The Project Gutenberg EBook of The Moon, by Thomas Gwyn Elger
This eBook is for the use of anyone anywhere at no cost and with
almost no restrictions whatsoever. You may copy it, give it away or
re-use it under the terms of the Project Gutenberg License included
with this eBook or online at www.gutenberg.org
Title: The Moon
A Full Description and Map of its Principal Physical Features
Author: Thomas Gwyn Elger
Release Date: February 7, 2006 [EBook #17712]
Language: English
*** START OF THIS PROJECT GUTENBERG EBOOK THE MOON ***
Produced by Steve Ridgway
THE MOON
A FULL DESCRIPTION AND MAP OF ITS PRINCIPAL PHYSICAL FEATURES
BY
THOMAS GWYN ELGER, F.R.A.S.
DIRECTOR OF THE LUNAR SECTION OF THE BRITISH ASTRONOMICAL ASSOCIATION
EX-PRESIDENT LIVERPOOL ASTRONOMICAL SOCIETY
"Altri fiumi, altri laghi, altre campagne
Sono la su che non son qui tra noi,
Altri piani, altre valli, altre montagne."
ORLANDO FURIOSO, Canto xxxii.
LONDON GEORGE PHILIP & SON,
32 FLEET STREET, E.C.
LIVERPOOL: 45 TO 51 SOUTH CASTLE STREET
1895
PREFACE
This book and the accompanying map is chiefly intended for the use of
lunar observers, but it is hoped it may be acceptable to many who, though
they cannot strictly be thus described, take a general interest in
astronomy.
The increasing number of those who possess astronomical telescopes, and
devote more or less of their leisure in following some particular line of
research, is shown by the great success in recent years of societies,
such as the British Astronomical Association with its several branches,
the Astronomical Society of the Pacific, and similar institutions in
various parts of the world. These societies are not only doing much in
popularising the sublimest of the sciences, but are the means of
developing and organising the capabilities of their members by
discouraging aimless and desultory observations, and by pointing out how
individual effort may be utilised and made of permanent value in almost
every department of astronomy.
The work of the astronomer, like that of the votary of almost every other
science, is becoming every year more and more specialised; and among its
manifold subdivisions, the study of the physical features of the moon is
undoubtedly increasing in popularity and importance. To those who are
pursuing such observations, it is believed that this book will be a
useful companion to the telescope, and convenient for reference.
Great care has been taken in the preparation of the map, which, so far as
the positions of the various objects represented are concerned, is based
on the last edition of Beer and Madler's chart, and on the more recent
and much larger and elaborate map of Schmidt; while as regards the shape
and details of most of the formations, the author's drawings and a large
number of photographs have been utilised. Even on so small a scale as
eighteen inches to the moon's diameter, more detail might have been
inserted, but this, at the expense of distinctness, would have detracted
from the value of the map for handy reference in the usually dim light of
the observatory, without adding to its utility in other ways. Every named
formation is prominently shown; and most other features of interest,
including the principal rill-systems, are represented, though, as regards
these, no attempt is made to indicate all their manifold details and
ramifications, which, to do effectually, would in very many instances
require a map on a much larger scale than any that has yet appeared.
The insertion of meridian lines and parallels of latitude at every ten
degrees, and the substitution of names for reference numbers, will add to
the usefulness of the map.
With respect to the text, a large proportion of the objects in the
Catalogue and in the Appendix have been observed and drawn by the author
many times during the last thirty years, and described in _The
Observatory_ and other publications. He has had, besides, the advantage
of consulting excellent sketches by Mr W.H. MAW, F.R.A.S., Dr. SHELDON,
F.R.A.S., Mr. A. MEE, F.R.A.S., Mr. G.P. HALLOWES, F.R.A.S., Dr. SMART,
F.R.A.S., Mr. T. GORDON, F.R.A.S., Mr. G.T. DAVIS, Herr BRENNER, Herr
KRIEGER, Mr. H. CORDER, and other members of the British Astronomical
Association. Through the courtesy of Professor HOLDEN, Director of the
Lick Observatory, and M. PRINZ, of the Royal Observatory of Brussels,
many beautiful photographs and direct photographic enlargements have been
available, as have also the exquisite heliogravures received by the
author from Dr. L. WEINEK, Director of the Imperial Observatory of
Prague, and the admirable examples of the photographic work of MM. PAUL
and PROSPER HENRY of the Paris Observatory, which are occasionally
published in _Knowledge_. The numerous representations of lunar objects
which have appeared from time to time in that storehouse of astronomical
information, _The English Mechanic_, and the invaluable notes in
"Celestial Objects for Common Telescopes," and in various periodicals, by
the late REV. PREBENDARY WEBB, to whom Selenography and Astronomy
generally owe so much, have also been consulted.
As a rule, all the more prominent and important features are described,
though very frequently interesting details are referred to which, from
their minuteness, could not be shown in the map. The measurements (given
in round numbers) are derived in most instances from NEISON'S (Nevill)
"Moon," though occasionally those in the introduction to Schmidt's chart
are adopted.
THOMAS GYWN ELGER.
BEDFORD, 1895.
CONTENTS
INTRODUCTION
MARIA, OR PLAINS, TERMED "SEAS"
RIDGES
RING-MOUNTAINS, CRATERS, &C.
Walled Plains
Mountain Rings
Ring-Plains
Craters
Crater Cones
Craterlets, Crater Pits
MOUNTAIN RANGES, ISOLATED MOUNTAINS, &c.
CLEFTS, OR RILLS
FAULTS
VALLEYS
BRIGHT RAY-SYSTEMS
THE MOON'S ALBEDO, SURFACE BRIGHTNESS, &c.
TEMPERATURE OF THE MOON'S SURFACE
LUNAR OBSERVATION
PROGRESS OF SELENOGRAPHY, LUNAR PHOTOGRAPHY
CATALOGUE OF LUNAR FORMATIONS
FIRST QUADRANT--
West Longitude 90 deg. to 60 deg.
West Longitude 60 deg. to 40 deg.
West Longitude 40 deg. to 20 deg.
West Longitude 20 deg. to 0 deg.
SECOND QUADRANT--
East Longitude 0 deg. to 20 deg.
East Longitude 20 deg. to 40 deg.
East Longitude 40 deg. to 60 deg.
East Longitude 60 deg. to 90 deg.
THIRD QUADRANT--
East Longitude 0 deg. to 20 deg.
East Longitude 20 deg. to 40 deg.
East Longitude 40 deg. to 60 deg.
East Longitude 60 deg. to 90 deg.
FOURTH QUADRANT--
West Longitude 90 deg. to 60 deg.
West Longitude 60 deg. to 40 deg.
West Longitude 40 deg. to 20 deg.
West Longitude 20 deg. to 0 deg.
MAP OF THE MOON
First Quadrant
Second Quadrant
Third Quadrant
Fourth Quadrant
APPENDIX
Description of Map
List of the Maria, or Grey Plains, termed "Seas," &c.
