glass in your hand, you might
think that it had come out of an ordinary glass manufactory and had
nothing remarkable in it.
[Illustration: Fig. 41.
A slice of volcanic glass showing the lines of crystallites and
microliths which are the beginnings of crystals.[1] (J. Geikie.)]
[1] This arrangement in lines is called _fluidal structure_ in lava.
But the microscope tells another tale. I have put a thin slice under the
first microscope, and this diagram (Fig. 41) shows what you will see.
Nothing, you say, but a few black specks and some tiny dark rods. True,
but these specks and rods are the first beginnings of crystals forming
out of the ground-mass of glassy lava as it cools down. They are not
real crystals, but the first step toward them, and by a careful
examination of glassy lavas which have cooled at different rates, they
have been seen under the microscope in all stages of growth, gradually
building up different crystalline forms. When we remember how rapidly
the top of many glassy lavas cool down we can understand that they have
often only time to grow very small.
[Illustration: Fig. 42.
A slice of volcanic glass under the microscope, showing well-developed
microliths. (After Cohen.)]
The smaller specks are called _crystallites_, the rods are called
_microliths_.[1] Under the next microscope you can see the microliths
much more distinctly (Fig. 42) and observe that they grow in very
regular shapes.
[1] _Micros_, little; _lithos_, stone.
Our first slice, however (Fig. 41), tells us something more of their
history, for the fact that they are arranged in lines shows that they
have grown while the lava was flowing and carrying them along in
streams. You will notice that each one has its greatest length in the
direction of the lines, just as pieces of stick are carried along
lengthways in a river. In the second specimen (Fig. 42) the microliths
are much larger and the stream has evidently not been flowing fast, for
they lie in all directions.
This is what we find in the upper part of the stream, but if we look at
a piece of underlying lava we find that it is much more coarse-grained,
and the magnifying-glass shows many crystals in it, as well as a number
of microliths. For this lava, covered by the crust above, has remained
very hot for a long time, and the crystals have had time to build
themselves up out of the microliths and crystallites.
Still there is much glassy groundwork even in these lavas. If we want to
find really stony masses such as porphyry and granite made up entirely
of crystals we must look inside the mountain where the molten rock is
kept intensely hot for long periods, as for example in the fissure _g_,
Fig. 39.
Such fissures sometimes open out on the surface like the one I saw, and
sometimes only penetrate part of the way through the hill; but in either
case when the lava in them cools down, it forms solid walls called dykes
which help to bind the loose materials of the mountain together. We
cannot, of course, examine these in an active volcano, but there are
many extinct volcanoes which have been worn and washed by the weather
for centuries, so that we can see the inside. The dykes laid bare in the
cliffs of Somma are old fissures filled with molten rock which has
cooled down, and they show us many stony lavas; and Mr. Judd tells us of
one beautiful example of a ruined volcano which composes the whole
island of Mull in the Hebrides, where such dykes can be traced right
back to a centre. This centre must once have been a mass of melted
matter far down in the earth, and as you trace the dykes back deeper and
deeper into it, the rocks grow more and more stony, till at last they
are composed entirely of large crystals closely crowded together
without any glassy matter between them. You know this crystalline
structure well, for we have plenty of blocks of granite scattered about
on Dartmoor, showing that at some time long ago molten matter must have
been at work in the depths under Devonshire.
We see then that we can trace the melted rock of volcanoes right
back--from the surface of the lava stream which cools quickly at the
top, hurrying the crystallites and microliths along with it--down
through the volcano to the depths of the earth, where the perfect
crystals form slowly and deliberately in the underground lakes of
white-hot rock which are kept in a melted state at an intense heat.
[Illustration: Fig. 43.
A piece of Dartmoor Granite, drawn from a specimen.]
But I promised you that we would have no guesswork here, and you will
perhaps ask how I can be certain what was going on in the depths when
these crystals were formed. A few years ago I could not have answered
you, but now chemists, and especially two eminent French chemists, MM.
Fouqué and Levy, have actually _made_ lavas and shown us how it is done
in Nature.
By using powerful furnaces and bellows they have succeeded in getting
temperatures of all degrees, from a dazzling white heat down to a dull
red, and to keep any temperature they like for a long time, so as to
imitate the state of a mass of melted rock at different depths in the
earth, and in this way they have actually _made_ lavas in their
crucibles. For example, there is a certain whitish rock common in
Vesuvius called _leucotephrite_,[1] which is made up chiefly of crystals
of the minerals called leucite, Labrador felspar, and augite. This they
proposed to make artificially, so they took proper quantities of silica,
alumina, oxide of iron, lime, potash, and soda, and putting them in a
crucible, melted them by keeping them at a white heat. Then they lowered
the temperature to an orange-heat, that is a heat sufficient to melt
steel. They kept this heat for forty-eight hours, after which they took
out some of the mixture and, letting it cool, examined a slice under the
microscope. Within it they found crystals of _leucite_ already formed,
showing that these are the first to grow while the melted rock is still
intensely hot. The rest of the mixture they kept red-hot, or at the
melting-point of copper, for another forty-eight hours, and when they
took it out and examined it they found that the whole of it had been
transformed into microliths of the two other forms of crystals, Labrador
felspar and augite, except some small eight-sided crystals of magnetite
and picotite which are also found in the natural rock.
[1] _Leucos_, white; _tephra_, ashes.
There is no need for you to remember all these names. What I do want you
to remember is, that, at the different temperatures, the right crystals
and beginnings of crystals grew up to form the rock which is found in
Vesuvius. And what is still more interesting, they grew exactly to the
same stages as in the natural rock, which is composed of _crystals_ of
leucite and _microliths_ of the two other minerals.
This is only one among numerous experiments by which we have learnt how
volcanic rocks are formed and at what heat the crystals of different
substances grow. We are only as yet at the beginning of this new study,
and there is plenty for you boys to do by and by when you grow up. Many
experiments have failed as yet to imitate certain rocks, and it is
remarkable that these are usually rocks of very ancient eruptions, when
_perhaps_ our globe may have been in a different state to what it is
now; but this remains for us to find out.
Meanwhile I have still another very interesting slide to show you which
tells us something of what is going on below the volcano. Under the
third microscope I have put a slice of volcanic glass (Fig. 44) in which
you will see really large crystals with dark bands curving round them.
These crystals have clearly not been formed in the glass while the lava
was flowing, first because they are too large to have grown up so
rapidly, and secondly because they are broken at the edges in places and
sometimes partly melted. They have evidently come up with the lava as it
flowed out of the mountain, and the dark bands curving round them are
composed of microliths which have been formed in the flow and have swept
round them, as floating straws gather round a block of wood in a stream.
Such crystals as these are often found in lava streams, and in fact they
make a great difference in the rate at which a stream flows, for a
thoroughly melted lava shoots along at a great pace and often travels
several miles in a very short time; but an imperfectly melted lava full
of crystals creeps slowly along, and often does not travel far from the
crater out of which it flows.
[Illustration: Fig. 44.
Slice of volcanic glass under the microscope, showing large included
crystals brought up from inside the volcano in the fluid lava. The dark
bands are lines of microliths formed as the lava cooled. (J. Geikie.)]
So you see we have proof in this slice of volcanic glass of two separate
periods of crystallisation--the period when the large crystals grew in
the liquid mass under the mountain, and the period when the microliths
were formed after it was poured out above ground. And as we know that
different substances form their crystals at very different temperatures,
it is not surprising that some should be able to take up the material
they require and grow in the underground lakes of melted matter, even
though the rest of the lava was sufficiently fluid to be forced up out
of the mountain.
And here we must leave our lava stream. The microscope can tell us yet
more, of marvellous tiny cavities inside the crystals, millions in a
single inch, and of other crystals inside these, all of which have their
history; but this would lead us too far. We must be content for the
present with having roughly traced a flow of lava from the depths below,
where large crystals form in subterranean darkness, to the open air
above, where we catch the tiny beginnings of crystals hardened into
glassy lava before they have time to grow further.
If you will think a little for yourselves about these wonderful
discoveries made with the magic-glass, you will see how many questions
they suggest to us about the minerals which we find buried in the earth
and running through it in veins, and you will want to know something
about the more precious crystals, such as rubies, diamonds, sapphires,
and garnets, and many others which Nature forms far away out of our
sight. All these depend, though indirectly, upon the strange effects of
underground heat, and if you have once formed a picture in your minds of
what must have been going on before that magnificent lava stream crept
down the mountain-side and added its small contribution to the surface
of the earth, you will study eagerly all that comes in your way about
crystals and minerals, and while you ask questions with the spectroscope
about what is going on in the sun and stars millions of miles away, you
will also ask the microscope what it has to tell of the work going on at
depths many miles under your feet.
CHAPTER VI
AN HOUR WITH THE SUN
[Illustration]
Before beginning upon the subject of our lecture to-day I want to tell
you the story of a great puzzle which presented itself to me when I was
a very young child. I happened to come across a little book--I can see
it now as though it were yesterday--a small square green book called
_World without End_, which had upon the cover a little gilt picture of a
stile with trees on each side of it. That was all. I do not know what
the book was about, indeed I am almost sure I never opened it or saw it
again, but that stile and the title "World without End" puzzled me
terribly. What was on the other side of the stile? If I could cross over
it and go on and on should I be in a world which had no ending, and what
would be on the other side? But then there could be no other side if it
was a world without any end. I was very young, you must remember, and I
grew confused and bewildered as I imagined myself reaching onwards and
onwards beyond that stile and never, never resting. At last I consulted
my greatest friend, an old man who did the weeding in my father's
garden, and whom I believed to be very wise. He looked at first almost
as bewildered as I was, but at last light dawned upon him. "I tell you
what it is, Master Arthur," said he, "I do not rightly know what happens
when there is no end, but I do know that there is a mighty lot to be
found out in this world, and I'm thinking we had better learn first all
about that, and perhaps it may teach us something which will help us to
understand the other."
I daresay you will wonder what this anecdote can have to do with a
lecture on the sun--I will tell you. Last night I stood on the balcony
and looked out far and farther away into the star-depths of the midnight
sky, marvelling what could be the history of those countless suns of
which we see ever more and more as we increase the power of our
telescopes, or catch the faint beams of those we cannot see and make
them print their image on the photographic plate. And, as I grew
oppressed at the thought of this never-ending expanse of suns and at my
own littleness, I remembered all at once the little square book of my
childish days with its gilt stile, and my old friend's advice to learn
first all we can of that which lies nearest.
So to-day, before we travel away to the stars, we had better inquire
what is known about the one star in the heavens which is comparatively
near to us, our own glorious sun, which sends us all our light and heat,
causes all the movements of our atmosphere, draws up the moisture from
the ground to return in refreshing rain, ripens our harvests, awakens
the seeds and sleeping plants into vigorous growth, and in a word
sustains all the energy and life upon our earth. Yet even this star,
which is more than a million times as large as our earth, and bound so
closely to us that a convulsion on its surface sends a thrill right
through our atmosphere, is still so far off that it is only by
questioning the sunbeams it sends to us, that we can know anything about
it.
You have already learnt[1] a good deal as to the size, the intense heat
and light, and the photographic power of the sun, and also how his white
beams of light are composed of countless coloured rays which we can
separate in a prism. Now let us pass on to the more difficult problem of
the nature of the sun itself, and what we know of the changes and
commotions going on in that blazing globe of light.
[1] _Fairyland of Science_, Chapter II.
We will try first what we can see for ourselves. If you take a card and
make a pin-hole in it, you can look through this hole straight at the
sun without injuring your eye, and you will see a round shining disc on
which, perhaps, you may detect a few dark spots. Then if you take your
hand telescopes, which I have shaded by putting a piece of smoked glass
inside the eye-piece, you will find that this shining disc is really a
round globe, and moreover, although the object-glass of your telescopes
measures only two-and-a-half inches across, you will be able to see the
dark spots very distinctly and to observe that they are shaded, having a
deep spot in the centre with a paler shadow round it.
[Illustration: Fig. 45.
Face of the sun projected on a sheet of cardboard C. T, Telescope. _f_,
Finder. _og_, Object-glass. _ep_, Eye-piece. S, Screen shutting off the
diffused light from the window.]
As, however, you cannot all use the telescopes, and those who can will
find it difficult to point them truly on to the sun, we will adopt still
another plan. I will turn the object-glass of my portable telescope full
upon the sun's face, and bringing a large piece of cardboard on an easel
near to the other end, draw it slowly backward till the eye-piece forms
a clear sharp image upon it (see Fig. 45). This you can all see
clearly, especially as I have passed the eye-piece of the telescope
through a large screen _s_, which shuts off the light from the window.
You have now an exact image of the face of the sun and the few dark
spots which are upon it, and we have brought, as it were, into our room
that great globe of light and heat which sustains all the life and
vigour upon our earth.
This small image can, however, tell us very little. Let us next see what
photography can show us. The diagram (Fig. 46) shows a photograph of the
sun taken by Mr. Selwyn in October 1860. Let me describe how this is
done. You will remember that there is a point in the telescope tube
where the rays of light form a real image of the object at which the
telescope is pointed (see p. 44). Now an astronomer who wishes to take a
photograph of the sun takes away the eye-piece of his telescope and puts
a photographic plate in the tube exactly at the place where this real
image is formed. He takes care to blacken the frame of the plate and
shuts up this end of the telescope and the plate in a completely dark
box, so that no diffused light from outside can reach it. Then he turns
his telescope upon the sun that it may print its image.
But the sun's light is so strong that even in a second of time it would
print a great deal too much, and all would be black and confused. To
prevent this he has a strip of metal which slides across the tube of the
telescope in front of the plate, and in the upper part of this strip a
very fine slit is cut. Before he begins, he draws the metal up so that
the slit is outside the tube and the solid portion within, and he
fastens it in this position by a thread drawn through and tied to a bar
outside. Then he turns his telescope on the sun, and as soon as he
wishes to take the photograph he cuts the thread. The metal slides
across the tube with a flash, the slit passing across it and out again
below in the hundredth part of a second, and in that time the sun has
printed through the slit the picture before you.
[Illustration: Fig. 46.
Photograph of the face of the sun, taken by Mr. Selwyn, October 1860,
showing spots, faculæ, and mottled surface.]
In it you will observe at least two things not visible on our
card-image. The spots, though in a different position from where we see
them to-day, look much the same, but round them we see also some bright
streaks called _faculæ_, or torches, which often appear in any region
where a spot is forming, while the whole face of the sun appears mottled
with bright and darker spaces intermixed. Those of you who have the
telescopes can see this mottling quite distinctly through them if you
look at the sun. The bright points have been called by many names, and
are now generally known as "light granules," as good a name, perhaps, as
any other.
This is all our photograph can tell us, but the round disc there shown,
which is called the _photosphere_, or light-giving sphere, is by no
means the whole of the sun, though it is all we see daily with the naked
eye. Whenever a total eclipse of the sun takes place--by the dark body
of the moon coming between us and it, so as to shut out the whole of
this disc--a brilliant white halo, called the crown or _corona_, is seen
to extend for many thousands of miles all round the darkened globe. It
varies very much in shape, sometimes forming a kind of irregular square,
sometimes a circle with off-shoots, as in Fig. 47, which shows what
Major Tennant saw in India during the total eclipse of August 18, 1868,
and at other times it shoots out in long pearly white jets and sheets of
light with dark spaces between. On the whole it varies periodically. At
the time of few sun-spots its extensions are equatorial; but when the
sun's face is much covered with spots, they are diagonal, stretching
away from the spot-zones, but not nearly so far.
[Illustration: Fig. 47.
Total eclipse of the sun, as drawn by Major Tennant at Guntoor in India,
August 18, 1868, showing corona and the protuberances seen at the
beginning of totality.]
And besides this corona there are seen very curious flaming projections
on the edge of the sun, which begin to appear as soon as the moon covers
the bright disc. In our diagram (Fig. 47) you see them on the left side
where the moon is just creeping over the limits of the photosphere and
shutting out the strong light of the sun as the eclipse becomes total. A
very little later they are better seen on the other side just before the
bright edge of the sun is uncovered as the moon passes on its way. These
projections in the real sun are of a bright red colour, and they take on
all manners of strange shapes, sometimes looking like ranges of fiery
hills, sometimes like gigantic spikes and scimitars, sometimes even like
branching fiery trees. They were called _prominences_ before their
nature was well understood, and will probably always keep that name. It
would be far better, however, if some other name such as "glowing
clouds" or "red jets" could be used, for there is now no doubt that they
are jets of gases, chiefly hydrogen, constantly playing over the face of
the sun, though only seen when his brighter light is quenched. They have
been found to shoot up 20,000, 80,000, and even as much as 350,000 miles
beyond the edge of the shining disc; and this last means that the flames
were so gigantic that if they had started from our earth they would have
reached beyond the moon. We shall see presently that astronomers are now
able by the help of the spectroscope to see the prominences even when
there is no eclipse, and we know them to be permanent parts of the
bright globe.
This gives us at last the whole of the sun, so far as we know. There is,
indeed, a strange faint zodiacal light, a kind of pearly glow seen after
sunset or before sunrise extending far beyond the region of the corona;
but we understand so little about this that we cannot be sure that it
actually belongs to the sun.
And now how shall I best give you an idea of what little we do know
about this great surging monster of light and heat which shines down
upon us? You must give me all your attention, for I want to make the
facts quite clear, that you may take a firm hold upon them.
Our first step is to question the sunlight which comes to us; and this
we do with the spectroscope. Let me remind you how we read the story of
light through this instrument. Taking in a narrow beam of light through
a fine slit, we pass the beam through a lens to make the rays parallel,
and then throw it upon a prism or row of prisms, so that each set of
waves of coloured light coming through the slit is bent on its own road
and makes an upright image of the slit on any screen or telescope put to
receive it (see Fig. 21, p. 52). Now when the light we examine comes
from a glowing solid, like white-hot iron, or a glowing liquid, or a gas
under such enormous pressure that it behaves like a liquid, then the
images of the slit always overlap each other, so that we see a
continuous unbroken band of colour. However much you spread out the
light you can never break up or separate the spectrum in any part.[1]
But when you send the light, of a glowing gas such as hydrogen through
the spectroscope, or of a substance melted into gas or vapour, such as
sodium or iron vaporised by great heat, then it is a different story.
Such gases give only a certain number of bright lines quite separate
from each other on the dark background, and each kind of gas gives its
own peculiar lines; so that even when several are glowing together there
is no confusion, but when you look at them through the spectroscope you
can detect the presence of each gas by its own lines in the spectrum.
[1] Two rare earths, Erbia and Didymium, form an exception to this,
but they do not concern us here.
[Illustration: TABLE OF SPECTRA. Plate I.]
To make quite sure of this we will close the shutters and put a pinch of
salt in a spirit-flame. Salt is chloride of sodium, and in the flame the
sodium glows with a bright yellow light. Look at this light through your
small direct-vision spectroscopes[1] and you see at once the bright
yellow double-line of sodium (No. 3, Plate I.) start into view across
the faint continuous spectrum given by the spirit-flame. Next I will
show you glowing hydrogen. I have here a glass tube containing hydrogen,
so arranged that by connecting two wires fastened to it with the
induction coil of our electric battery it will soon glow with a bright
red colour. Look at this through your spectroscopes and you will see
three bright lines, one red, one greenish blue, and one indigo blue,
standing out on the dark background (No. 4, Plate I.)
[1] A direct-vision spectroscope is like a small telescope with
prisms arranged inside the tube. The object-glass end is covered by
two pieces of metal, which slide backwards and forwards by means of
a screw, so that a narrow or broad slit can be opened.
Think for a moment what a grand power this gives you of reading as in a
book the different gases which are glowing in the sky even billions of
miles away. You would never mistake the lines of hydrogen for the line
of sodium, but when looking at a nebula or any mass of glowing gas you
could say at once "sodium is glowing there," or "that cloud must be
composed of hydrogen."
Now, opening the shutters, look at the sunlight through your
spectroscopes. Here you have something different from either the
continuous spectrum of solids, or the bright separate lines of gases,
for while you have a bright-coloured band you have also some dark lines
crossing it (No. 2, Plate I.) It is those dark lines which enable us to
guess what is going on in the sun before the light comes to us. In 1859
Professor Kirchhoff made an experiment which explained those dark lines,
and we will repeat it now. Take a good look at the sunlight spectrum, to
fix the lines in your memory, and then close the shutters again.
[Illustration: Fig. 48.
Kirchhoff's experiment, explaining the dark lines in sunlight.
A, Limelight dispersed through a prism. _s_, Slit through which the beam
of light comes. _l_, Lens bringing it to a focus on the prism _p_. _sp_,
Continuous spectrum thrown on the wall. B, The same light, with the
flame _f_ containing glowing sodium placed in front of it. D, Dark
sodium line appearing in the spectrum.]
I have here our magic-lantern with its lime-light, in which the solid
lime glows with a white heat, in consequence of the jets of oxygen and
hydrogen burning round it. This was the light Kirchhoff used, and you
know it will give a continuous bright band in the spectroscope. I put a
cap with a narrow slit in it over the lantern tube, so as to get a
narrow beam of light; in front of this I put a lens _l_, and in front of
this again the prism _p_. The slit and the prism act exactly like your
spectroscopes, and you can all see the continuous spectrum on the screen
(_sp_, A, Fig. 48). Next I put a lighted lamp of very weak spirit in
front of the slit, and find that it makes no difference, for whatever
light it gives only strengthens the spectrum. But now notice carefully.
I am going to put a little salt into the flame, and you would expect
that the sodium in it, when turned to glowing vapour, causing it to look
yellow, would strengthen the yellow part of the spectrum and give a
bright line. This is what Kirchhoff expected, but to his intense
surprise he saw as you do now a _dark line_ D start out where the bright
line should have been.
What can have happened? It is this. The oxyhydrogen light is very hot
indeed, the spirit flame with the sodium is comparatively weak and cool.
So when those special coloured waves of the oxyhydrogen light which
agree with those of the sodium light reached the flame, they spent all
their energy in heating up those waves to their own temperature, and
while all the other coloured rays travelled on and reached the screen,
these waves were stopped or _absorbed_ on the way, and consequently
there was a blank, black space in the spectrum where they should have
been. If I could put a hydrogen flame cooler than the original light in
the road, then there would be three dark lines where the bright hydrogen
lines should be, and so with every other gas. _The cool vapour in front
of the hot light cuts off from the white ray exactly those waves which
it gives out itself when burning._
Thus each black line of the sun-spectrum (No. 2, Plate I.), tells us
that some particular ray of sunlight has been absorbed by a cooler
vapour _of its own kind_ somewhere between the sun and us, and it must
be in the sun itself, for when we examine other stars we often find dark
lines in their spectrum different from those in the sun, and this shows
that the missing rays must have been stopped close at home, for if they
were stopped in our atmosphere they would all be alike.
There are, by the bye, some lines which we know are caused by our
atmosphere, especially when it is full of invisible water vapour, and
these we easily detect, because they show more distinctly when the sun
is low and shines through a thicker layer of air than when he is high up
and shines through less.
But to return to the sun. In your small spectroscopes you see very few
dark lines, but in larger and more perfect ones they can be counted by
thousands, and can be compared with the bright lines of glowing gases
burnt here on earth. In the spectrum of glowing iron vapour 460 lines
are found to agree with dark lines in the sun-spectrum, and other gases
have nearly as many. Still, though thousands of lines can now be
explained, by matching them with the bright lines of known gases, the
whole secret of sunlight is not yet solved, for the larger number of
lines still remain a riddle to be read.
We see then that the spectroscope teaches us that the round light-giving
disc or photosphere of the sun consists of a bright and intensely hot
light shining behind a layer of cooler though still very hot vapours,
which form a kind of shell of luminous clouds around it, and in this
shell, or _reversing layer_--as it is often called, because it turns
light to darkness--we have proved that iron, lead, copper, zinc,
aluminum, magnesium, potassium, sodium, carbon, hydrogen, and many other
substances common to our earth, exist in a state of vapour for a depth
of perhaps 1000 miles.
You will easily understand that when the spectroscope had told so much,
astronomers were eager to learn what it would reveal about the
prominences or red jets seen during eclipses, and they got an answer in
India during that same eclipse of August 1868 which is shown in our
diagram (Fig. 47). Making use of the time during which the prominences
were seen, they turned the telescope upon them with a spectroscope
attached to it, and saw a number of bright lines start out, of which the
chief were the three bright lines of hydrogen, showing that these
curious appearances are really flames of glowing gas.
In the same year Professor Jannsen and Mr. Lockyer succeeded in seeing
the bright lines of the prominences in full sunlight. This was done in a
very simple way, when once it was discovered to be possible, and though
my apparatus (Fig. 49) is very primitive compared with some now made, it
will serve to explain the method.
[Illustration: Fig. 49.
The spectroscope attached to the telescope for the examination of the
sun. (Lockyer.)
P, Pillar of Telescope. T, Telescope. S, Finder or small telescope for
pointing the telescope in position. _a_, _a_, _b_, Supports fastening
the spectroscope to the telescope. _d_, Collimator or tube carrying the
slit at the end nearest the telescope, and a lens at the other end to
render the rays parallel. _c_, Plate on which the prisms are fixed. _e_,
Small telescope through which the observer examines the spectrum after
the ray has been dispersed in the prisms. _h_, Micrometer for measuring
the relative distance of the lines.]
When an astronomer wishes to examine the spectrum of any special part of
the sun, he takes off the eye-piece of his telescope and screws the
spectroscope upon the draw-tube. The spectroscope is made exactly like
the large one for ordinary work. The tube _d_ (Fig. 49) carries the slit
at the end nearest the telescope, and this slit must be so placed as to
stand precisely at the principal focus of the lens where the sun's image
is formed (see _i_, _i_, p. 44). This comes to exactly the same thing as
if we could put the slit close against the face of the sun, so as to
show only the small strip which it covers, and by moving it to one part
or another of the image we can see any point that we wish and no other.
The light then passes through the tube _d_ into the round of prisms
standing on the tray _c_, and the observer looking through the small
telescope _e_ sees the spectrum as it emerges from the last prism. In
this way astronomers can examine the spectrum of a spot, or part of a
spot, or of a bright streak, or any other mark on the sun's face.
Now in looking at the prominences we have seen that the difficulty is
caused by the sunlight, between us and them, overpowering the bright
lines of the gas, nor could we overcome this if it were not for a
difference which exists between the two kinds of light. The more you
disperse or spread out the continuous sun-spectrum the fainter it
becomes, but in spreading out the bright lines of the gas you only send
them farther and farther apart; they themselves remain almost as bright
as ever. So, when the telescope forms an image of the red flame in front
of the slit, though the glowing gas and the sunlight both send rays into
the spectroscope, you have only to use enough prisms and arrange them in
such a way that the sunlight is dispersed into a very long faint
spectrum, and then the bright lines of the flames will stand out bright
and clear. Of course only a small part of the long spectrum can be seen
at once, and the lines must be studied separately. On the other hand, if
you want to compare the strong light of the sun with the bright lines of
the prominences, you place the slit just at the edge of the sun's image
in the telescope, so that half the slit is on the sun's face and half on
the prominence. The prisms then disperse the sunlight between you and
the prominences, while they only lessen the strong light of the sun
itself, which still shows clearly. In this way the two spectra are seen
side by side and the dark and bright lines can be compared accurately
together (see Fig. 50).
[Illustration: Fig. 50.
Bright lines of prominences.
Sun-spectrum with dark lines.]
Wherever the telescope is turned all round the sun the lines of luminous
gas are seen, showing that they form a complete layer outside the
photosphere, or light-giving mass, of the sun. This layer of luminous
gases is called the _chromosphere_, or coloured sphere. It lies between
the photosphere and the corona, and is supposed to be at least 5000
miles deep, while, as we have seen, the flames shoot up from it to
fabulous heights.
The quiet red flames are found to be composed of hydrogen and another
new metal called helium; but lower down, near the sun's edge, other
bright lines are seen, showing that sodium, magnesium, and other metals
are there, and when violent eruptions occur these often surge up and
mingle with the purer gas above. At other times the eruptions below
fling the red flames aloft with marvellous force, as when Professor
Young saw a long low-lying cloud of hydrogen, 100,000 miles long, blown
into shreds and flung up to a height of 200,000 miles, when the
fragments streamed away and vanished in two hours. Yet all these violent
commotions and storms are unseen by us on earth unless we look through
our magic glasses.
You will wonder no doubt how the spectroscope can show the height and
the shape of the flames. I will explain to you, and I hope to show them
you one day. You must remember that the telescope makes a small real
image of the flame at its focus, just as in one of our earlier
experiments you saw the exact image of the candle-flame upside down on
the paper (see p. 33). The reason why we only see a strip of the flame
in the spectroscope is because the slit is so narrow. But when once the
sunlight was dispersed so as no longer to interfere, Dr. Huggins found
that it is possible to open the slit wide enough to take in the image of
the whole flame, and then, by turning the spectroscope so as to bring
one of the bright hydrogen lines into view, the actual shape of the
prominence is seen, only it will look a different colour, either red,
greenish-blue, or indigo-blue, according to the line chosen. As the
image of the whole sun and its appendages in the telescope is so very
small, you will understand that even a very narrow slit will really take
in a very large prominence several thousand miles in length. Fig 51
shows a drawing by Mr. Lockyer of a group of flames he observed very
soon after Dr. Huggins suggested the open slit, and these shapes did not
last long, for in another picture he drew ten minutes later their
appearance had already changed.
[Illustration: Fig. 51.
Red prominences, as drawn by Mr. Lockyer during the total eclipse of
March 14, 1869.]
These then are some of the facts revealed to us by our magic glasses. I
scarcely expect you to remember all the details I have given you, but
you will at least understand now how astronomers actually penetrate into
the secrets of the sun by bringing its image into their observatory, as
we brought it to-day on the card-board, and then making it tell its own
tale through the prisms of the spectroscope; and you will retain some
idea of the central light of the sun with its surrounding atmosphere of
cooler gases and its layer of luminous lambent gases playing round it
beyond.
Of the corona I cannot tell you much, except that it is far more subtle
than anything we have spoken of yet; that it is always strongest when
the sun is most spotted; that it is partly made up of self-luminous
gases whose bright lines we can see, especially an unknown green ray;
while it also shines partly by reflected light from the sun, for we can
trace in it faint dark lines; lastly it fades away into the mysterious
zodiacal light, and so the sun ends in mystery at its outer fringe as it
began at its centre.
And now at last, having learnt something of the material of the sun, we
can come back to the spots and ask what is known about them. As I have
said, they are not always the same on the sun's face. On the contrary,
they vary very much both in number and size. In some years the sun's
face is quite free from them, at others there are so many that they form
two wide belts on each side of the sun's equator, with a clear space of
about six degrees between. No spots ever appear near the poles. Herr
Schwabe, who watched the sun's face patiently for more than thirty
years, has shown that it is most spotted about every eleven years, then
the spots disappear very quickly and reappear slowly till the full-spot
time comes round again.
Some spots remain a very short time and then break up and disappear, but
others last for days, weeks, and even months, and when we watch these,
we find that a spot appears to travel slowly across the face of the sun
from east to west and then round the western edge so that it disappears.
It is when it reaches the edge that we can convince ourselves that the
spot is really part of the sun, for there is no space to be seen between
them, the edge and the spot are one, as the last trace of the dark
blotch passes out of sight. In fact, it is not the spot which has
crossed the sun's face, but the sun itself which has turned, like our
earth, upon its axis, carrying the spot round with it. As some spots
remain long enough to reappear, after about twelve or thirteen days, on
the opposite edge, and even pass round two or three times, astronomers
can reckon that the sun takes about twenty-five days and five hours in
performing one revolution. You will wonder why I say only _about_
twenty-five, but I do so because all spots do not come round in exactly
the same time, those farthest from the equator lag rather more than a
day behind those nearer to it, and this is explained by the layer of
gases in which they are formed, drifting back in higher latitudes as the
sun turns.
It is by watching a spot as it travels across the sun, that we are able
to observe that the centre partlies deeper in the sun's face than the
outer rim. There are many ways of testing this, and you can try one
yourselves with a telescope if you watch day after day. I will explain
it by a simple experiment. I have here a round lump of stiff dough, in
which I have made a small hollow and blackened the bottom with a drop of
ink. As I turn this round, so that the hollow facing you moves from
right to left, you will see that after it passes the middle of the face,
the hole appears narrower and narrower till it disappears, and if you
observe carefully you will note that the dark centre is the first thing
you lose sight of, while the edges of the cup are still seen, till just
before the spot disappears altogether. But now I will stick a wafer on,
and a pea half into, the dough, marking the centre of each with ink.
Then I turn the ball again. This time you lose sight of the foremost
edge first, and the dark centre is seen almost to the last moment. This
shows that if the spots were either flat marks, or hillocks, on the
sun's face, the dark centre would remain to the last, but as a fact it
disappears before the rim. Father Secchi has tried to measure the depth
of a spot-cavity, and thinks they vary from 1000 to 3000 miles deep. But
there are many difficulties in interpreting the effects of light and
shadow at such an enormous distance, and some astronomers still doubt
whether spots are really depressions.
For many centuries now the spots have been watched forming and
dispersing, and this is roughly speaking what is seen to happen. When
the sun is fairly clear and there are few spots, these generally form
quietly, several black dots appearing and disappearing with bright
streaks or _faculæ_ round their edge, till one grows bigger than the
rest, and forms a large dark nucleus, round which, after a time, a
half-shadow or _penumbra_ is seen and we have a sun-spot complete, with
bright edges, dark shadow, and deep black centre (Fig. 52). This lasts
for a certain time and then it becomes bridged over with light streaks,
the dark spot breaks up and disappears, and last of all the half-shadow
dies away.
[Illustration: Fig. 52.
A quiet sun-spot. (Secchi.)]
But things do not always take place so quietly. When the sun's face is
very troubled and full of spots, the bright _faculæ_, which appear with
a spot, seem to heave and wave, and generally several dark centres form
with whirling masses of light round them, while in some of them tongues
of fire appear to leap up from below (Fig. 53). Such spots change
quickly from day to day, even if they remain for a long time, until at
last by degrees the dark centres become less distinct, the half-shadows
disappear, leaving only the bright streaks, which gradually settle down
into luminous points or _light granules_. These light granules are in
fact supposed by astronomers to be the tips of glowing clouds heaving up
everywhere, while the dark spaces between them are cooler currents
passing downwards.
[Illustration: Fig. 53.
A tumultuous sun-spot. (Langley.)]
Below these clouds, no doubt, the great mass of the sun is in a violent
state of heat and commotion, and when from time to time, whether
suddenly or steadily, great upheavals and eruptions take place, bright
flames dart up and luminous clouds gather and swell, so that long
streaks or _faculæ_ surge upon the face of the sun.
Now these hot gases rising up thus on all sides would leave room below
for cooler gases to pour down from above, and these, as we know, would
cut off, or absorb, much of the light coming from the body of the sun,
so that the centre, where the down current was the strongest, would
appear black even though some light would pass through. This is the best
explanation we have as yet of the formation of a sun-spot, and many
facts shown in the spectroscope help to confirm it, as for example the
thickening of the dark lines of the spectrum when the slit is placed
over the centre of a spot, and the flashing out of bright lines when an
uprush of streaks occurs either across the spots or round it.
And now, before you go, I must tell you of one of these wonderful
uprushes, which sent such a thrill through our own atmosphere, as to
tell us very plainly the power which the sun has over our globe. The
year 1859 was remarkable for sun-spots, and on September 1, when two
astronomers many miles apart were examining them, they both saw, all at
once, a sudden cloud of light far brighter than the general surface of
the sun burst out in the midst of a group of spots. The outburst began
at eight minutes past eleven in the forenoon, and in five minutes it was
gone again, but in that time it had swept across a space of 35,000 miles
on the sun! Now both before and after this violent outburst took place
a magnetic storm raged all round the earth, brilliant auroras were seen
in all parts of the world, sparks flashed from the telegraph wires, and
the telegraphic signalmen at Washington and Philadelphia received severe
electric shocks. Messages were interrupted, for the storm took
possession of the wires and sent messages of its own, the magnetic
needles darting to and fro as though seized with madness. At the
very instant when the bright outburst was seen in the sun, the
self-registering instruments at Kew marked how three needles jerked all
at once wildly aside; and the following night the skies were lit up with
wondrous lights as the storm of electric agitation played round the
earth.
We are so accustomed to the steady glow of sunshine pouring down upon us
that we pay very little heed to daylight, though I hope none of us are
quite so ignorant as the man who praised the moon above the sun, because
it shone in the dark night, whereas the sun came in the daytime when
there was light enough already! Yet probably many of us do not actually
realise how close are the links which bind us to our brilliant star as
he carries us along with him through space. It is only when an unusual
outburst occurs, such as I have just described, that we feel how every
thrill which passes through our atmosphere, through the life-current of
every plant, and through the fibre and nerve of every animal has some
relation to the huge source of light, heat, electricity, and magnetism
at which we are now gazing across a space of more than 93,000,000 miles.
Yet it is well to remember that the sudden storm and the violent
eruption are the exceptional occurrences, and that their use to us as
students is chiefly to lead us to understand the steady and constant
thrill which, never ceasing, never faltering, fulfils the great purpose
of the unseen Lawgiver in sustaining all movement and life in our little
world.