List of some of the most Prominent Mountain Ranges, Promontories,
Isolated Mountains, and Remarkable Hills
List of the Principal Ray-Systems, Light-Surrounded Craters, and
Light Spots
Position of the Lunar Terminator
Lunar Elements
Alphabetical List of Formations
INTRODUCTION
We know, both by tradition and published records, that from the earliest
times the faint grey and light spots which diversify the face of our
satellite excited the wonder and stimulated the curiosity of mankind,
giving rise to suppositions more or less crude and erroneous as to their
actual nature and significance. It is true that Anaxagoras, five
centuries before our era, and probably other philosophers preceding him,
--certainly Plutarch at a much later date--taught that these delicate
markings and differences of tint, obvious to every one with normal
vision, point to the existence of hills and valleys on her surface; the
latter maintaining that the irregularities of outline presented by the
"terminator," or line of demarcation between the illumined and
unillumined portion of her spherical superficies, are due to mountains
and their shadows; but more than fifteen centuries elapsed before the
truth of this sagacious conjecture was unquestionably demonstrated.
Selenography, as a branch of observational astronomy, dates from the
spring of 1609, when Galileo directed his "optic tube" to the moon, and
in the following year, in the _Sidereus Nuncius_, or "the Intelligencer
of the Stars," gave to an astonished and incredulous world an account of
the unsuspected marvels it revealed. In this remarkable little book we
have the first attempt to represent the telescopic aspect of the moon's
visible surface in the five rude woodcuts representing the curious
features he perceived thereon, whose form and arrangement, he tells us,
reminded him of the "ocelli" on the feathers of a peacock's tail,--a
quaint but not altogether inappropriate simile to describe the appearance
of groups of the larger ring-mountains partially illuminated by the sun,
when seen in a small telescope.
The bright and dusky areas, so obvious to the unaided sight, were found
by Galileo to be due to a very manifest difference in the character of
the lunar surface, a large portion of the northern hemisphere, and no
inconsiderable part of the south-eastern quadrant, being seen to consist
of large grey monotonous tracts, often bordered by lofty mountains, while
the remainder of the superficies was much more conspicuously brilliant,
and, moreover, included by far the greater number of those curious ring-
mountains and other extraordinary features whose remarkable aspect and
peculiar arrangement first attracted his attention. Struck by the analogy
which these contrasted regions present to the land and water surfaces of
our globe, he suspected that the former are represented on the moon by
the brighter and more rugged, and the latter by the smoother and more
level areas; a view, however, which Kepler more distinctly formulated in
the dictum, "Do maculas esse Maria, do lucidas esse terras." Besides
making a rude lunar chart, he estimated the heights of some of the ring-
mountains by measuring the distance from the terminator of their bright
summit peaks, when they were either coming into or passing out of
sunlight; and though his method was incapable of accuracy, and his
results consequently untrustworthy, it served to demonstrate the immense
altitude of these circumvallations, and to show how greatly they exceed
any mountains on the earth if the relative dimensions of the two globes
are taken into consideration.
Before the close of the century when selenography first became possible,
Hevel of Dantzig, Scheiner, Langrenus (cosmographer to the King of
Spain), Riccioli, the Jesuit astronomer of Bologna, and Dominic Cassini,
the celebrated French astronomer, greatly extended the knowledge of the
moon's surface, and published drawings of various phases, and charts,
which, though very rude and incomplete, were a clear advance upon what
Galileo, with his inferior optical means, had been able to accomplish.
Langrenus, and after him Hevel, gave distinctive names to the various
formations, mainly derived from terrestrial physical features, for which
Riccioli subsequently substituted those of philosophers, mathematicians,
and other celebrities; and Cassini determined by actual measurement the
relative position of many of the principal objects on the disc, thus
laying the foundation of an accurate system of lunar topography; while
the labours of T. Mayer and Schroter in the last century, and of
Lohrmann, Madler, Neison (Nevill), Schmidt, and other observers in the
present, have been mainly devoted to the study of the minuter detail of
the moon and its physical characteristics.
As was manifest to the earliest telescopic observers, its visible surface
is clearly divisible into strongly contrasted areas, differing both in
colour and structural character. Somewhat less than half of what we see
of it consists of comparatively level dark tracts, some of them very many
thousands of square miles in extent, the monotony of whose dusky
superficies is often unrelieved for great distances by any prominent
object; while the remainder, everywhere manifestly brighter, is not only
more rugged and uneven, but is covered to a much greater extent with
numbers of quasi-circular formations, differing widely in size, classed
as walled-plains, ring-plains, craters, craterlets, crater-cones, &c.
(the latter bearing a great outward resemblance to some terrestrial
volcanoes), and mountain ranges of vast proportions, isolated hills, and
other features.
Though nothing resembling sheets of water, either of small or large
extent, have ever been detected on the surface, the superficial
resemblance, in small telescopes, of the large grey tracts to the
appearance which we may suppose our terrestrial lakes and oceans would
present to an observer on the moon, naturally induced the early
selenographers to term them Maria, or "seas"--a convenient name, which
is still maintained, without, however, implying that these areas, as we
now see them, are, or ever were, covered with water. Some, however,
regard them as old sea-beds, from which every trace of fluid, owing to
some unknown cause, has vanished, and that the folds and wrinkles, the
ridges, swellings, and other peculiarities of structure observed upon
them, represent some of the results of alluvial action. It is, of course,
possible, and even probable, that at a remote epoch in the evolution of
our satellite these lower regions were occupied by water, but that their
surface, as it now appears, is actually this old sea-bottom, seems to be
less likely than that it represents the consolidated crust of some semi-
fluid or viscous material (possibly of a basaltic type) which has welled
forth from orifices or rents communicating with the interior, and
overspread and partially filled up these immense hollows, more or less
overwhelming and destroying many formations which stood upon them before
this catastrophe took place. Though this, like many other speculations of
a similar character relating to lunar "geology," must remain, at least
for the present, as a mere hypothesis; indications of this partial
destruction by some agency or other is almost everywhere apparent in
those formations which border the so-called seas, as, for example,
Fracastorius in the Mare Nectaris; Le Monnier in the Mare Serenitatis;
Pitatus and Hesiodus, on the south side of the Mare Nubium; Doppelmayer
in the Mare Humorum, and in many other situations; while no observer can
fail to notice innumerable instances of more or less complete
obliteration and ruin among objects within these areas, in the form of
obscure rings (mere scars on the surface), dusky craters, circular
arrangements of isolated hills, reminding one of the monoliths of a
Druidical temple; all of which we are justified in concluding were at one
time formations of a normal type. It has been held by some selenologists
--and Schmidt appears to be of the number,--that, seeing the comparative
scarcity of large ring-plains and other massive formations on the Maria,
these grey plains represent, as it were, a picture of the primitive
surface of the moon before it was disturbed by the operations of interior
forces; but this view affords no explanation of the undoubted existence
of the relics of an earlier lunar world beneath their smooth superficies.