CHAPTER VII
AN EVENING AMONG THE STARS
[Illustration]
"Do you love the stars?" asked the magician of his lads, as they crowded
round him on the college green, one evening in March, to look through
his portable telescope.
"Have you ever sat at the window on a clear frosty night, or in the
garden in summer, and looked up at those wondrous lights in the sky,
pondering what they are, and what purpose they serve?"
I will confess to you that when I lived in London I did not think much
about the stars, for in the streets very few can be seen at a time even
on a clear night; and during the long evenings in summer, when town
people visit the country, you must stay up late to see a brilliant
display of starlight. It is when driving or walking across country on a
winter's evening week after week, and looking all round the sky, that
the glorious suns of heaven force you to take notice of them; and Orion
becomes a companion with his seven brilliant stars and his magnificent
nebula, which appears as a small pale blue patch, to eyes accustomed to
look for it, when the night is very bright and clear. It is then that
Charles's Wain becomes quite a study in all its different positions, its
horses now careering upwards, now plunging downwards, while the waggon,
whether upwards or downwards, points ever true, by the two stars of its
tail-board, to the steadfast pole-star.
It is on such nights as these that, looking southward from Orion, we
recognise the dog-star Sirius, bright long before other stars have
conquered the twilight, and feast our eye upon his glorious white beams;
and then, turning northwards, are startled by the soft lustrous sheen of
Vega just appearing above the horizon.
But stop, I must remember that I have not yet introduced you to these
groups of stars; and moreover that, though we shall find them now in the
positions I mention, yet if you look for them a few hours later
to-night, or at the same hour later in the year, you will not find them
in the same places in the sky. For as our earth turns daily on its axis,
the stars _appear_ to alter their position hour by hour, and in the same
way as we travel yearly on our journey round the sun, they _appear_ to
move in the sky month by month. Yet with a little practice it is easy to
recognise the principal stars, for, as it is our movement and not theirs
which makes us see them in different parts of the sky, they always
remain in the same position with regard to each other. In a very short
time, with the help of such a book as Proctor's _Star Atlas_; you could
pick out all the chief constellations and most conspicuous stars for
yourselves.
One of the best ways is to take note of the stars each night as they
creep out one by one after sunset. If you take your place at the window
to-morrow night as the twilight fades away, you will see them gradually
appear, now in one part, now in another of the sky, as
"One by one each little star
Sits on its golden throne."
The first to appear will be Sirius or the dog-star (see Fig. 54), that
pure white star which you can observe now rather low down to the south,
and which belongs to the constellation _Canis Major_. As Sirius is one
of the most brilliant stars in the sky, he can be seen very soon after
the sun is gone at this time of year. If, however, you had any doubt as
to what star he was, you would not doubt long, for in a little while two
beautiful stars start into view above him more to the west, and between
them three smaller ones in a close row, forming the cross in the
constellation of Orion, which is always very easy to recognise. Now the
three stars of Orion's belt which make the short piece of the cross
always point to Sirius, while Betelgeux in his right shoulder, and Rigel
in his left foot (see Figs. 54 and 55), complete the long piece, and
these all show very early in the twilight. You would have to wait longer
for the other two leading stars, Bellatrix in the right shoulder and
[Greek: k] Orionis in the right leg, for these stars are feebler and
only seen when the light has faded quite away.
[Illustration: Fig. 54.
Some of the constellations seen when looking south in March from six to
nine o'clock.]
By that time you would see that there are an immense number of stars in
Orion visible even to the naked eye, besides the veil of misty, tiny
stars called the "Milky Way" which passes over his arm and club. Yet the
figure of the huntsman is very difficult to trace, and the seven bright
stars, the five of the cross and those in the left arm and knee, are all
you need remember.
No! not altogether all, for on a bright clear night like this you can
detect a faint greenish blue patch (N, Fig. 54) just below the belt, and
having a bright star in the centre. This is called the "Great Nebula" or
mist of Orion (see Frontispiece). With your telescopes it looks very
small indeed, for only the central and brightest part is seen. Really,
however, it is so widespread that our whole solar system is as nothing
compared to it. But even your telescopes will show, somewhere near the
centre, what appears to be a bright and very beautiful star (see Fig.
55) surrounded by a darker space than the rest of the nebula, while in
my telescope you will see many stars scattered over the mist.
[Illustration: Fig. 55.
Chief stars of Orion, with Aldebaran. (After Proctor.)]
Now first let me tell you that these last stars do not, so far as we
know, lie _in_ the nebula, but are scattered about in the heavens
between us and it, perhaps millions of miles nearer our earth. But with
the bright star in the centre it is different, for the spectroscope
tells us that the mist passes _over_ it, so that it is either behind or
in the nebula. Moreover, this star is very interesting, for it is not
really one star, but six arranged in a group (see Fig. 56). You can see
four distinctly through my telescope, forming a trapezium or four-sided
figure, and more powerful instruments show two smaller ones. So [Greek:
th] Orionis, or the Trapezium of Orion, is a multiple star, probably
lying in the midst of the nebula.
[Illustration: Fig. 56.
The trapezium, [Greek: th] Orionis, in the nebula of Orion. (Herschel.)]
The next question is, What is the mist itself composed of? For a long
time telescopes could give us no answer. At last one night Lord Rosse,
looking through his giant telescope at the densest part of the nebula,
saw myriads of minute stars which had never been seen before. "Then,"
you will say, "it is after all only a cluster of stars too small for our
telescopes to distinguish." Wait a bit; it is always dangerous to draw
hasty conclusions from single observations. What Lord Rosse said was
true as to that particular part of the nebula, but not the whole truth
even there, and not at all true of other parts, as the spectroscope
tells us.
For though the light of nebulæ, or luminous mists, is so faint that a
spectrum can only be got by most delicate operations, yet Dr. Huggins
has succeeded in examining several. Among these is the nebula of Orion,
and we now know that when the light of the mist is spread out it gives,
not a continuous band of colour such as would be given by stars, but
_faint coloured lines_ on a dark ground (see Fig. 57). Such lines as
these we have already learnt are always given by gases, and the
particular bright lines thrown by Orion's nebula answer to those given
by nitrogen and hydrogen, and some other unknown gases. So we learn at
last that the true mist of the nebula is formed of glowing gas, while
parts have probably a great number of minute stars in them.
[Illustration: Fig. 57.
Nebula-spectrum.
Sun-spectrum.
Spectrum of Orion's Nebula, showing bright lines, with sun-spectrum
below for comparison.]
Till within a very short time ago only those people who had access to
very powerful telescopes could see the real appearance of Orion, for
drawings made of it were necessarily very imperfect; but now that
telescopes have been made expressly for carrying photographic
appliances, even these faint mists print their own image for us. In 1880
Professor Draper of America photographed the nebula of Orion, in March
1881 Mr. Common got a still better effect, and last year Mr. Isaac
Roberts succeeded in taking the most perfect and beautiful photograph[1]
yet obtained, in which the true beauty of this wonderful mist stands out
clearly. I have marked on the edge of our copy two points [Greek: th]
and [Greek: th]´, and if you follow out straight lines from these points
till they meet, you will arrive at the spot where the multiple star
lies. It cannot, however, be seen here, because the plate was exposed
for three hours and a half, and after a time the mist prints itself so
densely as to smother the light of the stars. Look well at this
photograph when you go indoors and fix it on your memory, and then on
clear nights accustom your eye to find the nebula below the three stars
of the belt, for it tells a wonderful story.
[1] Reproduced in the Frontispiece with Mr. Roberts's kind permission.
The star-halo at the top of the plate is caused by diffraction of
light in the telescope, and comes only from an ordinary star.
More than a hundred years ago the great German philosopher Kant
suggested that our sun, our earth, and all the heavenly bodies might
have begun as gases, and the astronomer Laplace taught this as the most
likely history of their formation. After a few years, however, when
powerful telescopes showed that many of the nebulæ were only clusters of
very minute stars, astronomers thought that Laplace's teaching had been
wrong. But now the spectroscope has revealed to us glowing gas actually
filling large spaces in the sky, and every year accurate observations
and experiments tell us more and more about these marvellous distant
mists. Some day, though perhaps not while you or I are here to know it,
Orion's nebula, with its glowing gas and minute star-dust, may give some
clue to the early history of the heavenly bodies; and for this reason I
wish you to recognise and ponder over it, as I have often done, when it
shines down on the rugged moor in the stillness of a clear frosty
winter's night.
But we must pass on for, while I have been talking, the whole sky has
become bespangled with hundreds of stars. That glorious one to the west,
which you can find by following (Fig. 54) a curved line upwards from
Betelgeux, is the beautiful red star Aldebaran or the hindmost; so
called by the Arabs, because he drives before him that well-known
cluster, the Pleiades, which we reach by continuing the curve westwards
and upwards. Stop to look at this cluster through your telescopes, for
it will delight you; even with the naked eye you can count from six to
ten stars in it, and an opera-glass will show about thirty, though they
are so scattered you will have to move the glass about to find them. Yet
though my telescope shows a great many more, you cannot even count all
the chief ones through it, for in powerful telescopes more than 600
stars have been seen in the single cluster! while a photograph taken by
Mr. Roberts shows also four lovely patches of nebula.
And now from the Pleiades let us pass on directly overhead to the
beautiful star Capella, which once was red but now is blue, and drop
down gently to the south-east, where Castor and Pollux, the two most
prominent stars in the constellation "Gemini" or the twins, show
brilliantly against the black sky. Pause here a moment, for I want to
tell you something about Castor, the one nearest to Capella. If you look
at Castor through your telescopes, some of you may possibly guess that
it is really two stars, but you will have to look through mine to see it
clearly. These two stars have been watched carefully for many years, and
there is now no doubt that one of them is moving slowly round the other.
Such stars as these are called "binary," to distinguish them from stars
that merely _appear_ double because they stand nearly in a line one
behind the other in the heavens, although they may be millions of miles
apart. But "binary" stars are actually moving in one system, and revolve
round each other as our earth moves round the sun.
I wonder if it strikes you what a grand discovery this is? You will
remember that it is gravitation which keeps the moon held to the earth
so that it moves round in a circle, and which keeps the earth and other
planets moving round the sun. But till these binary stars were
discovered we had no means of guessing that this law had any force
beyond our own solar system. Now, however, we learn that the same law
and order which reigns in our small group of planets is in action
billions of miles away among distant suns, so that they are held
together and move round each other as our earth moves round our sun. I
will repeat to you what Sir R. Ball, the Astronomer-Royal of Ireland,
says about this, for his words have remained in my mind ever since I
read them, and I should like them to linger in yours till you are old
enough to feel their force and grandeur. "This discovery," he writes,
"gave us knowledge we could have gained from no other source. From the
binary stars came a whisper across the vast abyss of space. That whisper
told us that the law of gravitation is not peculiar to the solar system.
It gives us grounds for believing that it is obeyed throughout the
length, the breadth, the depth, and the height of the entire
universe."[1]
[1] _The Story of the Heavens._
And now, leaving Castor and going round to the east, we pass through the
constellation Leo or the Lion, and I want you particularly to notice six
stars in the shape of a sickle, which form the front part of the lion,
the brightest, called Regulus, being the end of the handle.[1] This
sickle is very interesting, because it marks the part of the heavens
from which the brilliant shower of November meteors radiates once in
thirty-three years. This is, however, too long a story to be told
to-night, so we will pass through Leo, and turning northwards, look high
up in the north-east (Fig. 58), where "Charles's Wain" stretches far
across the sky. I need not point this out to you, for every country lad
knows and delights in it. You could not have seen it in the twilight
when Sirius first shone out, for these stars are not so powerful as he
is. But they come out very soon after him, and when once fairly bright,
the four stars which form the waggon, wider at the top than at the
bottom, can never be mistaken, and the three stars in front, the last
bending below the others, are just in the right position for the horses.
For this reason I prefer the country people's name of Charles's Wain or
Waggon to that of the "Plough," which astronomers generally give to
these seven stars. They really form part of an enormous constellation
called the "Great Bear" (Fig. 59), but, as in the case of Orion, it is
very difficult to make out the whole of Bruin in the sky.
[1] In Fig. 54 the sickle alone comes within the picture.
[Illustration: Fig. 58.
Some of the constellations seen when looking north in March from six to
nine o'clock.]
[Illustration: Fig. 59.
The Great Bear, showing the position of Charles's Wain, and also the
small binary star [Greek: x] in the hind foot, whose period has been
determined.]
Now, although most people know Charles's Wain when they see it, we may
still learn a good deal about it. Look carefully at the second star from
the waggon and you will see another star close to it, called by country
people "Jack by the second horse," and by astronomers "Alcor." Even in
your small telescopes you can see that Jack or Alcor is not so close as
he appears to the naked eye, but a long way off from the horse, while in
my telescope you will find this second horse (called Mizar) split up
into two stars, one a brilliant white and the other a pale emerald
green. We do not know whether these two form a binary, for they have not
yet been observed to move round each other.
Take care in looking that you do not confuse the stars one with another,
for you must remember that your telescope makes objects appear upside
down, and Alcor will therefore appear in it _below_ the two stars
forming the horse.
But though we do not know whether Mizar is binary, there is a little
star a long way below the waggon, in the left hind paw of the Great Bear
([Greek: x], Figs. 58 and 59), which has taught us a great deal, for it
is composed of two stars, one white and the other grey, which move right
round each other once in sixty years, so that astronomers have observed
more than one revolution since powerful telescopes were invented. You
will have to look in my telescope to see the two stars divided, but you
can make an interesting observation for yourselves by comparing the
light of this binary star with the light of Castor, for Castor is such
an immense distance from us that his light takes more than a hundred
years to reach us, while the light of this smaller star comes in
sixty-one years, yet see how incomparably brighter Castor is of the two.
This proves that brilliant stars are not always the nearest, but that a
near star may be small and faint and a far-off one large and bright.
[Illustration: Fig. 60.
The seven stars of Charles's Wain, showing the directions in which they
are travelling. (After Proctor.)]
There is another very interesting fact known to us about Charles's Wain
which I should like you to remember when you look at it. This is that
the seven stars are travelling onwards in the sky, and not all in the
same direction. It was already suspected centuries ago that, besides the
_apparent_ motion of all the stars in the heavens caused by our own
movements, they have each also a _real_ motion and are travelling in
space, though they are so inconceivably far off that we do not notice
it. It has now been proved, by very accurate observations with powerful
instruments, that three of the stars forming the waggon and the two
horses nearest to it, together with Jack, are drifting forwards (see
Fig. 60), while the top star of the tailboard of the waggon and the
leader of the horses are drifting the other way. Thus, thousands of
years hence Charles's Wain will most likely have quite altered its
shape, though so very slowly that each generation will think it is
unchanged.
One more experiment with Charles's Wain, before we leave it, will help
you to imagine the endless millions of stars which fill the universe.
Look up at the waggon and try to count how many stars you can see inside
it with the naked eye. You may, if your eye is keen, be able to count
twelve. Now take an opera-glass and the twelve become two hundred. With
your telescopes they will increase again in number. In my telescope
upstairs the two hundred become hundreds, while in one of the giant
telescopes, such as Lord Rosse's in Ireland, or the great telescope at
Washington in the United States, thousands of stars are brought into
view within that four-sided space!
Now this part of the sky is not fuller of stars than many others; yet at
first, looking up as any one might on a clear evening, we thought only
twelve were there. Cast your eyes all round the heavens. On a clear
night like this you may perhaps, with the naked eye, have in view about
3000 stars; then consider that a powerful telescope can multiply these
by thousands upon thousands, so that we can reckon about 20,000,000
where you see only 3000. If you add to these the stars that rise later
at night, and those of the southern hemisphere which never rise in our
latitude, you would have in all about 50,000,000 stars, which we are
able to see from our tiny world through our most powerful telescopes.
But we can go farther yet. When our telescopes fail, we turn to our
other magic seer, the photographic camera, and trapping rays of light
from stars invisible in the most powerful telescope, make them print
their image on the photographic plate, and at once our numbers are so
enormously increased that if we could photograph the whole of the
heavens as visible from our earth, we should have impressions of at
least 170,000,000 stars!
These numbers are so difficult to grasp that we had better pass on to
something easier, and our next step brings us to the one star in the
heavens which never appears to move, as our world turns. To find it we
have only to draw a line upwards through the two stars in the tailboard
of the waggon and on into space. Indeed these two stars are called "the
Pointers," because a line prolonged onwards from them will, with a very
slight curve, bring us to the "Pole-star" (see Fig. 58). This star,
though not one of the largest, is important, because it is very near
that spot in the sky towards which the North Pole of our earth points.
The consequence is, that though all the other stars appear to move in a
circle round the heavens, and to be in different places at different
seasons, this star remains always in the same place, only appearing to
describe a very tiny circle in the sky round the exact spot to which our
North Pole points.
Month after month and year after year it shines exactly over that
thatched cottage yonder, which you see now immediately below it; and
wherever you are in the northern hemisphere, if you once note a certain
tree, or chimney, or steeple which points upwards to the Pole-star, it
will guide you to it at any hour on any night of the year, though the
other constellations will be now on one side, now on the other side of
it.
The Pole-star is really the front horse of a small imitation of
Charles's Wain, which, however, has never been called by any special
name, but only part of the "Little Bear." Those two hind stars of the
tiny waggon, which are so much the brightest, are called the "Guards,"
because they appear to move in a circle round the Pole-star night after
night and year after year like sentries.
[Illustration: Fig. 61.
The constellation of Cassiopeia, and the heavenly bodies which can be
found by means of it.[1]]
[1] For Almach see Fig. 58, it has been accidentally omitted from this
figure.
Opposite to them, on the farther side of the Pole-star, is a well-marked
constellation, a widespread W written in the sky by five large stars;
the second V of the W has rather a longer point than the first, and as
we see it now the letter is almost upside down (see Fig. 58).
These are the five brightest stars in the constellation Cassiopeia, with
a sixth not quite so bright in the third stroke of the W. You can never
miss them when you have once seen them, even though they lie in the
midst of a dense layer of the stars of the Milky Way, and if you have
any difficulty at first, you have only to look as far on the one side of
the Pole-star as the top hind star of Charles's Wain is on the other,
and you must find them. I want to use them to-night chiefly as guides to
find two remarkable objects which I hope you will look at again and
again. The first is a small round misty patch not easy to see, but which
you will find by following out the _second_ stroke of the first V of the
W. Beginning at the top, and following the line to the point of the V,
continue on across the sky, and then search with your telescope till you
catch a glimpse of this faint mist (_c_, Fig. 58; star-cluster, Fig.
61). You will see at once that it is sparkling all over with stars, for
in fact you have actually before you in that tiny cluster more stars
than you can see with the naked eye all over the heavens! Think for a
moment what this means. One faint misty spot in the constellation
Perseus, which we should have passed over unheeded without a telescope,
proves to be a group of more than 3000 suns!
The second object you will find more easily, for it is larger and
brighter, and appears as a faint dull spot to the naked eye. Going back
to Cassiopeia, follow out the _second_ V in the W from the top to the
point of the V and onwards till your eye rests upon this misty cloud,
which is called the Great Nebula of Andromeda, and has sometimes been
mistaken for a comet (Figs. 58 and 61). You will, however, be
disappointed when you look through the telescope, for it will still only
appear a mist, and you will be able to make nothing of it, except that
instead of being of an irregular shape like Orion, it is elliptical; and
in a powerful telescope two dark rifts can be seen separating the
streams of nebulous matter. These rifts are now shown in a photograph
taken by Mr. Roberts, 1st October 1888, to be two vast dusky rings lying
between the spiral stream of light, which winds in an ellipse till it
ends in a small nucleus at the centre.
Ah! you will say, this must be a cloud of gas like Orion's nebula, only
winding round and round. No! the spectroscope steps in here and tells us
that the light shows something very much like a continuous spectrum, but
not as long as it ought to be at the red end. Now, since gases give only
bright lines, this nebula cannot be entirely gaseous. Then it must be
made of stars too far off to see? If so, it is very strange that though
it is so dense and bright in some parts, and so spread out and clear in
others, the most powerful telescopes cannot break it up into stars. In
fact, the composition of the great nebula of Andromeda is still a
mystery, and remains for one of you boys to study when he has become a
great astronomer.
Still one more strange star we will notice before we leave this part of
the heavens. You will find it, or at least go very near it, by
continuing northwards the line you drew from Cassiopeia to the Star
Cluster (_c_, Fig. 58), and as it is a bright star, you will not miss
it. That is to say, it is bright to-night and will remain so till
to-morrow night, but if you come to me about nine o'clock to-morrow
evening I will show you that it is growing dim, and if we had patience
to watch through the night we should find, three or four hours later
still, that it looks like one of the smaller stars. Then it will begin
to brighten again, and in four hours more will be as bright as at first.
It will remain so for nearly three days, or, to speak accurately, 2
days, 20 hours, 48 minutes, and 55 seconds, and then will begin to grow
dull again. This star is called Algol the Variable. There are several
such stars in the heavens, and we do not know why they vary, unless
perhaps some dark globe passes round them, cutting off part of their
light for a time.
And now, if your eyes are not weary, let us go back to the Pole-star and
draw a line from it straight down the horizon due north. Shortly before
we arrive there you will see a very brilliant bluish-white star a little
to the east of this line. This is Vega, one of the brightest stars in
the heavens except Sirius. It had not risen in the earlier part of the
evening, but now it is well up and will appear to go on, steadily
mounting as it circles round the Pole-star, till at four o'clock
to-morrow morning it will be right overhead towards the south.
But beautiful as Vega is, a still more interesting star lies close to it
(see Fig. 58). This small star, called [Greek: e] Lyræ by astronomers,
looks a little longer in one direction than in the other, and even with
the naked eye some people can see a division in the middle dividing it
into two stars. Your telescopes will show them easily, and a powerful
telescope tells a wonderful story, for it reveals that each of these two
stars is again composed of two stars, so that [Greek: e] Lyræ (Fig. 62)
is really a double-double star. There is no doubt that each pair is a
binary star, that is, the two stars move round each other very slowly,
and possibly both pairs may also revolve round a common centre. There
are at least 10,000 double stars in the heavens; though, as we have
seen, they are not all binary. The list of binary stars, however,
increases every year as they are carefully examined, and probably about
one star in three over the whole sky is made up of more than one sun.
[Illustration: Fig. 62.
[Greek: e] Lyræ. A double-binary star. Each couple revolves, and the
couples probably also revolve round each other. (After Chambers.)]
Let us turn the telescope for a short time upon a few of the double
stars and we shall have a great treat, for one of the most interesting
facts about them is that both stars are rarely of the same colour. It
seems strange at first to speak of stars as coloured, but they do not by
any means all give out the same kind of light. Our sun is yellow, and so
are the Pole-star and Pollux; but Sirius, Vega, and Regulus are
dazzling white or bluish-white, Arcturus is a yellowish-white,
Aldebaran is a bright yellow-red, Betelgeux a deep orange-red, as you
may see now in the telescope, for he is full in view; while Antares, a
star in the constellation of the Scorpion, which at this time of year
cannot be seen till four in the morning, is an intense ruby red.
[Illustration: _Plate II._]
COLOURED DOUBLE STARS.
[Illustration: [Greek: g] _Andromedæ_.]
[Illustration: [Greek: e] _Boötis_.]
[Illustration: [Greek: d] _Geminorum_.]
[Illustration: [Greek: a] _Herculis_.]
[Illustration: [Greek: b] _Cygni_.]
[Illustration: [Greek: ê] _Cassiopeiæ_.]
It appears to be almost a rule with double stars to be of two colours.
Look up at Almach ([Greek: g] Andromedæ), a bright star standing next to
Algol the Variable in the sweep of four bright stars behind Cassiopeia
(see Fig. 58). Even to the naked eye he appears to flash in a strange
way, and in the telescope he appears as two lovely stars, one a deep
orange and the other a pale green, while in powerful telescopes the
green one splits again into two (Plate II.) Then again, [Greek: ê]
Cassiopeæ, the sixth star lying between the two large ones in the second
V of Cassiopeia, divides into a yellow star and a small rich purple one,
and [Greek: d] Geminorum, a bright star not far from Pollux in the
constellation Gemini, is composed of a large green star and a small
purple one. Another very famous double star ([Greek: b] Cygni), which
rises only a little later in the evening, lies below Vega a little to
the left. It is composed of two lovely stars; one an orange yellow and
the other blue; while [Greek: e] Boötis, just visible above the horizon,
is composed of a large yellow star and a very small green one.[1]
[1] The plate of coloured stars has been most kindly drawn to scale
and coloured for me by Mr. Arthur Cottam, F.R.A.S.
There are many other stars of two colours even among the few
constellations we have picked out to-night, as, for example, the star
at the top of the tailboard of Charles's Waggon and the second horse
Mizar. Rigel in Orion, and the two outer stars of the belt, [Greek: a]
Herculis, which will rise later in the evening, and the beautiful triple
star ([Greek: z] Cancer) near the Beehive (see Fig. 54), are all
composed of two or more stars of different colours.
Why do these suns give out such beautiful coloured light? The telescope
cannot tell us, but the spectroscope again reveals the secrets so long
hidden from us. By a series of very delicate experiments, Dr. Huggins
has shown that the light of all stars is sifted before it comes to us,
just as the light of our sun is; and those rays which are least cut off
play most strongly on our eyes, and give the colour to the star. The
question is a difficult one but I will try to give you some idea of it,
that you may form some picture in your mind of what happens.
We learnt in our last lecture (p. 131) that the light from our sun
passes through the great atmosphere of vapours surrounding him before it
goes out into space, and that many rays are in this way cut off; so that
when we spread out his light in a long spectrum there are dark lines or
spaces where no light falls.[1] Now in sunlight these dark lines are
scattered pretty evenly over the spectrum, so that about as much light
is cut off in one part as in another, and no one colour is stronger than
the rest.
[1] See No. 1 in Table of Spectra, Plate I.
Dr. Huggins found, however, that in coloured stars the dark spaces are
often crowded into particular parts of the long band of colour forming
the spectrum; showing that many of those light-rays have been cut off
in the atmosphere round the star, and thus their particular colours are
dimmed, leaving the other colour or colours more vivid. In red stars,
for example, the yellow, blue, and green parts of the spectrum are much
lined while the red end is strong and clear. With blue stars it is just
the opposite, and the violet end is most free from dark lines. So there
are really brilliantly coloured suns shining in the heavens, and in many
cases two or more of these revolve round each other.
And now I have kept your attention and strained your eyes long enough,
and you have objects to study for many a long evening before you will
learn to see them plainly. You must not expect to find them every night,
for the lightest cloud or the faintest moonlight will hide many of them
from view; and, moreover, though you may learn to use the telescope
fairly, you will often not know how to get a clear view with it. Still,
you may learn a great deal, and before we go in I want to put a thought
into your minds which will make astronomy still more interesting. We
have seen that the stronger our telescopes the more stars,
star-clusters, and nebulæ we see, and we cannot doubt that there are
still countless heavenly bodies quite unknown to us. Some years ago
Bessel the astronomer found that Sirius, in its real motion through the
heavens, moves irregularly, travelling sometimes a little more slowly
than at other times, and he suggested that some unseen companion must be
pulling at him.
Twenty-eight years later, in 1862, two celebrated opticians, father and
son, both named Alvan Clark, were trying a new telescope at Chicago
University, when suddenly the son, who was looking at Sirius, exclaimed,
"Why, father, the star has a companion!" And so it was. The powerful
telescope showed what Bessel had foretold, and proved Sirius to be a
"binary" star--that is, as we have seen, a star which has another moving
round it.
It has since been proved that this companion is twenty-eight times
farther from Sirius than we are from our sun, and moves round him in
about forty-nine years. It is seven times as heavy as our sun, and yet
gives out so little light that only the keenest telescopes can bring it
into view.
Now if such a large body as this can give so very faint a light that we
can scarcely see it, though Sirius, which is close to it, shines
brightest of any star in the heavens, how many more bodies must there be
which we shall never see, even among those which give out light, while
how many there are dark like our earth, who can tell?
Now that we know each of the stars to be a brilliant sun, many of them
far, far brighter than ours, yet so like in their nature and laws, we
can scarcely help speculating whether round these glorious suns, worlds
of some kind may not be moving. If so, and there are people in them,
what a strange effect those double coloured suns must produce with red
daylight one day and blue daylight another!
Surely, as we look up at the myriads of stars bespangling the sky, and
remember that our star-sun has seven planets moving round it of which
one at least--our own earth--is full of living beings, we must picture
these glorious suns as the centres of unseen systems, so that those
twinkling specks become as suggestive as the faint lights of a great
fleet far out at sea, which tell us of mighty ships, together with
frigates and gunboats, full of living beings, though we cannot see them,
nor even guess what they may be like. How insignificant we feel when we
look upon that starlit sky and remember that the whole of our solar
system would be but a tiny speck of light if seen as far off as we see
the stars! If our little earth and our short life upon it were all we
could boast of we should be mites indeed.
But our very study to-night lifts us above these and reminds us that
there is a spirit within us which even now can travel beyond the narrow
bounds of our globe, measure the vast distances between us and the
stars, gauge their brightness, estimate their weight, and discern their
movements. As we gaze into the depths of the starlit sky, and travel
onwards and onwards in imagination to those distant stars which
photography alone reveals to us, do not our hearts leap at the thought
of a day which must surely come when, fettered and bound no longer to
earth, this spirit shall wander forth and penetrate some of the mystery
of those mighty suns at which we now gaze in silent awe.
CHAPTER VIII
LITTLE BEINGS FROM A MINIATURE OCEAN
[Illustration]
In our last lecture we soared far away into boundless space, and lost
ourselves for a time among seen and unseen suns. In this lecture we will
come back not merely to our little world, nor even to one of the
widespread oceans which cover so much of it, but to one single pool
lying just above the limits of low tide, so that it is only uncovered
for a very short time every day. This pool is to be found in a secluded
bay within an hour's journey by train from this college, and only a few
miles from Torquay. It has no name, so far as I know, nor do many people
visit it, otherwise I should not have kept my little pool so long
undisturbed. As it is, however, for many years past I have had only to
make sure as to the time of low tide, and put myself in the train; and
then, unless the sea was very rough and stormy, I could examine the
little inhabitants of my miniature ocean in peace.
The pool lies in a deep hollow among a group of rocks and boulders,
close to the entrance of the cove, which can only be entered at low
water; it does not measure more than two feet across, so that you can
step over it, if you take care not to slip on the masses of green and
brown seaweed growing over the rocks on its sides, as I have done many a
time when collecting specimens for our salt-water aquarium. I find now
the only way is to lie flat down on the rock, so that my hands and eyes
are free to observe and handle, and then, bringing my eye down to the
edge of the pool, to lift the seaweeds and let the sunlight enter into
the chinks and crannies. In this way I can catch sight of many a small
being either on the seaweed or the rocky ledges, and even creatures
transparent as glass become visible by the thin outline gleaming in the
sunlight. Then I pluck a piece of seaweed, or chip off a fragment of
rock with a sharp-edged collecting knife, bringing away the specimen
uninjured upon it, and place it carefully in its own separate bottle to
be carried home alive and well.
Now though this little pool and I are old friends, I find new treasures
in it almost every time I go, for it is almost as full of living things
as the heavens are of stars, and the tide as it comes and goes brings
many a mother there to find a safe home for her little ones, and many a
waif and stray to seek shelter from the troublous life of the open
ocean.
You will perhaps find it difficult to believe that in this rock-bound
basin there can be millions of living creatures hidden away among the
fine feathery weeds; yet so it is. Not that they are always the same. At
one time it may be the home of myriads of infant crabs, not an eighth of
an inch long, at another of baby sea-urchins only visible to the naked
eye as minute spots in the water, at another of young jelly-fish growing
on their tiny stalks, and splitting off one by one as transparent bells
to float away with the rising tide. Or it may be that the whelk has
chosen this quiet nook to deposit her leathery eggs; or young barnacles,
periwinkles, and limpets are growing up among the green and brown
tangles, while the far-sailing velella and the stay-at-home sea-squirts,
together with a variety of other sea-animals, find a nursery and shelter
in their youth in this quiet harbour of rest.
And besides these casual visitors there are numberless creatures which
have lived and multiplied there, ever since I first visited the pool.
Tender red, olive-coloured, and green seaweeds, stony corallines, and
acorn-barnacles lining the floor, sea-anemones clinging to the sides,
sponges tiny and many-coloured hiding under the ledges, and limpets and
mussels wedged in the cracks. These can be easily seen with the naked
eye, but they are not the most numerous inhabitants; for these we must
search with a magnifying-glass, which will reveal to us wonderful
fairy-forms, delicate crystal vases with tiny creatures in them whose
transparent lashes make whirlpools in the water, living crystal bells so
tiny that whole branches of them look only like a fringe of hair, jelly
globes rising and falling in the water, patches of living jelly
clinging to the rocky sides of the pool, and a hundred other forms, some
so minute that you must examine the fine sand in which they lie under a
powerful microscope before you can even guess that they are there.
[Illustration: Fig. 63.
Group of seaweeds (natural size).
1, _Ulva Linza._ 2, _Sphacelaria filicina._ 3, _Polysiphonia urceolata._
4, _Corallina officinalis._]
So it has proved a rich hunting-ground, where summer and winter, spring
and autumn, I find some form to put under my magic glass. There I can
watch it for weeks growing and multiplying under my care; moved only
from the aquarium, where I keep it supplied with healthy sea-water, to
the tiny transparent trough in which I place it for a few hours to see
the changes it has undergone. I could tell you endless tales of
transformations in these tiny lives, but I want to-day to show you a
few of my friends, most of which I brought yesterday fresh from the
pool, and have prepared for you to examine.
[Illustration: Fig. 64.
_Ulva lactuca_, a green seaweed, greatly magnified to show structure.
(After Oersted.)
_s_, Spores in the cells. _ss_, Spores swimming out. _h_, Holes through
which spores have escaped.]
Let us begin with seaweeds. I have said that there are three leading
colours in my pool--green, olive, and red--and these tints mark roughly
three kinds of weed, though they occur in an endless variety of shapes.
Here is a piece of the beautiful pale green seaweed, called the Laver or
Sea-lettuce, _Ulva Linza_ (1, Fig. 63), which grows in long ribbons in a
sunny nook in the water. I have placed under the first microscope a
piece of this weed which is just sending out young seaweeds in the shape
of tiny cells, with lashes very like those we saw coming from the
moss-flower, and I have pressed them in the position in which they would
naturally leave the plant (_ss_, Fig. 64.).[1] You will also see on this
slide several cells in which these tiny spores _s_ are forming, ready to
burst out and swim; for this green weed is merely a collection of cells,
like the single-celled plants on land. Each cell can work as a separate
plant; it feeds, grows, and can send out its own young spores.
[1] The slice given in Fig. 64 is from a broader-leaved form,
_U. lactuca_, because this species, being composed of only one
layer of cells, is better seen. _Ulva linza_ is composed of two
layers of cells.
This deep olive-green feathery weed (2, Fig. 63), of which a piece is
magnified under the next microscope (2, Fig. 65), is very different. It
is a higher plant, and works harder for its living, using the darker
rays of sunlight which penetrate into shady parts of the pool. So it
comes to pass that its cells divide the work. Those of the feathery
threads make the food, while others, growing on short stalks on the
shafts of the feather make and send out the young spores.
[Illustration: Fig. 65.
Three seaweeds of Fig. 63 much magnified to show fruits. (Harvey.)
2, _Sphacelaria filicina._ 3, _Polysiphonia urceolata._ 4, _Corallina
officinalis._]
Lastly, the lovely red threadlike weeds, such as this _Polysiphonia
urceolata_ (3, Fig. 63), carry actual urns on their stems like those of
mosses. In fact, the history of these urns (see No. 3, Fig. 65) is much
the same in the two classes of plants, only that instead of the urn
being pushed up on a thin stalk as in the moss, it remains on the
seaweed close down to the stem, when it grows out of the plant-egg, and
the tiny plant is shut in till the spores are ready to swim out.
The stony corallines (4, Figs. 63 and 65), which build so much carbonate
of lime into their stems, are near relations of the red seaweeds. There
are plenty of them in my pool. Some of them, of a deep purple colour,
grow upright in stiff groups about three or four inches high; and
others, which form crusts over the stones and weeds, are a pale rose
colour; but both kinds, when the plant dies, leaving the stony skeleton
(1, Fig. 66), are a pure white, and used to be mistaken for corals. They
belong to the same order of plants as the red weeds, which all live in
shady nooks in the pools, and are the highest of their race.
My pool is full of different forms of these four weeds. The green
ribbons float on the surface rooted to the sides of the pool and, as the
sun shines upon it, the glittering bubbles rising from them show that
they are working up food out of the air in the water, and giving off
oxygen. The brown weeds lie chiefly under the shelves of rocks, for they
can manage with less sunlight, and use the darker rays which pass by the
green weeds; and last of all, the red weeds and corallines, small and
delicate in form, line the bottom of the pool in its darkest nooks.
And now if I hand round two specimens--one a coralline, and the other
something you do not yet know--I am sure you will say at first sight
that they belong to the same family, and, in fact, if you buy at the
seaside a group of seaweeds gummed on paper, you will most likely get
both these among them. Yet the truth is, that while the coralline (1,
Fig. 66) is a plant, the other specimen (2) which is called _Sertularia
filicula_, is an animal.
[Illustration: Fig. 66.