MARIA.--Leaving, however, these considerations for a more particular
description of the Maria, it is clearly impossible, in referring to their
level relatively to the higher and brighter land surface of the moon, to
appeal to any hypsometrical standard. All that is known in this respect
is, that they are invariably lower than the latter, and that some sink to
a greater depth than others, or, in other words, that they do not all
form a part of the same sphere. Though they are more or less of a
greyish-slaty hue--some of them approximating very closely to that of the
pigment known as "Payne's grey"--the tone, of course, depends upon the
angle at which the solar rays impinge on that particular portion of the
surface under observation. Speaking generally, they are, as would follow
from optical considerations, conspicuously darker when viewed near the
terminator, or when the sun is either rising or setting upon them, than
under a more vertical angle of illumination. But even when it is possible
to compare their colour by eye-estimation under similar solar altitudes,
it is found that not only are some of the Maria, as a whole, notably
darker than others, but nearly all of them exhibit _local_ inequalities
of hue, which, under good atmospheric and instrumental conditions, are
especially remarkable. Under such circumstances I have frequently seen
the surface, in many places covered with minute glittering points of
light, shining with a silvery lustre, intermingled with darker spots and
a network of streaks far too delicate and ethereal to represent in a
drawing. In addition to these contrasts and differences in the sombre
tone of these extended plains, many observers have remarked traces of a
yellow or green tint on the surface of some of them. For example, the
Mare Imbrium and the Mare Frigoris appear under certain conditions to be
of a dirty yellow-green hue, the central parts of the Mare Humorum dusky
green, and part of the Mare Serenitatis and the Mare Crisium light green,
while the Palus Somnii has been noted a golden-brown yellow. To these may
be added the district round Taruntius in the Mare Foecunditatis, and
portions of other regions referred to in the catalogue, where I have
remarked a very decided sepia colour under a low sun. It has been
attempted to account for these phenomena by supposing the existence of
some kind of vegetation; but as this involves the presence of an
atmosphere, the idea hardly finds favour at the present time, though
perhaps the possibility of plant growth in the low-lying districts, where
a gaseous medium may prevail, is not altogether so chimerical a notion as
to be unworthy of consideration. Nasmyth and others suggest that these
tints may be due to broad expanses of coloured volcanic material, an
hypothesis which, if we believe the Maria to be overspread with such
matter, and knowing how it varies in colour in terrestrial volcanic
regions, is more probable than the first. Anyway, whether we consider
these appearances to be objective, or, after all, only due to purely
physiological causes, they undoubtedly merit closer study and
investigation than they have hitherto received.
There are twenty-three of these dusky areas which have received
distinctive names; seventeen of them are wholly, or in great part,
confined to the northern, and to the south-eastern quarter of the
southern hemisphere--the south-western quadrant being to a great extent
devoid of them. By far the largest is the vast Oceanus Procellarum,
extending from a high northern latitude to beyond latitude 10 deg. in the
south-eastern quadrant, and, according to Schmidt, with its bays and
inflections, occupying an area of nearly two million square miles, or
more than that of all the remaining Maria put together. Next in order of
size come the Mare Nubium, of about one-fifth the superficies, covering a
large portion of the south-eastern quadrant, and extending considerably
north of the equator, and the Mare Imbrium, wholly confined to the
northeastern quadrant, and including an area of about 340,000 square
miles. These are by far the largest lunar "seas." The Mare Foecunditatis,
in the western hemisphere, the greater part of it lying in the south-
western quadrant, is scarcely half so big as the Mare Imbrium; while the
Maria Serenitatis and Tranquilitatis, about equal in area (the former
situated wholly north of the equator, and the latter only partially
extending south of it), are still smaller. The arctic Mare Frigoris, some
100,000 square miles in extent, is the only remaining large sea,--the
rest, such as the Mare Vaporum, the Sinus Medii, the Mare Crisium, the
Mare Humorum, and the Mare Humboldtianum, are of comparatively small
dimensions, the Mare Crisium not greatly exceeding 70,000 square miles,
the Mare Humorum (about the size of England) 50,000 square miles, while
the Mare Humboldtianum, according to Schmidt, includes only about 42,000
square miles, an area which is approached by some formations not classed
with the Maria. This distinction, speaking generally, prevails among the
Maria,--those of larger size, such as the Oceanus Procellarum, the Mare
Nubium, and the Mare Foecunditatis, are less definitely enclosed, and,
like terrestrial oceans, communicate with one another; while their
borders, or, if the term may be allowed, their coast-line, is often
comparatively low and ill-defined, exhibiting many inlets and
irregularities in outline. Others, again, of considerable area, as, for
example, the Mare Serenitatis and the Mare Imbrium, are bounded more or
less completely by curved borders, consisting of towering mountain
ranges, descending with a very steep escarpment to their surface: thus in
form and other characteristics they resemble immense wall-surrounded
plains. Among the best examples of enclosed Maria is the Mare Crisium,
which is considered by Neison to be the deepest of all, and the Mare
Humboldtianum.
Though these great plains are described as level, this term must only be
taken in a comparative sense. No one who observes them when their surface
is thrown into relief by the oblique rays of the rising or setting sun
can fail to remark many low bubble-shaped swellings with gently rounded
outlines, shallow trough-like hollows, and, in the majority of them, long
sinuous ridges, either running concentrically with their borders or
traversing them from side to side. Though none of these features are of
any great altitude or depth, some of the ridges are as much as 700 feet
in height, and probably in many instances the other elevations often rise
to 150 feet or more above the low-lying parts of the plains on which they
stand. Hence we may say that the Maria are only level in the sense that
many districts in the English Midland counties are level, and not that
their surface is absolutely flat. The same may be said as to their
apparent smoothness, which, as is evident when they are viewed close to
the terminator, is an expression needing qualification, for under these
conditions they often appear to be covered with wrinkles, flexures, and
little asperities, which, to be visible at all, must be of considerable
size. In fact, were it possible to examine them from a distance of a few
miles, instead of from a standpoint which, under the most favourable
circumstances, cannot be reckoned at less than 300, and this through an
interposed aerial medium always more or less perturbed, they would
probably be described as rugged and uneven, as some modern lava sheets.
RIDGES.--Among the Maria which exhibit the most remarkable arrangement of
ridges is the Mare Humorum, in the south-eastern quadrant. Here, if it be
observed under a rising sun, a number of these objects will be seen
extending from the region north of the ring-mountain Vitello in long
undulating lines, roughly concentric with the western border of the
"sea," and gradually diminishing in altitude as they spread out, with
many ramifications, to a distance of 200 miles or more towards the north.