Coralline and Sertularia, to show likeness between the animal Sertularia
and the plant Coralline.
1, _Corallina officinalis._ 2, _Sertularia filicula._]
This special sertularian grows upright in my pool on stones or often on
seaweeds, but I have here (Fig. 67) another and much smaller one which
lives literally in millions hanging its cups downwards. I find it not
only under the narrow ledges of the pool sheltered by the seaweed, but
forming a fringe along all the rocks on each side of the cove near to
low-water mark, and for a long time I passed it by thinking it was of no
interest. But I have long since given up thinking this of anything,
especially in my pool, for my magic glass has taught me that there is
not even a living speck which does not open out into something
marvellous and beautiful. So I chipped off a small piece of rock and
brought the fringe home, and found, when I hung it up in clear sea water
as I have done over this glass trough (Fig. 67) and looked at it through
the lens, that each thread of the dense fringe, in itself not a quarter
of an inch deep, turns out to be a tiny sertularian with at least twenty
mouths. You can see this with your pocket lens even as it hangs here,
and when you have examined it you can by and by take off one thread and
put it carefully in the trough. I promise you a sight of the most
beautiful little beings which exist in nature.
[Illustration: Fig. 67.
_Sertularia tenella_, hanging from a splint of rock over a water trough.
Also piece enlarged to show the animal protruding.]
Come and look at it after the lecture. It is a horny branched stem with
a double row of tiny cups all along each side (see Fig. 67). Out of
these cups there appear from time to time sixteen minute transparent
tentacles as fine as spun glass, which wave about in the water. If you
shake the glass a little, in an instant each crystal star vanishes into
its cup, to come out again a few minutes later; so that now here, now
there, the delicate animal-flowers spread out on each side of the stem,
and the tree is covered with moving beings. These tentacles are feelers,
which lash food into a mouth and stomach in each cup, where it is
digested and passed, through a hole in the bottom, along a jelly thread
which runs down the stem and joins all the mouths together. In this way
the food is distributed all over the tree, which is, in fact, one animal
with many feeding-cups. Some day I will show you one of these cups with
the tentacles stretched out and mounted on a slide, so that you can
examine a tentacle with a very strong magnifying power. You will then
see that it is dotted over with cells, in which are coiled fine
threads. The animal uses these threads to paralyse the creatures on
which it feeds, for at the base of each thread there is a poison gland.
In the larger Sertularia (2, Fig. 66) the whole branched tree is
connected by jelly threads running through the stem, and all the
thousands of mouths are spread out in the water. One large form called
the sea-fir _Sertularia cupressina_ grows sometimes three feet high, and
bears as many as a hundred thousand cups, with living mouths, on its
branches.
The next of my minute friends I can only show to the class in a diagram,
but you will see it under the fourth microscope by and by. I had great
trouble in finding it yesterday, though I knew its haunts upon the green
weed, for it is so minute and transparent that even when the weed is in
a trough a magnifying-glass will scarcely detect it. And I must warn you
that if you want to know any of the minute creatures we are studying,
you must visit one place constantly. You may in a casual way find many
of them on seaweed, or in the damp ooze and mud, but it will be by
chance only; to look for them with any certainty you must take trouble
in making their acquaintance.
Turning then to the diagram (Fig. 68) I will describe it as I hope you
will see it under the microscope--a curious tiny, perfectly transparent
open-mouthed vase standing upright on the weed, and having an equally
transparent being rising up in it and waving its tiny lashes in the
water. This is really all one animal, the vase _hc_ being the horny
covering or carapace of the body, which last stands up like a tube in
the centre. If you watch carefully, you may even see the minute atoms of
food twisting round inside the tube until they are digested, after they
have been swept in at the wide open mouth by the whirling lashes. You
will see this more clearly if you put a little rice-flour, very minutely
powdered and coloured by carmine, into the water; for you can trace
these red atoms into some round spaces called _vacuoles_ which are
dotted over the body of the animal, and are really globules of watery
fluid in which the food is probably partly digested.
[Illustration: Fig. 68.
_Thuricolla folliculata_ and _Chilomonas amygdalum_. (Saville Kent.)
1, Thuricolla erect; 2, retracted; 3, dividing. 4, _Chilomonas
amygdalum_. _hc_, Horny carapace. _cv_, Contractile vesicle. _v_,
Closing valves.]
You will notice, however, one round clear space (_cv_) into which they
do not go, and after a time you will be able to observe that this round
spot closes up or contracts very quickly, and then expands again very
slowly. As it expands it fills with a clear fluid, and naturalists have
not yet decided exactly what work it does. It may serve the animal
either for breathing, or as a very simple heart, making the fluids
circulate in the tube. The next interesting point about this little
being is the way it retreats into its sheltering vase. Even while you
are watching, it is quite likely it may all at once draw itself down to
the bottom as in No. 2, and folding down the valves _v_, _v_ of horny
teeth which grow on each side, shut itself in from some fancied danger.
Another very curious point is that, besides sending forth young ones,
these creatures multiply by dividing in two (see No. 3, Fig. 68), each
one closing its own part of the vase into a new home.
There are hundreds of these _Infusoria_, as they are called, in my pond,
some with vases, some without, some fixed to weeds and stones, others
swimming about freely. Even in the water-trough in which this Thuricolla
stands, I saw several smaller forms, and the next microscope has a
trough filled with the minutest form of all, called a Monad (No. 4, Fig.
68). These are so small that 2000 of them would lie side by side in an
inch; that is, if you could make them lie at all, for they are the most
restless little beings, darting hither and thither, scarcely even
halting except to turn back. And yet though there are so many of them,
and as far as we know they have no organs of sight, they never run up
against each other, but glide past more cleverly than any clear-sighted
fish. These creatures are mostly to be found among decaying seaweed, and
though they are so tiny, you can still see distinctly the clear space
(_cv_) contracting and expanding within them.
But if there are so many thousands of mouths to feed, on the tree-like
_Sertulariæ_ as well as in all these _Infusoria_, where does the food
come from?
Partly from the numerous atoms of decaying life all around, and the
minute eggs of animals and spores of plants; but besides these, the pool
is full of minute living plants--small jelly masses with solid coats of
flint which are moulded into most lovely shapes. Plants formed of jelly
and flint! You will think I am joking, but I am not. These plants,
called _Diatoms_, which live both in salt and fresh water, are single
cells feeding and growing just like those we took from the water-butt
(Fig. 29, p. 78), only that instead of a soft covering they build up a
flinty skeleton. They are so small, that many of them must be magnified
to fifty times their real size before you can even see them distinctly.
Yet the skeletons of these almost invisible plants are carved and
chiselled in the most delicate patterns. I showed you a group of these
in our lecture on magic glasses (p. 39), and now I have brought a few
living ones that we may learn to know them. The diagram (Fig. 69) shows
the chief forms you will see on the different slides.
[Illustration: Fig. 69.
Living diatoms.
_a_, _Cocconema lanceolatum_. _b_, _Bacillaria paradoxa_.
_c_, _Gomphonema marinum_. _d_, _Diatoma hyalina_.]
The first one, _Bacillaria paradoxa_ (_b_, Fig. 69), looks like a number
of rods clinging one to another in a string, but each one of these is a
single-celled plant with a jelly cell surrounding the flinty skeleton.
You will see that they move to and fro over each other in the water.
[Illustration: Fig. 70.
A diatom (_Diatoma vulgare_) growing.
_a_, _b_, Flint skeleton inside the jelly-cell. _a_, _c_ and _d_, _b_,
Two flint skeletons formed by new valves, _c_ and _d_, forming within
the first skeleton.]
The next two forms, _a_ and _c_, look much more like plants, for the
cells arrange themselves on a jelly stem, which by and by disappears,
leaving only the separate flint skeletons such as you see in Fig. 16.
The last form, _d_, is something midway between the other forms, the
separate cells hang on to each other and also on to a straight jelly
stem.
Another species of Diatoma (Fig. 70) called _Diatoma vulgare_, is a very
simple and common form, and will help to explain how these plants grow.
The two flinty valves _a_, _b_ inside the cell are not quite the same
size; the older one _a_ is larger than the younger one _b_ and fits over
it like the cover of a pill-box. As the plant grows, the cell enlarges
and forms two more valves, one _c_ fitting into the cover _a_, so as to
make a complete box _ac_, and a second, _d_, back to back with _c_,
fitting into the valve _b_, and making another complete box _bd_. This
goes on very rapidly, and in this plant each new cell separates as it is
formed, and the free diatoms move about quite actively in the water.
If you consider for a moment, you will see that, as the new valves
always fit into the old ones, each must be smaller than the last, and so
there comes a time when the valves have become too small to go on
increasing. Then the plant must begin afresh. So the two halves of the
last cell open, and throwing out their flinty skeletons, cover
themselves with a thin jelly layer, and form a new cell which grows
larger than any of the old ones. These, which are spore-cells, then form
flinty valves inside, and the whole thing begins again.
Now though the plants themselves die, or become the food of minute
animals, the flinty skeletons are not destroyed, but go on accumulating
in the waters of ponds, lakes, rivers, and seas, all over the world.
Untold millions have no doubt crumbled to dust and gone back into the
waters, but untold millions also have survived. The towns of Berlin in
Europe and of Richmond in the United States are actually built upon
ground called "infusorial earth," composed almost entirely of valves of
these minute diatoms which have accumulated to a thickness of more than
eighty feet! Those under Berlin are fresh-water forms, and must have
lived in a lake, while those of Richmond belong to salt-water forms.
Every inch of the ground under those cities represents thousands and
thousands of living plants which flourished in ages long gone by, and
were no larger than those you will see presently under the microscope.
These are a very few of the microscopic inhabitants of my pond, but, as
you will confuse them if I show you too many, we will conclude with two
rather larger specimens, and examine them carefully. The first, called
the Cydippe, is a lovely, transparent living ball, which I want to
explain to you because it is so wondrously beautiful. The second, the
Sea-mat or Flustra, looks like a crumpled drab-coloured seaweed, but is
really composed of many thousands of grottos, the homes of tiny
sea-animals.
[Illustration: Fig. 71.
_Cydippe Pileus._
1, Animal with tentacles _t_, bearing small tendrils _t´_. 2, Body of
animal enlarged. _m_, Mouth. _c_, Digestive cavity. _s_, Sac into which
the tentacles are withdrawn. _p_, Bands with comb-like plates. 3,
Portion of a band enlarged to show the moving plates _p_.]
Let us take the Cydippe first (1, Fig. 71). I have six here, each in a
separate tumbler, and could have brought many more, for when I dipped my
net in the pool yesterday such numbers were caught in it that I believe
the retreating tide must just have left a shoal behind. Put a tumbler on
the desk in front of you, and if the light falls well upon it you will
see a transparent ball about the size of a large pea marked with eight
bright bands, which begin at the lower end of the ball and reach nearly
to the top, dividing the outside into sections like the ribs of a melon.
The creature is so perfectly transparent that you can count all the
eight bands.
At the top of the ball is a slight bulge which is the mouth (_m_ 2, Fig.
71), and from it, inside the ball, hangs a long bag or stomach, which
opens below into a cavity c, from which two canals branch out, one on
each side, and these divide again into four canals which go one into
each of the tubes running down the bands. From this cavity the food,
which is digested in the stomach, is carried by the canals all over the
body. The smaller tubes which branch out of these canals cannot be seen
clearly without a very strong lens, and the only other parts you can
discern in this transparent ball are two long sacs on each side of the
lower end. These are the tentacle sacs, in which are coiled up the
tentacles, which we shall describe presently. Lastly, you can notice
that the bands outside the globe are broader in the middle than at the
ends, and are striped across by a number of ridges.
In moving the tumblers the water has naturally been shaken, and the
creature being alarmed will probably at first remain motionless. But
very soon it will begin to play in the water, rising and falling, and
swimming gracefully from side to side. Now you will notice a curious
effect, for the bands will glitter and become tinged with prismatic
colours, till, as it moves more and more rapidly these colours,
reflected in the jelly, seem to tinge the whole ball with colours like
those on a soap-bubble, while from the two sacs below come forth two
long transparent threads like spun glass. At first these appear to be
simple threads, but as they gradually open out to about four or five
inches, smaller threads uncoil on each side of the line till there are
about fifty on each line. These short _tendrils_ are never still for
long; as the main threads wave to and fro, some of the shorter ones coil
up and hang like tiny beads, then these uncoil and others roll up, so
that these graceful floating lines are never two seconds alike.
We do not really know their use. Sometimes the creature anchors itself
by them, rising and falling as they stretch out or coil up; but more
often they float idly behind it in the water. At first you would perhaps
think that they served to drive the ball through the water, but this is
done by a special apparatus. The cross ridges which we noticed on the
bands are really flat comb-like plates (_p_, Fig. 71), of which there
are about twenty or thirty on each band; and these vibrate very rapidly,
so that two hundred or more paddles drive the tiny ball through the
water. This is the cause of the prismatic colours; for iridescent tints
are produced by the play of light upon the glittering plates, as they
incessantly change their angle. Sometimes they move all at once,
sometimes only a few at a time, and it is evident the creature controls
them at will.
This lovely fairy-like globe, with its long floating tentacles and
rainbow tints, was for a long time classed with the jelly-fish; but it
really is most nearly related to sea-anemones, as it has a true central
cavity which acts as a stomach, and many other points in common with the
_Actinozoa_. We cannot help wondering, as the little being glides hither
and thither, whether it can see where it is going. It has nerves of a
low kind which start from a little dark spot (_ng_), exactly at the
south pole of the ball, and at that point a sense-organ of some kind
exists, but what impression the creature gains from it of the world
outside we cannot tell.
I am afraid you may think it dull to turn from such a beautiful being as
this, to the grey leaf which looks only like a dead dry seaweed; yet you
will be wrong, for a more wonderful history attaches to this crumpled
dead-looking leaf than to the lovely jelly-globe.
First of all I will pass round pieces of the dry leaf (_r_, Fig. 72),
and while you are getting them I will tell you where I found the living
ones. Great masses of the Flustra, as it is called, line the bottom and
sides of my pool. They grow in tufts, standing upright on the rock, and
looking exactly like hard grey seaweeds, while there is nothing to lead
you to suspect that they are anything else. Yesterday I chipped off very
carefully a piece of rock with a tuft upon it, and have kept it since in
a glass globe by itself with sea-water, for the little creatures living
in this marine city require a very good supply of healthy water and air.
I have called it a "marine city," and now I will tell you why. Take the
piece in your hand and run your finger gently up and down it; you will
glide quite comfortably from the lower to the higher part of the leaf,
but when you come back you will feel your finger catch slightly on a
rough surface. Your pocket lens will show why this is, for if you look
through it at the surface of the leaf you will see it is not smooth, but
composed of hundreds of tiny alcoves with arched tops; and on each side
of these tops stand two short blunt spines (see 2, Fig. 72), making four
in all, pointing upwards, so as partly to cover the alcove above. As
your finger went up it glided over the spines, but on coming back it met
their points. This is all you can see in the dead specimen; I must show
you the rest by diagrams, and by and by under the microscope.
[Illustration: Fig. 72.
The Sea-mat or Flustra (_Flustra foliacea._)
1, Natural size. 2, Much magnified. _s_, Slit caused by drawing in of
the animal _a_.]
First, then, in the living specimen which I have here, those alcoves are
not open as in the dead piece, but covered over with a transparent skin,
in which, near the top of the alcove just where the curve begins, is a
slit (_s_ 2, Fig. 72). Unfortunately the membrane covering this alcove
is too dense for you to distinguish the parts within. Presently,
however, if you are watching a piece of this living leaf in a flat
water-cell under the microscope, you will see the slit slowly open, and
begin to turn as it were inside out, exactly like the finger of a
glove, which has been pushed in at the tip, gradually rises up when you
put your finger inside it. As this goes on, a bundle of threads appears,
at first closed like a bud, but gradually opening out into a crown of
tentacles (_a_, Fig. 72), each one clothed with hairs. Then you will see
that the slit was not exactly a slit after all, but the round edge where
the sac was pushed in. Ah! you will say, you are now showing me a polyp
like those on the sertularian tree. Not so fast, my friend; you have not
yet studied what is still under the covering skin and hidden in the
living animal. I have, however, prepared a slide with this membrane
removed (see Fig. 73), and there you can observe the different parts,
and learn that each one of these alcoves contains a complete animal, and
not merely one among many mouths, like the polyp on the Sertularia.
[Illustration: Fig. 73.
Diagram of the animal in the Flustra or Sea-mat.
1, Animal protruding. 2, Animal retracted in the sheath. _sh_, Covering
sheath. _s_, Slit. _t_, Tentacles. _m_, Mouth. _th_, Throat. _st_,
Stomach. _i_, Intestine. _r_, Retractor muscle. _e_, Egg-forming parts.
_g_, Nerve-ganglion.]
Each of these little beings (_a_, Fig 72) living in its alcove has a
mouth, throat, stomach, intestine, muscles, and nerves starting from the
ganglion of nervous matter, besides all that is necessary for producing
eggs and sending forth young ones. You can trace all these under the
microscope (see 2, Fig. 73) as the creature lies curiously doubled up in
its bed, with its body bent in a loop; the intestine _i_, out of which
the refuse food passes, coming back close up to the slit. When it is at
rest, the top of the sac in which it lies is pulled in by the retractor
muscle _r_, and looks, as I have said, like the finger of a glove with
the top pushed in. When it wishes to feed, this top is drawn out by
muscles running round the sac, and the tentacles open and wave in the
water (1, Fig. 73).
Look now at the alcoves, the homes of these animals; see how tiny they
are and how closely they fit together. Mr. Gosse, the naturalist, has
reckoned that there are 6720 alcoves in a square inch; then if you turn
the leaf over you will see that there is another set, fixed back to back
with these, on the other side, making in all 13,440 alcoves. Now a
moderate-sized leaf of flustra measures about three square inches,
taking all the rounded lobes into account, so you will see we get 40,320
as a rough estimate of the number of beings on this one leaf. But if you
look at this tuft I have brought, you will find it is composed of twelve
such leaves, and this after all is a very small part of the mass growing
round my pool. Was I wrong, then, when I said that my miniature ocean
contains as many millions of beings as there are stars in the heavens?
You will want to know how these leaves grew, and it is in this way.
First a little free swimming animal, a mere living sac provided with
lashes, settles down and grows into one little horny alcove, with its
live creature inside, which in time sends off from it three to five
buds, forming alcoves all round the top and sides of the first one,
growing on to it. These again bud out, and you can thus easily
understand that, in this way, in time a good-sized leaf is formed.
Meanwhile the creatures also send forth new swimming cells, which settle
down near to begin new leaves, and thus a tuft is formed; and long after
the beings in earlier parts of the leaf have died and left their alcoves
empty, those round the margin are still alive and spreading.
With this history we must stop for to-day, and I expect it will be many
weeks before you have thoroughly examined the specimens of each kind
which I have put in the aquarium. If you can trace the spore-cells and
urns in the seaweeds, observe the polyps in the Sertularia, and count
the number of mouths on a branch of my animal fringe (_Sertularia
tenella_); if you make acquaintance with the Thuricolla in its vase, and
are fortunate enough to see one divide in two; if you learn to know some
of the beautiful forms of diatoms, and can picture to yourselves the
life of the tiny inhabitants of the Flustra; then you will have used
your microscope with some effect, and be prepared for an expedition to
my pool, where we will go together some day to seek new treasures.
CHAPTER IX
THE DARTMOOR PONIES,
OR
THE WANDERINGS OF THE HORSE TRIBE
[Illustration]
Put away the telescopes and microscopes to-day, boys, the holidays are
close at hand, and we will take a rest from peeping and peering till we
come back in the autumn laden with specimens for the microscope, while
the rapidly darkening evenings will tempt us again on to the lawn
star-gazing. On this our last lecture-day I want you to take a journey
with me which I took in imagination a few days ago, as I lay on my back
on the sunny moor and watched the Dartmoor ponies.
It was a calm misty morning one day last week, giving promise of a
bright and sunny day, when I started off for a long walk across the moor
to visit the famous stone-circles, many of which are to be found not
far off the track, called Abbot's Way, leading from Buckfast Abbey, on
the Dart, to the Abbey of Tavistock, on the Tavy.
My mind was full of the olden times as I pictured to myself how, seven
hundred years or more ago, some Benedictine monk from Tavistock Abbey,
in his black robe and cowl, paced this narrow path on his way to his
Cistercian brethren at Buckfast, meeting some of them on his road as
they wandered over the desolate moor in their white robes and black
scapularies in search of stray sheep. For the Cistercians were shepherds
and wool-weavers, while the Benedictines devoted themselves to learning,
and the track of about twenty-five miles from one abbey to the other,
which still remains, was worn by the members of the two communities and
their dependents, the only variety in whose lives consisted probably in
these occasional visits one to the other.
Yet even these monks belonged to modern times compared to the ancient
Britons who raised the stone-circles, and buried their dead in the
barrows scattered here and there over the moor; and my mind drifted back
to the days when, long before that pathway was worn, men clad in the
skins of beasts hunted wild animals over the ground on which I was
treading, and lived in caves and holes of the ground.
I wondered, as I thought of them, whether the cultured monks and the
uncivilised Britons delighted as much in the rugged scenery of the moor
as I did that morning. For many miles in front of me the moor stretched
out wild and treeless; the sun was shining brightly upon the mass of
yellow furze and deep-red heather, drawing up the moisture from the
ground, and causing a kind of watery haze to shimmer over the landscape;
while the early mist was rising off the _tors_, or hill-tops, in the
distance, curling in fanciful wreaths around the rugged and stony
summits, as it dispersed gradually in the increasing heat of the day.
The cattle which were scattered in groups here and there feeding on the
dewy grass were enjoying the happiest time of the year. The moor, which
in winter affords them scarcely a bare subsistence, is now richly
covered with fresh young grass, and the sturdy oxen fed solemnly and
deliberately, while the wild Dartmoor ponies and their colts scampered
joyously along, shaking their manes and long flowing tails, and neighing
to each other as they went; or clustered together on some verdant spot,
where the colts teased and bit each other for fun, as they gambolled
round their mothers.
It was a pleasure, there on the open moor, with the lark soaring
overhead, and the butterflies and bees hovering among the sweet-smelling
furze blossoms, to see horses free and joyous, with no thought of bit or
bridle, harness or saddle, whose hoofs had never been handled by the
shoeing-smith, nor their coats touched with the singeing iron. Those
little colts, with their thick heads, shaggy coats, and flowing tails,
will have at least two years more freedom before they know what it is to
be driven or beaten. Only once a year are they gathered together,
claimed by their owners and branded with an initial, and then left
again to wander where they will. True, it is a freedom which sometimes
has its drawbacks, for if the winter is severe the only food they can
get will be the furze-tops, off which they scrape the snow with their
feet; yet it is very precious in itself, for they can gallop when and
where they choose, with head erect, sniffing at the wind and crying to
each other for the very joy of life.
Now as I strolled across the moor and watched their gambols, thinking
how like free wild animals they seemed, my thoughts roamed far away, and
I saw in imagination scenes where other untamed animals of the horse
tribe are living unfettered all their lives long.
First there rose before my mind the level grass-covered pampas of South
America, where wild horses share the boundless plains with troops of the
rhea, or American ostrich, and wander, each horse with as many mares as
he can collect, in companies of hundreds or even thousands in a troop.
These horses are now truly wild, and live freely from youth to age,
unless they are unfortunate enough to be caught in the more inhabited
regions by the lasso of the hunter. In the broad pampas, the home of
herds of wild cattle, they dread nothing. There, as they roam with one
bold stallion as their leader, even beasts of prey hesitate to approach
them, for, when they form into a dense mass with the mothers and young
in their centre, their heels deal blows which even the fierce jaguar
does not care to encounter, and they trample their enemy to death in a
very short time. Yet these are not the original wild horses we are
seeking, they are the descendants of tame animals, brought from Europe
by the Spaniards to Buenos Ayres in 1535, whose descendants have
regained their freedom on the boundless pampas and prairies.
As I was picturing them careering over the plains, another scene
presented itself and took their place. Now I no longer saw around me
tall pampas-grass with the long necks of the rheas appearing above it,
for I was on the edge of a dreary scantily covered plain between the
Aral Sea and the Balkash Lake in Tartary. To the south lies a barren
sandy desert, to the north the fertile plains of the Kirghiz steppes,
where the Tartar feeds his flocks, and herds of antelopes gallop over
the fresh green pasture; and between these is a kind of no-man's land,
where low scanty shrubs and stunted grass seemed to promise but a poor
feeding-ground.
Yet here the small long-legged but powerful "Tarpans," the wild horses
of the treeless plains of Russia and Tartary, were picking their morning
meal. Sturdy wicked little fellows they are, with their shaggy
light-brown coats, short wiry manes, erect ears, and fiery watchful
eyes. They might well be supposed to be true wild horses, whose
ancestors had never been tamed by man; and yet it is more probable that
even they escaped in early times from the Tartars, and have held their
own ever since, over the grassy steppes of Russia and on the confines of
the plains of Tartary. Sometimes they live almost alone, especially on
the barren wastes where they have been seen in winter, scraping the snow
off the herbage as our ponies do on Dartmoor. At other times, as in the
south of Russia, where they wander between the Dnieper and the Don, they
gather in vast herds and live a free life, not fearing even the wolves,
which they beat to the ground with their hoofs. From one green oasis to
another they travel over miles of ground.
"A thousand horse--and none to ride!
With flowing tail, and flying mane,
Wide nostrils--never stretch'd by pain,
Mouths bloodless to the bit or rein,
And feet that iron never shod,
And flanks unscarr'd by spur or rod.
A thousand horse, the wild, the free,
Like waves that follow o'er the sea."[1]
[1] Byron's _Mazeppa_.
As I followed them in their course I fancied I saw troops of yet another
animal of the horse tribe, the "Kulan," or _Equus hemionus_, which is a
kind of half horse, half ass (Fig. 74), living on the Kirghiz steppes of
Tartary and spreading far beyond the range of the Tarpan into Tibet.
Here at last we have a truly wild animal, never probably brought into
subjection by man. The number of names he possesses shows how widely he
has spread. The Tartars call him "Kulan," the Tibetans "Kiang," while
the Mongolians give him the unpronounceable name of "Dschiggetai." He
will not submit to any of them, but if caught and confined soon breaks
away again to his old life, a "free and fetterless creature."
[Illustration: Fig. 74.
_Equus hemionus_, "Kiang" or "Kulan," the Horse-ass of Tartary and
Tibet. (Brehm.)]
No one has ever yet settled the question whether he is a horse or an
ass, probably because he represents an animal truly between the two.
His head is graceful, his body light, his legs slender and fleet, yet
his ears are long and ass-like; he has narrow hoofs, and a tail with a
tuft at the end like all the ass tribe; his colour is a yellow brown,
and he has a short dark mane and a long dark stripe down his back as a
donkey has, though this last character you may also see in many of our
Devonshire ponies. Living often on the high plateaux, sometimes as much
as 1500 feet above the sea, this "child of the steppes" travels in large
companies even as far as the rich meadows of Central Asia; in summer
wandering in green pastures, and in winter seeking the hunger-steppes
where sturdy plants grow. And when autumn comes the young steeds go off
alone to the mountain heights to survey the country around and call
wildly for mates, whom, when found, they will keep close to them through
all the next year, even though they mingle with thousands of others.
[Illustration: Fig. 75.
Przevalsky's Wild Horse, the "Kertag" or "Statur."]
Till about ten years ago the _Equus hemionus_ was the only truly wild
horse known, but in the winter of 1879-80 the Russian traveller
Przevalsky brought back from Central Asia a much more horse-like animal,
called by the Tartars "Kertag" and by the Mongols "Statur." It is a
clumsy, thick-set, whitish-gray creature with strong legs and a large,
heavy, reddish-coloured head; its legs have a red tint down to the
knees, beyond which they are blackish down to the hoofs. But the ears
are small, and it has the broad hoofs of the true horse, and warts on
his hind legs, which no animal of the ass tribe has. This horse, like
the Kiang, travels in small troops of from five to fifteen, led through
the wildest parts of the Dsungarian desert, between the Altai and
Tianschan Mountains, by an old stallion. They are extremely shy, and
see, hear, and smell very quickly, so that they are off like lightning
whenever anything approaches them.
So having travelled over America, Europe, and Asia, was my quest ended?
No; for from the dreary Asiatic deserts my thoughts wandered to a far
warmer and more fertile land, where between the Blue Nile and the Red
Sea rise the lofty highlands of Abyssinia, among which the African wild
ass (_Asinus tæniopus_), the probable ancestor of our donkeys, feeds in
troops on the rich grasses of the slopes, and then onwards to the bank
of a river in Central Africa where on the edge of a forest, with rich
pastures beyond, elephants and rhinoceroses, antelopes and buffaloes,
lions and hyænas, creep down in the cool of the evening to slake their
thirst in the flowing stream. There I saw the herds of Zebras in all
their striped beauty coming down from the mountain regions to the north,
and mingling with the darker-coloured but graceful quaggas from the
southern plains, and I half-grieved at the thought how these untamed and
free rovers are being slowly but surely surrounded by man closing in
upon them on every side.
I might now have travelled still farther in search of the Onager, or
wild ass of the Asiatic and Indian deserts, but at this point a more
interesting and far wider question presented itself, as I flung myself
down on the moor to ponder over the early history of all these tribes.
Where have they all come from? Where shall we look for the first
ancestors of these wild and graceful animals? For the answer to this
question I had to travel back to America, to those Western United States
where Professor Marsh has made such grand discoveries in horse history.
For there, in the very country where horses were supposed never to have
been before the Spaniards brought them a few centuries ago, we have now
found the true birthplace of the equine race.
Come back with me to a time so remote that we cannot measure it even by
hundreds of thousands of years, and let us visit the territories of Utah
and Wyoming. Those highlands were very different then from what they are
now. Just risen out of the seas of the Cretaceous Period, they were then
clothed with dense forests of palms, tree-ferns, and screw-pines,
magnolias and laurels, interspersed with wide-spreading lakes, on the
margins of which strange and curious animals fed and flourished. There
were large beasts with teeth like the tapir and the bear, and feet like
the elephant; and others far more dangerous, half bear, half hyæna,
prowling around to attack the clumsy paleotherium or the anoplotherium,
something between a rhinoceros and a horse, which grazed by the
waterside, while graceful antelopes fed on the rich grass. And among
these were some little animals no bigger than foxes, with four toes and
a splint for the fifth, on their front feet, and three toes on the hind
ones.
These clumsy little animals, whose bones have been found in the rocks of
Utah and Wyoming, have been called _Eohippus_, or horses of the dawn,
by naturalists. They were animals with real toes, yet their bones and
teeth show that they belonged to the horse tribe, and already the fifth
toe common to most other toed animals was beginning to disappear.
This was in the Eocene period, and before it passed away with its
screw-pines and tree-ferns, another rather larger animal, called the
_Orohippus_, had taken the place of the small one, and he had only four
toes on his front feet. The splint had disappeared, and as time went on
still other animals followed, always with fewer toes, while they gained
slender fleet legs, together with an increase in size and in
gracefulness. First one as large as a sheep (_Mesohippus_) had only
three toes and a splint. Then the splint again disappeared, and one
large and two dwindling toes only remained, till finally these two
became mere splints, leaving one large toe or hoof with almost
imperceptible splints, which may be seen on the fetlock of a horse's
skeleton.
The diagram (Fig 76) shows these splints in the horse's or ass's foot of
to-day. For you must notice that a horse's foot really begins at the
point _w_ which we call his knee in the front legs, and at his hock _h_
in the hind legs. His true knee _k_ and elbow _e_ are close up to the
body. What we call his foot or hoof is really the end of the strong,
broad, middle toe _t_ covered with a hoof, and farther up his foot at
_s_ and _s_ we can feel two small splints, which are remains of two
other toes.
Meanwhile during these long succeeding ages while the foot was
lengthening out into a slender limb the animals became larger, more
powerful, and more swift, the neck and head became longer and more
graceful, the brain-case larger in front and the teeth decreased in
number, so that there is now a large gap between the biting teeth _i_
and the grinding teeth _g_ of a horse. Their slender limbs too became
more flexible and fit for running and galloping, till we find the whole
skeleton the same in shape, though not in size, as in our own horses and
asses now.
[Illustration: Fig. 76.
Skeleton of Horse or Ass.
_i_, Incisor teeth. _g_, Grinding teeth, with the gap between the two as
in all grass-feeders. _k_, Knee. _h_, Hock or heel. _f_, Foot. _s_,
Splints or remains of the two lost toes. _e_, Elbow. _w_, Wrist. _ha_,
Hand-bone. _t_, middle toe of three joints, 1, 2, 3 forming the hoof.]
They did not, however, during all this time remain confined to America,
for, from the time when they arrived at an animal called _Miohippus_, or
lesser horse, which came after the Mesohippus and had only three toes
on each foot, we find their remains in Europe, where they lived in
company with the giraffes, opossums, and monkeys which roamed over these
parts in those ancient times. Then a little later we find them in Africa
and India; so that the horse tribe, represented by creatures about as
large as donkeys, had spread far and wide over the world.
And now, curiously enough, they began to forsake, or to die out in, the
land of their birth. Why they did so we do not know; but while in the
old world as asses, quaggas, and zebras, and probably horses, they
flourished in Asia, Europe, and Africa, they certainly died out in
America, so that ages afterwards, when that land was discovered, no
animal of the horse tribe was found in it.
And the true horse, where did he arise? Born and bred probably in
Central Asia from some animal like the "Kulan," or the "Kertag," he
proved too useful to savage tribes to be allowed his freedom, and it is
doubtful whether in any part of the world he escaped subjection. In our
own country he probably roamed as a wild animal till the savages, who
fed upon him, learned in time to put him to work; and when the Romans
came they found the Britons with fine and well-trained horses.
Yet though tamed and made to know his master he has, as we have seen,
broken loose again in almost all parts of the world--in America on the
prairies and pampas, in Europe and Asia on the steppes, and in Australia
in the bush. And even in Great Britain, where so few patches of
uncultivated land still remain, the young colts of Dartmoor, Exmoor,
and Shetland, though born of domesticated mothers, seem to assert their
descent from wild and free ancestors as they throw out their heels and
toss up their heads with a shrill neigh, and fly against the wind with
streaming manes and outstretched tails as the Kulan, the Tarpan, and the
Zebra do in the wild desert or grassy plain.
CHAPTER X
THE MAGICIAN'S DREAM OF ANCIENT DAYS.
[Illustration]
The magician sat in his armchair in the one little room in the house
which was his, and his only, besides the observatory. And a strange room
it was. The walls were hung with skulls and bones of men and animals,
with swords, daggers, and shields, coats of mail, and bronze
spear-heads. The drawers, many of which stood open, contained
flint-stones chipped and worn, arrowheads of stone, jade hatchets
beautifully polished, bronze buckles and iron armlets; while scattered
among these were pieces of broken pottery, some rough and only
half-baked, others beautifully finished, as the Romans knew how to
finish them. Rough needles made of bone lay beside bronze knives with
richly-ornamented handles and, most precious of all, on the table by the
magician's side lay a reindeer antler, on which was roughly carved the
figure of the reindeer itself.
He had been enjoying a six weeks' holiday, and he had employed it in
visiting some of the bone caves of Europe to learn about the men who
lived in them long, long ago. He had been to the south of France to see
the famous caves of the Dordogne, to Belgium to the caves of Engis and
Engihoul, to the Hartz Mountains and to Hungary. Then hastening home he
had visited the chief English caves in Yorkshire, Wales, and Devonshire.
Now that he had returned to his college, his mind was so full of facts,
that he felt perplexed how to lay before his class the wonderful story
of the life of man before history began. And as the day was hot, and the
very breeze which played around him made him feel languid and sleepy, he
fell into a reverie--a waking dream.
* * * * *
First the room faded from his sight, then the trim villages disappeared;
the homesteads, the corn-fields, the grazing cattle, all were gone, and
he saw the whole of England covered with thick forests and rough
uncultivated land. From the mountains in the north, glaciers were to be
seen creeping down the valleys between dense masses of fir and oak, pine
and birch; while the wild horse, the bison, and the Irish elk were
feeding on the plains. As he looked southward and eastward he saw that
the sea no longer washed the shores, for the English and Irish Channels
were not yet scooped out. The British Isles were still part of the
continent of Europe, so that animals could migrate overland from the
far south, up to what is now England, Scotland, and Ireland. Many of
these animals, too, were very different from any now living in the
country, for in the large rivers of England he saw the hippopotamus
playing with her calf, while elephants and rhinoceroses were drinking at
the water's edge. Yet these strange creatures did not have all the
country to themselves--wolves, bears, and foxes prowled in the woods,
large beavers built their dams across the streams, and here and there
over the country human beings were living in caves and holes of the
earth.
It was these men chiefly who attracted the magician's attention, and
being curious to know how they lived, he turned towards a cave, at the
mouth of which was a group of naked children who were knocking pieces of
flint together, trying to strike off splinters and make rough flint
tools, such as they saw their fathers use. Not far off from them a woman
with a wild beast's skin round her waist was gathering firewood, another
was grubbing up roots, and another, venturing a little way into the
forest, was searching for honey in the hollows of the tree trunks.