At this stage of illumination they are strikingly beautiful in a good
telescope, reminding one of the ripple-marks left by the tide on a soft
sandy beach. Like most other objects of their class, they are very
evanescent, gradually disappearing as the sun rises higher in the lunar
firmament, and ultimately leaving nothing to indicate their presence
beyond here and there a ghostly streak or vein of a somewhat lighter hue
than that of the neighbouring surface. The Mare Nectaris, again, in the
south-western quadrant, presents some fine examples of concentric ridges,
which are seen to the best advantage when the morning sun is rising on
Rosse, a prominent crater north of Fracastorius. This "sea" is evidently
concave in cross-section, the central portion being considerably lower
than the margin, and these ridges appear to mark the successive stages of
the change of level from the coast-line to the centre. They suggest the
"caving in" of the surface, similar to that observed on a frozen pond or
river, where the "cat's ice" at the edge, through the sinking of the
water beneath, is rent and tilted to a greater or less degree. The Mare
Serenitatis and the Mare Imbrium, in the northern hemisphere, are also
remarkable for the number of these peculiar features. They are very
plentifully distributed round the margin and in other parts of the
former, which includes besides one of the longest and loftiest on the
moon's visible surface--the great serpentine ridge, first drawn and
described nearly a hundred years ago by the famous selenographer,
Schroter of Lilienthal. Originating at a little crater under the north-
east wall of great ring-plain Posidonius, it follows a winding course
across the Mare toward the south, throwing out many minor branches, and
ultimately dies out under a great rocky promontory--the Promontory
Acherusia, at the western termination of the Haemus range. A
comparatively low power serves to show the curious structural character
of this immense ridge, which appears to consist of a number of
corrugations and folds massed together, rising in places, according to
Neison, to a height of 700 feet and more. The Mare Imbrium also affords
an example of a ridge, which, though shorter, is nearly as prominent, in
that which runs from the bright little ring-plain Piazzi Smyth towards
the west side of Plato. The region round Timocharis and other quarters of
the Mare are likewise traversed by very noteworthy features of a similar
class. The Oceanus Procellarum also presents good instances of ridges in
the marvellous ramifications round Encke, Kepler, and Marius, and in the
region north of Aristarchus and Herodotus. Perhaps the most perfect
examples of surface swellings are those in the Mare Tranquilitatis, a
little east of the ring-plain Arago, where there are two nearly equal
circular mounds, at least ten miles in diameter, resembling tumuli seen
from above. Similar, but more irregular, objects of a like kind are very
plentiful in many other quarters.
It is a suggestive peculiarity of many of the lunar ridges, both on the
Maria and elsewhere, that they are very generally found in association
with craters of every size. Illustrations of this fact occur almost
everywhere. Frequently small craters are found on the summits of these
elevations, but more often on their flanks and near their base. Where a
ridge suddenly changes its direction, a crater of some prominence
generally marks the point, often forming a node, or crossing-place of
other ridges, which thus appear to radiate from it as a centre. Sometimes
they intrude within the smaller ring-mountains, passing through gaps in
their walls as, for example, in the cases of Madler, Lassell, &c. Various
hypotheses have been advanced to account for them. The late Professor
Phillips, the geologist, who devoted much attention to the telescopic
examination of the physical features of the moon, compared the lunar
ridges to long, low, undulating mounds, of somewhat doubtful origin,
called "kames" in Scotland, and "eskers" in Ireland, where on the low
central plain they are commonly found in the form of extended banks
(mainly of gravel), with more or less steep sides, rising to heights of
from 20 to 70 feet. They are sometimes only a few yards wide at the top,
while in other places they spread out into large humps, having circular
or oval cavities on their summits, 50 or 60 yards across, and as much as
40 feet deep. Like the lunar ridges, they throw out branches and exhibit
many breaches of continuity. By some geologists they are supposed to
represent old submarine banks formed by tidal currents, like harbour
bars, and by others to be glacial deposits; in either case, to be either
directly or indirectly due to alluvial action. Their outward resemblance
to some of the ridges on the moon is unquestionable; and if we could
believe that the Maria, as we now see them, are dried-up sea-beds, it
might be concluded that these ridges had a similar origin; but their
close connection with centres of volcanic disturbance, and the numbers of
little craters on or near their track, point to the supposition that they
consist rather of material exuded from long-extending fissures in the
crust of the "seas," and in other surfaces where they are superimposed.
This conjecture is rendered still more probable by the fact that we
sometimes find the direction of clefts (which are undoubted surface
cracks) prolonged in the form of long narrow ridges or of rows of little
hillocks. We are, however, not bound to assume that all the manifold
corrugations observed on the lunar plains are due to one and the same
cause; indeed, it is clear that some are merely the outward indications
of sudden drops in the surface, as in the case of the ridges round the
western margin of the Mare Nectaris, and in other situations, where
subsidence is manifested by features assuming the outward aspect of
ordinary ridges, but which are in reality of a very different structural
character.
The Maria, like almost every other part of the visible surface, abound in
craters of a minute type, which are scattered here and there without any
apparent law or ascertained principle of arrangement. Seeing how
imperfect is our acquaintance with even the larger objects of this class,
it is rash to insist on the antiquity or permanence of such diminutive
objects, or to dogmatise about the cessation of lunar activity in
connection with features where the volcanic history of our globe, if it
is of any value as an analogue, teaches us it is most likely to prevail.
Most observers will agree with Schmidt, that observations and drawings of
objects on the sombre depressed plains of the moon are easier and
pleasanter to make than on the dazzling highlands, and that the lunar
"sea" is to the working selenographer like an oasis in the desert to the
traveller--a relief in this case, however, not to an exhausted body, but
to a weary eye.
RING-MOUNTAINS, CRATERS, &C.--It is these objects, in their almost
endless variety and bewildering number, which, more than any others, give
to our satellite that marvellous appearance in the telescope which since
the days of Galileo has never failed to evoke the astonishment of the
beholder. However familiar we may be with the lunar surface, we can never
gaze on these extraordinary formations, whether massed together
apparently in inextricable confusion, or standing in isolated grandeur,
like Copernicus, on the grey surface of the plains, without experiencing,
in a scarcely diminished degree, the same sensation of wonder and
admiration with which they were beheld for the first time. Although the
attempt to bring all these _bizarre_ forms under a rigid scheme of
classification has not been wholly successful, their structural
peculiarities, the hypsometrical relation between their interior and the
surrounding district, their size, and the character of their
circumvallation, the dimensions of their cavernous opening as compared
with that of the more or less truncated conical mass of matter
surrounding it, all afford a basis for grouping them under distinctive
titles, that are not only convenient to the selenographer, but which
undoubtedly represent, as a rule, actual diversities in their origin and
physical character.
These distinguishing titles, as adopted by Schroter, Lohrmann, and
Madler, and accepted by subsequent observers, are WALLED-PLAINS, MOUNTAIN
RINGS, RING-PLAINS, CRATERS, CRATER-CONES, CRATERLETS, CRATER-PITS,
DEPRESSIONS.
WALLED-PLAINS.--These formations, approximating more or less to the
circular form, though frequently deviating considerably from it, are
among the largest enclosures on the moon. They vary from upwards of 150
to 60 miles or under in diameter, and are often encircled by a complex
rampart of considerable breadth, rising in some instances to a height of
12,000 feet or more above the enclosed plain. This rampart is rarely
continuous, but is generally interrupted by gaps, crossed by transverse
valleys and passes, and broken by more recent craters and depressions. As
a rule, the area within the circumvallation (usually termed "the floor")
is only slightly, if at all, lower than the region outside: it is very
generally of a dusky hue, similar to that of the grey plains or Maria,
and, like them, is usually variegated by the presence of hills, ridges,
and craters, and is sometimes traversed by delicate furrows, termed
clefts or rills.
_Ptolemaeus_, in the third quadrant, and not far removed from the centre
of the disc, may be taken as a typical example of the class. Here we have
a vast plain, 115 miles from side to side, encircled by a massive but
much broken wall, which at one peak towers more than 9000 feet above a
level floor, which includes details of a very remarkable character. The
adjoining _Alphonsus_ is another, but somewhat smaller, object of the
same type, as are also _Albategnius_, and _Arzachel_; and _Plato_, in a
high northern latitude, with its noble many-peaked rampart and its
variable steel-grey interior. _Grimaldi_, near the eastern limb (perhaps
the darkest area on the moon), _Schickard_, nearly as big, on the south-
eastern limb, and _Bailly_, larger than either (still farther south in
the same quadrant), although they approach some of the smaller "seas" in
size, are placed in the same category. The conspicuous central mountain,
so frequently associated with other types of ringed enclosures, is by no
means invariably found within the walled-plains; though, as in the case
of _Petavius_, _Langrenus_, _Gassendi_, and several other noteworthy
examples, it is very prominently displayed. The progress of sunrise on
all these objects affords a magnificent spectacle. Very often when the
rays impinge on their apparently level floor at an angle of from 1 deg.
to 2 deg., it is seen to be coarse, rough grained, and covered with
minute elevations, although an hour or so afterwards it appears as smooth
as glass.
Although it is a distinguishing characteristic that there is no great
difference in level between the outside and the inside of a walled-plain,
there are some very interesting exceptions to this rule, which are termed
by Schmidt "Transitional forms." Among these he places some of the most
colossal formations, such as _Clavius_, _Maurolycus_, _Stofler_,
_Janssen_, and _Longomontanus_. The first, which may be taken as
representative of the class (well known to observers as one of the
grandest of lunar objects), has a deeply sunken floor, fringed with
mountains rising some 12,000 feet above it, though they scarcely stand a
fourth of this height above the plain on the west, which ascends with a
very gentle gradient to the summit of the wall. Hence the contrast
between the shadows of the peaks of the western wall on the floor at
sunrise, and of the same peaks on the region west of the border at sunset
is very marked. In _Gassendi_, _Phocylides_, and _Wargentin_ we have
similar notable departures from the normal type. The floor of the former
on the north stands 2000 feet _above_ the Mare Humorum. In _Phocylides_,
probably through "faulting," one portion of the interior suddenly sinks
to a considerable depth below the remainder; while the very abnormal
_Wargentin_ has such an elevated floor, that, when viewed under
favourable conditions, it reminds one of a shallow oval tray or dish
filled with fluid to the point of overflowing. These examples, very far
from being exhaustive, will be sufficient to show that the walled-plains
exhibit noteworthy differences in other respects than size, height of
rampart, or included detail. Still another peculiarity, confined, it is
believed, to a very few, may be mentioned, viz., convexity of floor,
prominently displayed in Petavius, Mersenius, and Hevel.
MOUNTAIN RINGS.--These objects, usually encircled by a low and broken
border, seldom more than a few hundred feet in height, are closely allied
to the walled-plains. They are more frequently found on the Maria than
elsewhere. In some cases the ring consists of isolated dark sections,
with here and there a bright mass of rock interposed; in others, of low
curvilinear ridges, forming a more or less complete circumvallation. They
vary in size from 60 or 70 miles to 15 miles and less. The great ring
north of Flamsteed, 60 miles across, is a notable example; another lies
west of it on the north of Wichmann; while a third will be found south-
east of Encke;--indeed, the Mare Procellarum abounds in objects of this
type. The curious formation on the Mare Imbrium immediately south of
Plato (called "Newton" by Schroter), may be placed in this category, as
may also many of the low dusky rings of much smaller dimensions found in
many quarters of the Maria. As has been stated elsewhere, these features
have the appearance of having once been formations of a much more
prominent and important character, which have suffered destruction, more
or less complete, through being partially overwhelmed by the material of
the "seas."
RING-PLAINS.--These are by far the most numerous of the ramparted
enclosures of the moon, and though it is occasionally difficult to decide
in which class, walled-plain or ring-plain, some objects should be
placed, yet, as a rule, the difference between the structural character
of the two is abundantly obvious. The ring-plains vary in diameter from
sixty to less than ten miles, and are far more regular in outline than
the walled-plains. Their ramparts, often very massive, are more
continuous, and fall with a steep declivity to a floor almost always
greatly depressed below the outside region. The inner slopes generally
display subordinate heights, called terraces, arranged more or less
concentrically, and often extending in successive stages nearly down to
the interior foot of the wall. With the intervening valleys, these
features are very striking objects when viewed under good conditions with
high powers. In some cases they may possibly represent the effects of the
slipping of the upper portions of the wall, from a want of cohesiveness
in the material of which it is composed; but this hardly explains why the
highest terrace often stands nearly as high as the rampart. Nasmyth, in
his eruption hypothesis, suggests that in such a case there may have been
two eruptions from the same vent; one powerful, which formed the exterior
circle, and a second, rather less powerful, which has formed the interior
circle. Ultimately, however, coming to the conclusion that terraces, as a
rule, are not due to any such freaks of the eruption, he ascribes them to
landslips. In any case, we can hardly imagine that material standing at
such a high angle of inclination as that forming the summit ridge of many
of the ring-plains would not frequently slide down in great masses, and
thus form irregular plateaus on the lower and flatter portions of the
slope; but this fails to explain the symmetrical arrangement of the
concentric terraces and intermediate valleys. The inner declivity of the
north-eastern wall of Plato exhibits what to all appearance is an
undoubted landslip, as does also that of Hercules on the northern side,
and numerous other cases might be adduced; but in all of them the
appearance is very different from that of the true terrace.
The _glacis_, or outer slope of a ring-plain, is invariably of a much
gentler inclination than that which characterises the inner declivity:
while the latter very frequently descends at an angle varying from 60
deg. to 50 deg. at the crest of the wall, to from 10 deg. to 2 deg. at
the bottom, where it meets the floor; the former extends for a great
distance at a very flat gradient before it sinks to the general level of
the surrounding country. It differs likewise from the inner descent, in
the fact that, though often traversed by valleys, intersected by deep
gullies and irregular depressions, and covered with humpy excrescences
and craters, it is only rarely that any features comparable to the
terraces, usually present on the inner escarpment, can be traced upon it.
Elongated depressions of irregular outline, and very variable in size and
depth, are frequently found on the outer slopes of the border. Some of
them consist of great elliptical or sub-circular cavities, displaying
many expansions and contractions, called "pockets," and suggesting the
idea that they were originally distinct cup-shaped hollows, which from
some cause or other have coalesced like rows of inosculating craters.
While many of these features are so deep that they remain visible for a
considerable time under a low sun, others, though perhaps of greater
extent, vanish in an hour or so.