All at once in the dusk of the evening a low growl and a frightened cry
were heard, and the women rushed towards the cave as they saw near the
edge of the forest a huge tiger with sabre-shaped teeth struggling with
a powerful stag. In vain the deer tried to stamp on his savage foe or to
wound him with his antlers; the strong teeth of the tiger had penetrated
his throat, and they fell struggling together as the stag uttered his
death-cry. Just at that moment loud shouts were heard in the forest, and
the frightened women knew that help was near.
[Illustration: Fig. 77.
Palæolithic times.]
One after another, several men, clothed in skins hung over one shoulder
and secured round the waist, rushed out of the thicket, their hair
streaming in the wind, and ran towards the tiger. They held in their
hands strange weapons made of rough pointed flints fastened into handles
by thongs of skin, and as the tiger turned upon them with a cry of rage
they met him with a rapid shower of blows. The fight raged fiercely,
for the beast was strong and the weapons of the men were rude, but the
tiger lay dead at last by the side of his victim. His skin and teeth
were the reward of the hunters, and the stag he had killed became their
prey.
How skilfully they hacked it to pieces with their stone axes, and then
loading it upon their shoulders set off up the hill towards the cave,
where they were welcomed with shouts of joy by the women and children!
[Illustration: Fig. 78.
Palæolithic relics.
1, Bone needle, from a cave at La Madeleine, ½ size. 2, Tooth of
Machairodus or sabre-toothed tiger, from Kent's Cavern, ½ size. 3, Rough
stone implement, from Kent's Cavern, ¼ size.]
Then began the feast. First fires were kindled slowly and with
difficulty by rubbing a sharp-pointed stick in a groove of softer wood
till the wood-dust burst into flame; then a huge pile was lighted at the
mouth of the cave to cook the food and keep off wild beasts. How the
food was cooked the magician could not see, but he guessed that the
flesh was cut off the bones and thrust in the glowing embers, and he
watched the men afterwards splitting open the uncooked bones to suck out
the raw marrow which savages love.
After the feast was over he noticed how they left these split bones
scattered upon the floor of the cave mingling with the sabre-shaped
teeth of the tiger, and this reminded him of the bones of the stag and
the tiger's tooth which he had found in Kent's Cavern in Devonshire only
a few days before.
By this time the men had lain down to sleep, and in the darkness strange
cries were heard from the forest. The roar of the lion, mingled with the
howling of the wolves and the shrill laugh of the hyænas, told that they
had come down to feed on the remains of the tiger. But none of these
animals ventured near the glowing fire at the mouth of the cavern,
behind which the men slept in security till the sun was high in the
heavens. Then all was astir again, for weapons had been broken in the
fight, and some of the men sitting on the ground outside the cave placed
one flint between their knees, and striking another sharply against it
drove off splinters, leaving a pointed end and cutting edge. They
spoiled many before they made one to their liking, and the entrance to
the cave was strewn with splintered fragments and spoilt flints, but at
last several useful stones were ready. Meanwhile another man, taking his
rude stone axe, set to work to hew branches from the trees to form
handles, while another, choosing a piece remaining of the body of the
stag, tore a sinew from the thigh, and threading it through the large
eye of the bone needle, stitched the tiger's skin roughly together into
a garment.
"_This, then_," said the magician to himself, "_is how ancient man lived
in the summer-time, but how would he fare when winter came?_" As he
mused the scene gradually changed. The glaciers crept far lower down
the valleys, and the hills, and even the lower ground, lay thick in
snow. The hippopotamus had wandered away southward to warmer climes, as
animals now migrate over the continent of America in winter, and with
him had gone the lion, the southern elephant, and other summer visitors.
In their place large herds of reindeer and shaggy oxen had come down
from the north and were spread over the plains, scraping away the snow
with their feet to feed on the grass beneath. The mammoth, too, or hairy
elephant, of the same extinct species as those which have been found
frozen in solid ice under a sandbank in Siberia, had come down to feed,
accompanied by the woolly rhinoceros; and scattered over the hills were
the curious horned musk-sheep, which have long ago disappeared off the
face of the earth. Still, bitterly cold as it was, the hunter clad in
his wild-beast skin came out from time to time to chase the mammoth, the
reindeer, and the oxen for food, and cut wood in the forest to feed the
cavern fires.
This time the magician's thoughts wandered down to the south-west of
France, where, on the banks of a river in that part now called the
Dordogne, a number of caves not far from each other formed the home of
savage man. Here he saw many new things, for the men used arrows of
deer-horn and of wood pointed with flint, and with these they shot the
birds, which were hovering near in hopes of finding food during the
bitter weather. By the side of the river a man was throwing a small dart
of deer-horn fastened to a cord of sinews, with which from time to time
he speared a large fish and drew it to the bank.
[Illustration: Fig. 79.
Mammoth engraved on ivory by Palæolithic man.]
But the most curious sight of all, among such a rude people, was a man
sitting by the glowing fire at the mouth of one of the caves scratching
a piece of reindeer horn with a pointed flint, while the children
gathered round him to watch his work. What was he doing? See! gradually
the rude scratches began to take shape, and two reindeer fighting
together could be recognised upon the horn handle. This he laid
carefully aside, and taking a piece of ivory, part of the tusk of a
mammoth, he worked away slowly and carefully till the children grew
tired of watching and went off to play behind the fire. Then the
magician, glancing over his shoulder, saw a true figure of the mammoth
scratched upon the ivory, his hairy skin, long mane, and up-curved tusks
distinguishing him from all elephants living now. "_Ah_," exclaimed the
magician aloud, "_that is the drawing on ivory found in the cave of La
Madeleine in Dordogne, proving that man existed ages ago, and even knew
how to draw figures, at a time when the mammoth, or hairy elephant, long
since extinct, was still living on the earth!_"
With these words he started from his reverie, and knew that he had been
dreaming of Palæolithic man who, with his tools of rough flints, had
lived in Europe so long ago that his date cannot be fixed by years, or
centuries, or even thousands of years. Only this is known, that, since
he lived, the mammoth, the sabre-toothed tiger, the cave-bear, the
woolly rhinoceros, the cave-hyæna, the musk-sheep, and many other
animals have died out from off the face of the earth; the hippopotamus
and the lion have left Europe and retired to Africa, and the sea has
flowed in where land once was, cutting off Great Britain and Ireland
from the continent.
How long all these changes were in taking place no one knows. When the
magician drifted back again into his dream the land had long been
desolate, and the hyænas, which had always taken possession of the caves
whenever the men deserted them for awhile, had now been undisturbed for
a long time, and had left on the floor of the cave gnawed skulls and
bones, and jaws of animals, more or less scored with the marks of their
teeth, and these had become buried in a thick layer of earth. The
magician knew that these teeth marks had been made by hyænas, both
because living hyænas leave exactly such marks on bones in the present
day, and because the hyæna bones alone were not gnawed, showing that no
animals preyed upon their flesh. He knew too that the hyænas had been
there long after man had ceased to use the caves, because no flint
tools were found among the bones. But now the age of hyænas, too, was
past and gone, and the caves had been left so long undisturbed that in
many of them the water dripping from the roof had left film after film
of carbonate of lime upon the floor, which as the centuries went by
became a layer of stalagmite many feet thick, sealing down the secrets
of the past.
* * * * *
The face of the country was now entirely changed. The glaciers were
gone, and so, too, were all the strange animals. True, the reindeer, the
wild ox, and even here and there the Irish elk, were still feeding in
the valleys; wolves and bears still made the country dangerous, and
beavers built their dams across the streams, which were now much smaller
than formerly, and flowed in deeper channels, carved out by water during
the interval; but the elephants, rhinoceroses, lions, and tigers were
gone never to return, and near the caves in which some of the people
lived, and the rude underground huts which formed the homes of others,
tame sheep and goats were lying with dogs to watch them. Also, though
the land was still covered with dense forests, yet here and there small
clearings had been made, where patches of corn and flax were growing.
Naked children still played about as before, but now they were moulding
cups of clay like those in which food was being cooked on the fire
outside the caves or huts. Some of the women, dressed partly in skins of
beasts, partly in rough woven linen, were spinning flax into thread,
using as a spinning-whorl a small round stone with a hole in the middle
tied to the end of the flax, as a weight to enable them to twirl it.
Others were grinding corn in the hollow of a large stone by rubbing
another stone within it.
[Illustration: Fig. 80.
Neolithic implements.
1, Stone hatchet mounted in wood. 2, Jade celt, a polished stone weapon,
from Livermore in Suffolk, ¼ size. 3, Spindle whorl, ½ size.]
The men, while they still spent much time in hunting, had now other
duties in tending the sheep and goats, or looking after the hogs as they
turned up the ground in the forest for roots, or sowing and reaping
their crops. Yet still all the tools were made of stone, no longer rough
and merely chipped like the old stone weapons, but neatly cut and
polished. Stone axes with handles of deer-horn, stone spears and
javelins, stone arrowheads beautifully finished, sling-stones and
scrapers, were among their weapons and tools, and with them they made
many delicate implements of bone. On the broad lakes which here and
there broke the monotony of the forests, canoes, made of the trunks of
trees hollowed out by fire, were being paddled by one man, while
another threw out his fishing line armed with delicate bone-hooks; and
on the banks of the lakes, nets weighted with drilled stones tied on to
the meshes were dragged up full of fish.
For these Neolithic men, or men of the New Stone Period, who used
polished stone weapons, were farmers and shepherds and fishermen. They
knew how to make rude pottery, and kept domestic animals. Moreover, they
either came from the east or exchanged goods by barter with tribes
living more to the eastward, now that canoes enabled them to cross the
sea; for many of their weapons were made of greenstone or jade, and of
other kinds of stone not to be found in Europe, and their sheep and
goats were animals of eastern origin. They understood how to unite to
protect their homes, for they made underground huts by digging down
several feet into the ground and roofing the hole over with wood coated
with clay; and often long passages underground united these huts, while
in many places on the hills, camps, made of ramparts of earth surrounded
by ditches, served as strongholds for the women and children and the
flocks and herds, when some neighbouring tribe attacked their
homesteads.
Still, however, where caves were ready to hand they used them for
houses, and the same shelter which had been the home of the ancient
hunters, now resounded with the voices of the shepherds, who, treading
on the sealed floor, little dreamt that under their feet lay the remains
of a bygone age.
[Illustration: Fig. 81.
A burial in Neolithic times.]
And now, as our dreamer watched this new race of men fashioning their
weapons, feeding their oxen, and hunting the wild stag, his attention
was arrested by a long train of people crossing a neighbouring plain,
weeping and wailing as they went. At the head of this procession, lying
on a stretcher made of tree-boughs, lay a dead chieftain, and as the
line moved on, men threw down their tools, and women their spinning, and
joined the throng. On they went to where two upright slabs of stone with
another laid across them formed the opening to a long mound or chamber.
Into this the bearers passed with lighted torches, and in a niche ready
prepared placed the dead chieftain in a sitting posture with the knees
drawn up, placing by his side his flint spear and polished axe, his
necklace of shells, and the bowl from which he had fed. Then followed
the funeral feast, when, with shouts and wailing, fires were lighted,
and animals slaughtered and cooked, while the chieftain was not
forgotten, but portions were left for his use, and then the earth was
piled up again around the mouth of the chamber, till it should be opened
at some future time to place another member of his family by his side,
or till in after ages the antiquary should rifle his resting-place to
study the mode of burial in the Neolithic or Polished Stone Age.
Time passed on in the magician's dream, and little by little the caves
were entirely deserted as men learnt to build huts of wood and stone.
And as they advanced in knowledge they began to melt metals and pour
them into moulds, making bronze knives and hatchets, swords and spears;
and they fashioned brooches and bracelets of bronze and gold, though
they still also used their necklaces of shells and their polished stone
weapons. They began, too, to keep ducks and fowls, cows and horses; they
knew how to weave in looms, and to make cloaks and tunics; and when they
buried their dead it was no longer in a crouching position. They laid
them decently to rest, as if in sleep, in the barrows where they are
found to this day with bronze weapons by their side.
Then as time went on they learnt to melt even hard iron, and to beat it
into swords and plough-shares, and they lived in well-built huts with
stone foundations. Their custom of burial, too, was again changed, and
they burnt their dead, placing the ashes in a funeral urn.
[Illustration: Fig. 82.
British relics.
1, A coin of the age of Constantine. 2, Bronze weapon from a Suffolk
barrow. 3, Bronze bracelet from Liss in Hampshire.]
By this time the Britons, as they were now called, had begun to gather
together in villages and towns, and the Romans ruled over them. Now when
men passed through the wild country they were often finely dressed in
cloth tunics, wearing arm rings of gold, some even driving in
war-chariots, carrying shields made of wickerwork covered with leather.
Still many of the country people who laboured in the field kept their
old clothing of beast skins; they grew their corn and stored it in
cavities of the rocks; they made basket-work boats covered with skin, in
which they ventured out to sea. So things went on for a long period till
at last a troubled time came, and the quiet valleys were disturbed by
wandering people who fled from the towns and took refuge in the
forests; for the Romans after three hundred and fifty years of rule had
gone back home to Italy, and a new and barbarous people called the
Jutes, Angles, and Saxons, came over the sea from Jutland and drove the
Britons from their homes.
[Illustration: Fig. 83.
Britons taking refuge in the Cave.]
And so once more the caves became the abode of man, for the harassed
Britons brought what few things they could carry away from their houses
and hid themselves there from their enemies. How little they thought, as
they lay down to sleep on the cavern floor, that beneath them lay the
remains of two ages of men! They knew nothing of the woman who had
dropped her stone spindle-whorl into the fire, on which the food of
Neolithic man had been cooking in rough pots of clay; they never dug
down to the layer of gnawed bones, nor did they even in their dreams
picture the hyæna haunting his ancient den, for a hyæna was an animal
they had never seen. Still less would they have believed that at one
time, countless ages before, their island had been part of the
continent, and that men, living in the cave where they now lay, had cut
down trees with rough flints, and fought with such unknown animals as
the mammoth and the sabre-toothed tiger.
But the magician saw it all passing before him, even as he also saw
these Britons carrying into the cave their brooches, bracelets, and
finger rings, their iron spears and bronze daggers, and all their little
household treasures which they had saved in their flight. And among
these, mingling in the heap, he recognised Roman coins bearing the
inscription of the Emperor Constantine, and he knew that it was by these
coins that he had, a few days before in Yorkshire, been able to fix the
date of the British occupation of a cave.
* * * * *
And with this his dream ended, and he found himself clutching firmly the
horn on which Palæolithic man had engraved the figure of the reindeer.
He rose, and stretching himself crossed the sunny grass plot of the
quadrangle and entered his classroom. The boys wondered as he began his
lecture at the far-away look in his eyes. They did not know how he had
passed through a vision of countless ages; but that afternoon, for the
first time, they realised, as he unfolded scene after scene, the history
of "The Men of Ancient Days."