As in the case of the walled-plains, the ramparts of the ring-plains
exhibit gaps and are broken by craters and depressions, but to a much
less extent. Often the lofty crest, surmounted by _aiguilles_ or by
blunter peaks, towering in some cases to nearly double its altitude above
the interior, is perfectly continuous (like Copernicus), or only
interrupted by narrow passes. It is a suggestive circumstance that gaps,
other than valleys, are almost invariably found either in the north or
south walls, or in both, and seldom in other positions. The buttress, or
long-extending spur, is a feature frequently associated with the ring-
plain rampart, as are also numbers of what, for the lack of a better
name, must be termed little hillocks, which generally radiate in long
rows from the outer foot of the slope. The spurs usually abut on the
wall, and, either spreading out like the sticks of a fan or running
roughly parallel to each other, extend for long distances, gradually
diminishing in height and width till they die out on the surrounding
surface. They have been compared to lava streams, which those round
Aristillus, Aristoteles, and on the flank of Clavius _a_, certainly
somewhat resemble, though, in the two former instances, they are rather
comparable to immense ridges. In addition to the above, the spurs
radiating from the south-eastern rampart of Condamine and the long
undulating ridges and rows of hillocks running from Cyrillus over the
eastern _glacis_ of Theophilus, may be named as very interesting
examples.
Neison and some other selenographers place in a distinct class certain of
the smaller ring-plains which usually have a steeper outer slope, and are
supposed to present clearer indications of a volcanic origin than the
ring-plains, terming them "Crater-plains."
CRATERS.--Under this generic name is placed a vast number of formations
exhibiting a great difference in size and outward characteristics, though
generally (under moderate magnification) of a circular or sub-circular
shape. Their diameter varies from 15 miles or more to 3, and even less,
and their flanks rise much more steeply to the summit, which is seldom
very lofty, than those of the ring-plains, and fall more gradually to the
floor. There is no portion of the moon in which they do not abound,
whether it be on the ramparts, floors, and outer slopes of walled and
ring plains, the summits and escarpments of mountain ranges, amid the
intricacies of the highlands, or on the grey surface of the Maria. In
many instances they have a brighter and newer aspect than the larger
formations, often being the most brilliant points on their walls, when
they are found in this position. Very frequently too they are not only
very bright themselves, but stand on bright areas, whose borders are
generally concentric with them, which shine with a glistening lustre, and
form a kind of halo of light around them. Euclides and Bessarion A, and
the craters east of Landsberg, are especially interesting examples. It
seems not improbable that these areas may represent deposits formed by
some kind of matter ejected from the craters, but whether of ancient or
modern date, it is, of course, impossible to determine. Future observers
will perhaps be in a better position to decide the question without
cavil, if such eruptions should again take place. Like the larger
enclosures, these smaller objects frequently encroach upon each other--
crater-ring overlapping crater-ring, as in the case of Thebit, where a
large crater, which has interfered with the continuity of the east wall,
has, in its turn, been disturbed by a smaller crater on its own east
wall. The craters in many cases, possibly in the majority if we could
detect them, have central mountains, some of them being excellent tests
for telescopic definition--as, for example, the central peaks of
Hortensius, Bessarion, and that of the small crater just mentioned on the
east wall of Thebit A. A tendency to a linear arrangement is often
displayed, especially among the smaller class, as is also their
occurrence in pairs.
CRATER-CONES.--These objects, plentifully distributed on the lunar
surface, are especially interesting from their outward resemblance to the
parasitic cones found on the flanks of terrestrial volcanoes (Etna, for
instance). In the larger examples it is occasionally possible to see that
the interiors are either inverted cones without a floor, or cup-shaped
depressions on the summit of the object. Frequently, however, they are so
small that the orifice can only be detected under oblique illumination.
Under a high sun they generally appear as white spots, more or less ill-
defined, as on the floors of Archimedes, Fracastorius, Plato, and many
other formations, which include a great number, all of which are probably
crater cones, although only a few have been seen as such. It is a
significant fact that in these situations they are always found to be
closely associated with the light streaks which traverse the interior of
the formations, standing either on their surface or close to their edges.
The instrumental and meteorological requirements necessary for a
successful scrutiny of the smallest type of these features, are beyond
the reach of the ordinary observer in this country, as they demand direct
observation in large telescopes under the best atmospheric conditions.
Some years ago Dr. Klein of Cologne called attention to some very
interesting types of crater-cones, which may be found on certain dark or
smoky-grey areas on the moon. These, he considers, may probably represent
active volcanic vents, and urges that they should be diligently examined
and watched by observers who possess telescopes adequate to the task. The
most noteworthy examples of these objects are in the following
positions:--(1) West of a prominent ridge running from Beaumont to the
west side of Theophilus, and about midway between these formations; (2)
in the Mare Vaporum, south of Hyginus; (3) on the floor of Werner, near
the foot of the north wall; (4) under the east wall of Alphonsus, on the
dusky patch in the interior; (5) on the south side of the floor of Atlas.
I have frequently described elsewhere with considerable detail the
telescopic appearance of these features under various phases, and have
pointed out that though large apertures and high powers are needed to see
these cones to advantage, the dusky areas, easily traced on photograms,
might be usefully studied by observers with smaller instruments, as if
they represent the _ejecta_ from the crater-cones which stand upon them,
changes in their form and extent could very possibly be detected. In
addition to those already referred to, a number of mysterious dark spots
were discovered by Schmidt in the dusky region about midway between
Copernicus and Gambart, which Klein describes as perforated like a sieve
with minute craters. A short distance south-west of Copernicus stands a
bright crater-cone surrounded by a grey nimbus, which may be classed with
these objects. It is well seen under a high light, as indeed is the case
with most of these features.
CRATERLETS, CRATER-PITS.--To a great extent the former term is needless
and misleading, as the so-called craters merge by imperceptible
gradations into very minute objects, as small as half a mile in diameter,
and most probably, if we could more accurately estimate their size, still
less. The crater-pit, however, has well-marked peculiarities which
distinguish it from all other types, such as the absence of a
distinguishable rim and extreme shallowness. They appear to be most
numerous on the high-level plains and plateaus in the south-western
quadrant, and may be counted by hundreds under good atmospheric
conditions on the outer slopes of Walter, Clavius, and other large
enclosures. In these positions they are often so closely aggregated that,
as Nasmyth remarks, they remind one of an accumulation of froth. Even in
an 8 1/2 inch reflector I have frequently seen the outer slope of the
large ring-plain on the north-western side of Vendelinus, so perforated
with these objects that it resembled pumice or vesicular lava, many of
the little holes being evidently not circular, but square shaped and very
irregular. The interior of Stadius and the region outside abounds in
these minute features, but the well-known crater-row between this
formation and Copernicus seems rather to consist of a number of
inosculating crater-cones, as they stand very evidently on a raised bank
of some altitude.