INDEX
Abbot's Way across Dartmoor, 196
Absorption of rays of sunlight, 129
Abyssinia, wild ass of, 203
_Actinozoa_, Cydippe allied to the, 190
Ages, lapse of between old and new stone age, 217
Alcor, or Jack, 158
Aldebaran, 149;
called so by the Arabs, 153;
colour of, 167
Algol the Variable, 162, 165
Almach, [Greek: g] Andromedæ, 156;
a coloured double star, 167
America, extinction of original horse in, 207
Andromeda, the great nebula of, 162, 164;
double coloured star in, 167
Animal of the Sea-mat, 191;
number in one leaf, 193
Animal-trees and stony plants, 178
Animals, extinct, living with man, 211
Antares, a ruby-red star, 167
Antherozoids of mosses, 89
Apothecia of lichens, 83
Apennines, Lunar, figured, 19
Archimedes, a lunar crater, 10;
smooth centre of, 19
Arctic lands, lichens in, 82
Arcturus, colour of, 166
Aristarchus, a lunar crater, 10, 24;
streaks around, 17
Aristotle, a lunar crater, 10
Arrows, old stone, 215
Asia, horse of Central, 201
_Asinus tæniopus_, 203
_Aspergillus glaucus_, 61;
growth of, 63
Ass tribe, forms allied to the, 201
Ass, wild of Africa, 203
Atmosphere, absence of in the moon, 21
Australia, wild horses of, 207
_Bacillaria Paradoxa_, a diatom, 185
Bacteria growing on wounds, 66
Baiæ, hill thrown up on Bay of, 103
Ball, Sir R., on binary stars, 154
Beehive, triple star near the, 168
Beer, fermentation of, 65
Bellatrix, a star in Orion, 148
Berlin, ground beneath, formed of diatoms, 186
Bessel, on movements of Sirius, 169
Betelgeux, a star in Orion, 148
Binary star in Great Bear, 157, 158
Binary stars, 154, 166, 170
Bog-moss or Sphagnum, 93
Bog-mosses, distribution of, 94
Bombs, volcanic, 105
Boötis [Greek: e], a coloured double star, 167
Britons inhabiting caves, 224;
ornaments and customs of, 223
Britons of Dartmoor, 196
Bronze weapon and bracelet, 223
Bryum or thread moss, 77
Buckfast Abbey, monks of, 196
Bunt, a fungus, 64
Burial in Neolithic times, 221
Cassiopeia, the constellation, 162;
coloured double star in, 167
Castor, a binary star, 154
Camera, photographic, 47;
attached to the telescope, 121
Cancer [Greek: z], a triple coloured star, 168
Candle-flame, image of, formed by lens, 33
Canis Major, constellation of, 148
Capella, colour of the star, 153
Castor, light of compared with a near star, 158
Caterpillars destroyed by fungus, 66
Caucasus Mountains on the Moon, 18
Cave, the three periods of a, 225
Caves, Palæolithic and Neolithic, 210;
Palæolithic life in, 211;
hyænas roamed in, 217;
Neolithic life in, 218;
Britons took refuge in, 224
Cells, fertile of mushroom, 69;
of moss-plant, 89
Celt, jade, from Suffolk, 219
Chambers, Mr., his drawing of [Greek: e] Lyræ, 166
Charles's Wain, 155;
part of Great Bear, 157;
stars of drifting, 159;
stars visible in waggon of, 160;
double coloured star in, 158, 167
_Chilomonas amygdalum_, a monad, 182
Ciliary muscle, action of the, 34
Clark, Alvan, on companion of Sirius, 169
Clockwork of telescope, 2
_Cocconema lanceolatum_, a diatom, 184
Coin of age of Constantine, 223
_Confervæ_, growth of, 79
Commons, Mr., photographed Orion's nebula, 152
Constantine, coin of age of, 223
Constellations, maps of, 148, 156
Copernicus, a lunar crater, 10, 24;
figured, 17;
bright streaks around, 18
Copper-sulphate in lava, 108
_Corallina_, a stony seaweed, 175;
fruit of, 177;
appearance like _Sertularia_, 179
Cornea of the eye, 31
Corona, nature of the sun's, 123, 137
Cottam, Mr. A., his plate of coloured stars, 167
Crater, lava flowing from a, 98;
interior of Vesuvius, 100
Crater-plains, 19-21
Craters on the moon, 10, 13, 17, 19, 20;
of earth and moon compared, 16
Crystallites in volcanic glass, 109
Crystallisation, two periods of, in lava, 115
Crystals forming in artificial lavas, 114;
precious, 116
_Cydippe pileus_, a living jelly-ball, 187;
structure of, 188-190
Cygni [Greek: b], a coloured double star, 167
Dartmoor, fairy rings on, 57, 58;
the Sundew on, 56;
granite figured, 112;
ponies, 195
De la Rue, his photograph of moon, 13
Devonshire ponies, black stripe on, 201
Diatom, a growing, 185
_Diatoma hyalina_, 184
Diatoms, magnified fossil, 39;
living marine, 184
Didymium, giving a broken spectrum, 126
Dordogne, caves of the, 210, 215
Draper, Prof., photographed Orion's nebula, 152
_Drosera rotundifolia_ on Dartmoor, 56
Dschiggetai, horse-ass of Tibet, 200
Dsungarian desert, wild horse of the, 203
Dykes, nature of volcanic, 111
Earth, path of the moon round the, 8;
magnetic storm on, caused by sun, 14;
reservoirs of melted matter in the, 101
Earthquakes accompanying volcanic outbursts, 102
Eclipse of sun, red jets and corona seen during, 125
Eclipse, total, of the moon, 23;
lurid light during, 25
Eclipses, how caused, 7
Elephant, hairy, engraved on ivory, 216
_Empusa muscæ_, 66
Engis and Engihoul caves, 210
England, ancient caves in, 210;
in Palæolithic times, 211
Eocene, toed horses of the, 205
_Eohippus_, or horse of the dawn, 205
_Equus hemionus_, the horse-ass, 202
Eratosthenes, a lunar crater, 10
Erbia, giving a broken spectrum, 126
Ergot, a fungus, 61
Eruptions of Vesuvius, 97, 100, 104
Eudoxus, a lunar crater, 10
Experiments, necessity for accurate, 54
Eye, structure of the, 29-32;
mode of seeing with the, 32;
short-sighted, 29, 35;
distances spanned by the naked, 40
Faculæ on the sun's face, 122, 140
Fairy rings, 55;
mentioned in _Merry Wives of Windsor_, 57;
growth of, 71-73
Ferments caused by fungi, 60, 64
Fishing in ancient times, 215, 220
_Fistulina hepatica_, a fungus, 71
Flint skeletons of plants, 185
Flustra or sea-mat, 187;
structure of, 191-193
Fly, fungus killing a, 66
Focal images, 33;
distances, 44
Fouqué, M., artificial lava made by, 112
Fructification of mushrooms, 69;
of lichens, 83;
of mosses, 91;
of seaweeds, 177
_Funaria hygrometrica_, urn of the, 89, 91;
has no urn lid, 92
Fungi, nature of, 59;
different kinds of, 60;
attacking insects, 66;
growing on wounds, 66;
the use of, 74
Fungus and green cells in lichen, 81
Gardener, advice of the old, 118
Gas, spectrum of a, 126
Gases revealed by spectroscope, 52
Gemini, the constellation, 154
Geminorum, [Greek: d], a double coloured star, 167
Gills of mushroom, 69
_Gomphonema marinum_, 184
Gooseberry, fermentation in a, 64
Gory dew, _Palmella cruenta_, 79
Graham's island thrown up, 102
Granular appearance of sun's face, 123
Grape fungus, 65
Great Bear, the constellation, 157;
binary star in, 158;
coloured double star in, 158, 168
Greenstone, Neolithic weapons of, 220
Guards, the, in the Little Bear, 162
Hartz Mountains, caves of the, 210
Hatchet, a Neolithic stone, 219
Hebrides, volcanic islands of, 111
Henri, MM., photograph of moon's face by, 19
Herculaneum, buried, 98, 104
Herculis [Greek: a], a coloured double star, 168
Hermitage, lava stream flowing behind the, 97, 99
Herschel's drawing of Copernicus, 17
Huggins, Dr., on shape of prominences, 135;
on spectra of nebulæ, 151;
on cause of colour in stars, 168
Himalayas, single-celled plants in the, 79
Horse, wild, of the Pampas, 198;
of Tartary, 199;
of Kirghiz steppes, 200;
Przevalsky's, 202;
early history of toed, 204;
structure of foot and hoof of, 205;
skeleton of, 206;
origin and migration of early, 207
Hungary, ancient caves of, 210
Huyghens, the highest peak in Lunar Apennines, 19
Image formed at focus of lens, 33;
of sky in telescope, 49
Implements, old stone, 213;
new stone, 219
Imps of plant-life, 59
India, low plants in springs of, 79;
solar eclipse seen in, 124;
wild ass of, 203
Infusorial earth, 186
Infusorians in a seaside pool, 183
Inhabitants of a seaside pool, 172-174
Iris of the eye, 30
Iron pyrites in lava, 108
Iron slag, lava compared to, 105
Islands, volcanic thrown up, 102
Jack by the second horse, 157
Jade, Neolithic weapons of, 220
Jannsen, Prof., on sun prominences, 131
Judd, Mr., on volcano of Mull, 111
Jutes and Angles invading Britain, 224
Kant on nebular hypothesis, 152
Kent's Cavern, rough stone implement from, 213
Kepler, a lunar crater, 10;
streaks around, 17
Kertag, or wild horse, 202
Kew, sun-storm registered at, 143
Kiang or Kulan, 200
Kirchhoff, Prof., on sunlight, 128
Kulan or Kiang, 200
Labrador felspar artificially made, 113
Langley, Prof., sun-spot drawn by, 141
Laplace, nebular hypothesis of, 152
Lava, aspect of flowing, 99;
reservoirs of molten, 101;
nature of, 107;
artificially made, 113;
two periods of crystallisation in, 115
Lava-stream, history of a, 100;
section of a, 108;
rapid cooling of surface, 108
Laver or sea-lettuce, structure of, 176
Leo, the constellation, 155
Leucotephrite artificially made, 113
Lens, natural, of the eye, 31;
simple magnifying, 35
Levy, M., artificial lava made by, 112
Lichens, specimens of from life, 77;
the life-history of, 80-84;
sections of, 81;
distribution of 82, 95;
fructification of, 83;
causes of success of, 94
Lick telescope, magnifying power of, 46
Light, lurid, on moon during eclipse, 24;
sifted by spectroscope, 126
Light-granules on sun's face, 123;
supposed explanation of, 141
Lime-tree, fungi on the, 64
Liss, bronze bracelet from, 223
Little Bear, pole-star and guards in the, 162
Lockyer, Mr., on sun-prominences, 131, 136
Lunar Apennines figured, 19
Lyræ [Greek: epsilon], a double-binary star, 166
Machairodus, tooth of, 213
Madeleine, La, carvings from cave of, 216
Magic glasses and how to use them, 27;
what can be done by, 28, 53
Magician's chamber, 1;
his pupils, 4;
spells, 28;
his dream of ancient days, 209
Magnetic connection of sun and earth, 142
Magnifying-glass, action of a, 35
Mammoth engraved on ivory, 216
Maps of constellations, 148, 156
_Marasmius oreastes_, fairy-ring mushroom, 55, 72
_Mazeppa_, quotation from Byron's, 201
Men of older stone age, 212;
of Neolithic age, 218
_Mesohippus_, a toed horse, 205
Microliths in volcanic glass, 109, 110, 113, 115;
formed in artificial lava, 113
Microscope, 3;
action of the, 36-38
Mildews are fungi, 60
Milky Way, 149;
Cassiopeia in the, 163
Minerals crystallising in lava, 108
Mines, increase of temperature in, 101
Miohippus, or lesser toed horse, 206
Mizar, a double-coloured star in the Great Bear, 158, 168
Monads, size and activity of, 183
Monks, ancient, of Dartmoor, 196
Monte Nuovo thrown up in 1538, 103
Moon, phases of the, 6;
course in the heavens, 8;
map of the, 10;
craters of the, 10, 13, 17, 19, 20;
face of full, 11;
a worn-out planet, 21;
no atmosphere in the, 21;
diagram of eclipse of, 23;
lurid light on during eclipse, 24
Moss-leaf magnified, 87
Moss, life-history of a, 84, 92;
a stem of feathery, 85;
protonema of a, 86;
modes of new growth of a, 88;
fructification of a, 89;
urns of a, 89, 91
Mosses, different kinds of, 77;
advantages and distribution of, 94
Moulds are fungi, 60;
how they grow, 63
Mountains of the moon, 19;
formation of, 21
_Mucor Mucedo_, figured, 61;
growth of, 63
Mull, volcanic dykes in the island of, 111
Mushroom, early stages and spawn of, 67;
mycelium of, 67;
later stages of, 68;
section of gills of, 69;
spores of, 70;
fairy or Scotch bonnet, 72
Mycelium of mould, 63;
of mushroom, 67;
of fairy rings, 72
Naples, volcanic eruption seen at, 96;
Monte Nuovo thrown up near, 103
Nasmyth on bright lunar streaks, 16
Nebula of Orion, 149;
spectrum of, 151;
photographs of, 152;
of Pleiades, 153;
of Andromeda, 163-164
Needle, bone, from a cave, 212
Neolithic implements, 219;
industries and habits, 218-220;
burials, 221
Neptune, invisible to naked eye, 35
Neison, Mr., his drawing of Plato, 20
_Nostoc_, growing on stones, 79
Oak, fungi on the, 64
Observatory, the Magician's, 2;
astronomical on Vesuvius, 97;
cascade of lava behind the, 99
Obsidian, or volcanic glass, 109
Occultation of a star, 22, 25
Onager, or wild ass of Asia, 203
Optic nerve of eye, 34
Orion, constellation of, 147, 149;
great nebula of, 149;
photographs of Nebula of, 152;
coloured double stars in, 168
Orionis [Greek: th], or Trapezium, 150
Ornaments of ancient Britons, 222
Orohippus, a toed horse, 205
_Oscillariæ_, growth of, 79
Palæolithic man, 212;
relics, 213;
life, 214, 216
Pampas, wild horses of the, 198
_Penicillium glaucum_, figured, 61;
growth of, 63
Penumbra of an eclipse, 23;
of sun-spots, 140
Perithecia of lichens, 84
Petavius, a lunar crater, 10
Photographic camera, 3, 47;
attached to telescope, 121
Photographs of the moon, 13, 19;
of galloping horse, 48;
of the stars, 49, 161;
of the sun, 121
Photosphere of the sun, 123
Philadelphia, electric shocks at during sun-storm, 143
Pixies of plant life, 59
Plains of the moon, 10;
nature of the, 12
Plants, colourless, single-celled, 65;
single-celled green, 78;
two kinds of in lichens, 80;
with flint skeletons, 185
Plato, a lunar crater, 10, 24;
figured, 20
Pleiades, the, 153;
nebulæ in, 153
_Pleurococcus_, a single-celled plant, 78
Plough, the, or Charles's Wain, 157
Pointers, in Charles's Wain, 161
Pole-star, the, 161;
a yellow sun, 166
Pollux, a yellow sun, 166
_Polysiphonia_, a red seaweed, 175;
fruit of, 177
_Polytrichum commune_, a hair moss, 88;
its urns protected by a lid, 91
Pool, inhabitants of a seaside, 172-74
Precious stones, formation of, 116
Proctor, his star atlas, 146;
on drifting of Charles's Wain, 159
Prominence-spectrum and sun-spectrum compared, 134
Prominences, red, of the sun, 125;
seen in full daylight, 131-133;
shape of, 135
_Protococcus nivalis_, 79
Protonema of a moss, 86
Przevalsky's wild horse, 202
Ptolemy, a lunar crater, 10
Puffballs, 67, 70;
use of in nature, 73
Pupil of the eye, 30
Puzzuoli, eruption near, 1538, 103
Quaggas, herds of, 203
Rain-band in the solar spectrum, 130
Rain-shower during volcanic eruption, 107
Readings in the sky, 53, 127, 151, 168
Red snow, a single-celled plant, 79
Regulus, the star, 155, 166
Reindeer, carving on horn of, 216
Reservoirs of molten rock underground, 101
Resina, ascent of Vesuvius from, 98
Retina of the eye, 31;
image of object on the, 33
Richmond, Virginia, infusorial earth of, 186
Rigel, a star in Orion, 149;
a coloured double star, 168
Rings, growth of fairy, 73
Roberts, Mr. I., his photograph of Orion's nebula, 152;
and of nebula of the Pleiades, 153;
and of nebula of Andromeda, 164
Rosse, Lord, his telescope, 46;
on Orion's nebula, 150;
stars visible in his telescope, 160
Rue, De la, his photograph of the moon, 13
Rust on plants, 61
Sabrina island formed, 102
Saturn, distance of, 40
Saxons, invasion of the, 224
Schwabe, Herr, on sun-spots cycle, 137
Scoriæ of volcanoes, 108
"Scotch bonnet" mushroom, 72
Sea-mat, _see_ Flustra
"Seas" lunar, so-called, 10
Seaweeds, a group of, 175;
fruits of, 177
Secchi, Father, on depth of a sun-spot, 139
Selwyn, Mr., photograph of sun by, 122
Senses alone tell us of outer world, 29
_Sertularia tenella_, structure of, 180;
_cupressina_, 181
Sertularian and coralline, resemblance of, 179
Shakespeare on fairy rings, 57
Shipley, Mr., saw volcanic island formed, 103
Sight, far and near, 35
Silkworm destroyed by fungi, 66
Sirius, 146;
a bluish white sun, 166;
irregularities of caused by a companion, 169
Skeleton of the horse, 206
Skin diseases caused by fungi, 61, 66
Sky, light readings in the, 53, 127, 151, 168
Smut, a fungus, 61
Sodium lime in the spectrum, 128
Somma, part of ancient Vesuvius, 97, 104
Spawn of mushroom, 67
Spectra, plate of coloured, 127
Spectroscope, 3;
Kirchhoff's, 51;
gases revealed by the, 52;
direct vision, 127;
sifting light, 126;
attached to telescope, 132
Spectrum of sunlight, 127, 130
Sphacelaria, a brown-green seaweed, 175;
fruit of, 177
Sphagnum or bog moss, 77, 93;
structure of leaves of, 93
Spindle-whorl from Neolithic caves, 219
Spore-cases of mosses, 89, 91, 93
Spores of moulds, 63;
of mushroom, 70;
of lichens, 83;
of mosses, 91
Star, occultation of, by the moon, 24;
a double-binary, 166;
a dark, travelling round Sirius, 169
Star-cluster in Perseus, 162
Star-depths, 160, 171
Stars, light from the, 40, 42;
visible in the country, 145;
apparent motion of the, 146;
maps of, 148, 156;
of milky way, 149;
binary, 154;
real motion of, 159;
drifting, 159;
number of known and estimated, 161;
colours of, 166;
double coloured, 167;
cause of colour in, 168;
are they centres of solar systems? 170
Statur or wild horse, 202
Streaks, bright, on the moon, 14-17
Suffolk, bronze weapon from barrow in, 223
Sun, path of the moon round the, 8;
one of the stars, 119;
how to look at the, 119;
face of, thrown on a screen, 120;
photograph of the, 122;
prominences, corona, and faculæ of, 122-125;
mottling of face of, 123;
total eclipse of, 124;
zodiacal line round, 125;
dark lines in spectrum of, 128;
reversing layer of, 131;
metals in the, 131;
sudden outburst in the, 142;
magnetic connection with the earth, 143;
a yellow star, 166
Sun's rays touching moon during eclipse, 24
Sun-spots, cycle of, 137;
proving sun's rotation, 138;
nature of, 139;
quiet and unquiet, 140;
formation of, 142
Sundew on Dartmoor, 56
Tarpan, a wild horse, 199
Tartary, wild horses of, 199
Tavistock Abbey, monks of, 196
Telescope, clock-work, adjusting a, 2;
an astronomical, 41;
magnifying power of the, 43-46;
giant, 46;
terrestrial, 47;
what can be seen in a small, 46;
how the sun is photographed in the, 122;
how the spectroscope is worked with the, 132
Teneriffe, peak of compared to lunar craters, 15
Tennant, Major, drawing of eclipsed sun by, 123
Temperature, underground, 101
_Thuricolla follicula_, a transparent infusorian, 182
Tiger, sabre-toothed, 211, 213
_Tilletia caria_ or bunt, 64
Toadstools, 67, 70;
use of in nature, 73
Tools, of ancient stone period, 214, 215
Tooth of machairodus, 213
Torquay, the Magician's pool near, 172
Tors of Dartmoor, 197
Trapezium of Orion, 150
_Tremella mesenterica_ fungus, 71
Tripoli formed of diatoms, 35
Tundras, lichens and mosses of the, 82, 95
Tycho, a lunar crater, 10;
description of, 13;
bright streaks of, 14
_Ulva_, a green seaweed, 175;
a section magnified, 176
Umbra of an eclipse, 23
Urns of mosses, 89, 91
_Ustilago carbo_, or smut, 64
Variable stars, 165
Vega, a bluish-white sun, 166;
double-binary star near, 165
Veil of mushroom, 68
Vesuvian lavas imitated, 113
Vesuvius, eruption of 1868 described, 97, 99, 104;
dormant, 103;
eruption of in A.D. 79, 104
Volcanic craters of earth and moon compared, 16;
eruptions in the moon, 21;
glass under the microscope, 109, 110, 115
Volcano, diagram of an active, 105
Volcanoes, the cause of discussed, 101, 102;
ancient, laid bare, 111
Washington, electric shocks at during sun-storm, 143
Winter in Palæolithic times, 215
Wood, winter growth in a, 76
"World without End," 115
Yeast, growth of, 65
Yorkshire, Roman coins in caves of, 225
Zebra, herds of, 203
Zodiacal light, 125
THE END
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_CHINA: Travels and Investigations in the "Middle Kingdom."_ A
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the government and leading men."--_Boston Traveller._
_THE GARDEN'S STORY; or, Pleasures and Trials of an Amateur
Gardener._ By GEORGE H. ELLWANGER. With Head and Tail Pieces by
Rhead. 12mo. Cloth extra, $1.50.
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_THE FOLK-LORE OF PLANTS._ By T. F. THISELTON DYER, M.A. 12mo.
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"The Folk-Lore of Plants" traces the superstitions and fancies connected
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_FLOWERS AND THEIR PEDIGREES._ By GRANT ALLEN, author of
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delightful one, and the book is fascinating to any one who has either
love for flowers or curiosity about them."--_Hartford Courant._
_THE HISTORY OF ANCIENT CIVILIZATION._ A Hand-book based upon
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