MOUNTAIN RANGES, ISOLATED MOUNTAINS, &c.--The more massive and extended
mountain ranges of the moon are found in the northern hemisphere, and
(what is significant) in that portion of it which exhibits few
indications of other superficial disturbances. The most prominently
developed systems, the _Alps_, the _Caucasus_, and the _Apennines_,
forming a mighty western rampart to the Mare Imbrium and giving it all
the appearance of a vast walled plain, present few points of resemblance
to any terrestrial chain. The former include many hundred peaks, among
which, Mont Blanc rises to a height of 12,000 feet, and a second, some
distance west of Plato, to nearly as great an altitude; while others,
ranging from 5000 to 8000 feet, are common. They extend in a south-west
direction from Plato to the Caucasus, terminating somewhat abruptly, a
little west of the central meridian, in about N. lat. 42 deg. One of the
most interesting features associated with this range is the so-called
great Alpine valley, which cuts through it west of Plato. The _Caucasus_
consist of a massive wedge-shaped mountain land, projecting southwards,
and partially dividing the Mare Imbrium from the Mare Serenitatis, both
of which they flank. Though without peaks so lofty as those pertaining to
the Alps, there is one, immediately east of the ring-plain Calippus,
which, towering to 19,000 feet, surpasses any of which the latter system
can boast. The _Apennines_, however, are by far the most magnificent
range on the visible surface, including as they do some 3000 peaks, and
extending in an almost continuous curve of more than 400 miles in length
from Mount Hadley, on the north, to the fine ring-plain Eratosthenes,
which forms a fitting termination, on the south. The great headland Mount
Hadley rises more than 15,000 feet, while a neighbouring promontory on
the south-east of it is fully 14,000 feet, and another, close by, is
still higher above the Mare. Mount Huygens, again, in N. lat. 20 deg.,
and the square-shaped mass Mount Wolf, near the southern end of the
chain, include peaks standing 18,000 and 12,000 feet respectively above
the plain, to which their flanks descend with a steep declivity. The
counterscarp of the Apennines, in places 160 miles in width from east to
west, runs down to the Mare Vaporum with a comparatively gentle
inclination. It is everywhere traversed by winding valleys of a very
intricate type, all trending towards the south-west, and includes some
bright craters and mountain-rings. The _Carpathians_, forming in part the
southern border of the Mare Imbrium, extend for a length of more than 180
miles eastward of E., long. 16 deg., and, embracing the ring-plain Gay-
Lussac, terminate west of Mayer. They present a less definite front to
the Mare than the Apennines, and are broken up and divided by irregular
valleys and gaps; their loftiest peak, situated on a very projecting
promontory north-west of Mayer, rising to a height of 7000 feet.
Notwithstanding their comparatively low altitude, the region they occupy
forms a fine telescopic picture at lunar sunrise. The _Sinus Iridum
highlands_, bordering the beautiful bay on the north-east side of the
Mare Imbrium, rank among the loftiest and most intricate systems on the
moon, and, like the Apennines, present a steep face to the grey plain
from which they rise, though differing from them in other respects. They
include many high peaks, the loftiest, in the neighbourhood of the ring-
plain Sharp, rising 15,000 feet. There are probably some still higher
mountains in the vicinity, but the difficulties attending their
measurement render it impossible to determine their altitude with any
approach to accuracy.
_The Taurus Mountains_ extend from the west side of the Mare Serenitatis,
near Le Monnier and Littrow, in a north-westerly direction towards
Geminus and Berselius, bordering the west side of the Lacus Somniorum.
They are a far less remarkable system than any of the preceding, and
consist rather of a wild irregular mountain region than a range. In the
neighbourhood of Berselius are some peaks which, according to Neison,
cannot be less than 10,000 feet in height.
On the north side of the Mare Imbrium, east of Plato, there is a
beautiful narrow range of bright outlying heights, called the _Teneriffe
Mountains_, which include many isolated objects of considerable altitude,
one of the loftiest rising about 8000 feet. Farther towards the east lies
another group of a very similar character, called the _Straight Range_,
from its linear regularity. It extends from west to east for a distance
of about 60 miles, being a few miles shorter than the last, and includes
a peak of 6000 feet.
_The Harbinger Mountains_.--A remarkable group, north-west of
Aristarchus, including some peaks as high as 7000 feet, and other details
noticed in the catalogue.
The above comprise all the mountain ranges in the northern hemisphere of
any prominence, or which have received distinctive names, except the
_Hercynian Mountains_, on the north-east limb, east of the walled plain
Otto Struve. These are too near the edge to be well observed, but, from
what can be seen of them, they appear to abound in lofty peaks, and to
bear more resemblance to a terrestrial chain than any which have yet been
referred to.
The mountain systems of the southern hemisphere, except the ranges
visible on the limb, are far less imposing and remarkable than those just
described. The _Pyrenees_, on the western side of the Mare Nectaris,
extend in a meridional direction for nearly 190 miles, and include a peak
east of Guttemberg of nearly 12,000 feet, and are traversed in many
places by fine valleys.
_The Altai Mountains_ form a magnificent chain, 275 miles in length,
commencing on the outer eastern slope of Piccolomini, and following a
tolerably direct north-east course, with a few minor bendings, to the
west side of Fermat, where they turn more towards the north, ultimately
terminating about midway between Tacitus and Catherina. The region
situated on the south-east is a great table-land, without any prominent
features, rising gently towards the mountains, which shelve steeply down
to an equally barren expanse on the north-west, to which they present a
lofty face, having an average altitude of about 6000 feet. The loftiest
peak, over 13,000 feet, rises west of Fermat.
_The Riphaean Mountains_, a remarkably bright group, occupying an
isolated position in the Mare Procellarum south of Landsberg, and
extending for more than 100 miles in a meridional direction. They are
most closely aggregated at a point nearly due west of Euclides, from
which they throw off long-branching arms to the north and south, those on
the north bifurcating and gradually sinking to the level of the plain.
The loftiest peaks are near the extremity of this section, one of them
rising to 3000 feet. Two bright craters are associated with these
mountains, one nearly central, and the other south of it.
_The Percy Mountains_.--This name is given to the bright highlands
extending east of Gassendi towards Mersenius, forming the north-eastern
border of the Mare Humorum. They abound in minute detail--bright little
mountains and ridges--and include some clefts pertaining to the Mersenius
rill-system; but their most noteworthy feature is the long bright
mountain-arm, branching out from the eastern wall of Gassendi, and
extending for more than 50 miles towards the south-east.
The principal ranges on the limb are the _Leibnitz Mountains_, extending
from S. lat. 70 deg. on the west to S. lat. 80 deg. on the east limb.
They include some giant peaks and plateaus, noteworthy objects in
profile, some of which, according to Schroter and Madler, rise to 26,000
feet. The _Dorfel Mountains_, between S. lat. 80 deg. and 57 deg. on the
eastern limb, include, if Schroter's estimate is correct, three peaks
which exceed 26,000 feet. On the eastern limb, between S. lat. 35 deg.
and 18 deg., extend the _Rook Mountains_, which have peaks, according to
Schroter, as high as 25,000 feet. Next in order come the _Cordilleras_,
which extend to S. lat. 8 deg., and the _D'Alembert Mountains_, lying
east of Rocca and Grimaldi, closely associated with them, and probably
part of the same system. Some of the peaks approach 20,000 feet. In
addition to these mountain ranges there are others less prominent on the
limb in the northern hemisphere, which have not been named.
ISOLATED MOUNTAINS are very numerous in different parts of the moon, the
most remarkable are referred to in the appendix. Many remain unnamed.
CLEFTS OR RILLS.--Though Fontenelle, in his _Entretiens sur la Pluralite
des Mondes_, informs his pupil, the Marchioness, that "M. Cassini
discovered in the moon something which separates, then reunites, and
finally loses itself in a cavity, which from its appearance seemed to be
a river," it can hardly be supposed that what the French astronomer saw,
or fancied he saw, with the imperfect telescopes of that day, was one of
the remarkable and enigmatical furrows termed clefts or rills, first
detected by the Hanoverian selenographer Schroter; who, on October 7,
1787, discovered the very curious serpentine cleft near Herodotus, having
a few nights before noted for the first time the great Alpine valley west
of Plato, once classed with the clefts, though it is an object of a very
different kind. Between 1787 and 1797 Schroter found ten rills; but
twenty years elapsed before an addition was made to this number by the
discoveries of Gruithuisen, and, a short time after, by those of
Lohrmann, who in twelve months (1823-24) detected seventy. Kinau, Madler,
and finally Schmidt, followed, till, in 1866, when the latter published
his work, _Ueber Rillen auf dem Monde_, the list was thus summarised:--
In the 1st or N.W. quadrant 127 rills
In the 2nd or N.E. quadrant 75 rills
In the 3rd or S.E. quadrant 141 rills
In the 4th or S.W. quadrant 82 rills
or 425 in all. Since the date of this book the number of known rills has
been more than doubled; in fact, scarcely a lunation passes without new
discoveries being made.
The significance of the word _rille_ in German, a groove or furrow,
describes with considerable accuracy the usual appearance of the objects
to which it is applied, consisting as they do of long narrow channels,
with sides more or less steep, and sometimes vertical. They often extend
for hundreds of miles in approximately straight lines over portions of
the moon's surface, frequently traversing in their course ridges,
craters, and even more formidable obstacles, without any apparent check
or interruption, though their ends are sometimes marked by a mound or
crater. Their length ranges from ten or twelve to three hundred miles or
more (as in the great Sirsalis rill), their breadth, which is very
variable within certain limits, from less than half a mile to more than
two, and their depth (which must necessarily remain to a great extent
problematical) from 100 to 400 yards. They exhibit in the telescope a
gradation from somewhat coarse grooves, easily visible at suitable times
in very moderately sized instruments, to striae so delicate as to require
the largest and most perfect optical means and the best atmospheric
conditions to be glimpsed at all. Viewed under moderate amplification,
the majority of rills resemble deep canal-like channels with roughly
parallel sides, displaying occasionally local irregularities, and fining
off to invisibility at one or both ends. But, if critically scrutinised
in the best observing weather with high powers, the apparent evenness of
their edges entirely disappears, and we find that the latter exhibit
indentations, projections, and little flexures, like the banks of an
ordinary stream or rivulet, or, to use a very homely simile, the serrated
edges and little jagged irregularities of a biscuit broken across. In
some cases we remark crateriform hollows or sudden expansions in their
course, and deep sinuous ravines, which render them still more
unsymmetrical and variable in breadth. With regard to their distribution
on the lunar surface; they are found in almost every region, but perhaps
not so frequently on the surface of the Maria as elsewhere, though, as in
the case of the Triesnecker and other systems, they often abound in the
neighbourhood of disturbed regions in these plains, and in many cases
along their margins, as, for example, the Gassendi-Mersenius and the
Sabine-Ritter groups. The interior of walled plains are frequently
intersected by them, as in Gassendi, where nearly forty, more or less
delicate examples, have been seen; in Hevel, where there is a very
interesting system of crossed clefts, and within Posidonius. If we study
any good modern lunar map, it is evident how constantly they appear near
the borders of mountain ranges, walled-plains, and ring-plains; as, for
instance, at the foot of the Apennines; near Archimedes, Aristarchus,
Ramsden, and in many other similar positions. Rugged highlands also are
often traversed by them, as in the case of those lying west of Le Monnier
and Chacornac, and in the region west of the Mare Humorum. It may be here
remarked, however, as a notable fact, that the neighbourhood of the
grandest ring-mountain on the moon, Copernicus, is, strange to say,
devoid of any features which can be classed as true clefts, though it
abounds in crater-rows. The intricate network of rills on the west of
Triesnecker, when observed with a low power, reminds one of the wrinkles
on the rind of an orange or on the skin of a withered apple. Gruithuisen,
describing the rill-traversed region between Agrippa and Hyginus, says
that "it has quite the look of a Dutch canal map." In the subjoined
catalogue many detailed examples will be given relating to the course of
these mysterious furrows; how they occasionally traverse mountain arms,
cut through, either completely or partially (as in Ramsden), the borders
of ring-plains and other enclosures, while not unfrequently a small mound
or similar feature appears to have caused them to swerve suddenly from
their path, as in the case of the Ariadaeus cleft, and in that of one
member of the Mercator-Campanus system.
Of the actual nature of the lunar rills we are, it must be confessed,
supremely ignorant. With some of the early observers it was a very
favourite notion that they are artificial works, constructed presumably
by Kepler's _sub-volvani_, or by other intelligences. There is perhaps
some excuse to be made for the freaks of an exuberant fancy in regard to
objects which, if we ignore for a moment their enormous dimensions,
judged by a terrestrial standard, certainly have, in their apparent
absence of any physical relation to neighbouring objects, all the
appearance of being works of art rather than of nature. The keen-sighted
and very imaginative Gruithuisen believed that in some instances they
represent roads cut through interminable forests, and in others the
dried-up beds of once mighty rivers. His description of the Triesnecker
rill-system reads like a page from a geographical primer. A portion of it
is compared to the river Po, and he traces its course mile by mile up to
the "delta" at its place of disemboguement into the Mare Vaporum. From
the position of some rills with respect to the contour of the surrounding
country, it is evident that if water were now present on the moon, they,
being situated at the lowest level, would form natural channels for its
reception; but the exceptions to this arrangement are so numerous and
obvious, that the idea may be at once dismissed that there is any analogy
between them and our rivers. The eminent selenographer, the late W.K.
Birt, compared many of them to "inverted river-beds" from the fact that,
as often as not, they become broader and deeper as they attain a higher
level. The branches resemble rivers more frequently than the main
channels; for they generally commence as very fine grooves, and, becoming
broader and broader, join them at an acute angle. An attempt again has
been made to compare the lunar clefts with those vast gorges, the
marvellous results of aqueous action, called canyons, which attain their
greatest dimensions in North America; such as the Great Canyon of the
Colorado, which is at least 300 miles in length, and in places 2000 yards
in depth, with perpendicular or even overhanging sides; but the analogy,
at first sight specious, utterly breaks down under closer examination.
Some selenographers consider them to consist of long-extending rows of
confluent craters, too minute to be separately distinguished, and to be
thus due to some kind of volcanic action. This is undoubtedly true in
many instances, for almost every lunar region affords examples of crater-
rows merging by almost imperceptible gradations into cleft-like features,
and crater-rows of considerable size resemble clefts under low powers.
Still it seems probable that the greater number of these features are
immense furrows or cracks in the surface and nothing more; for the higher
the magnifying power employed in their examination, the less reason there
is to object to this description. Dr. Klein of Cologne believes that
rills of this class are due to the shrinkage of parts of the moon's
crust, and that they are not as a rule the result of volcanic causes,
though he admits that there may be some which have a seismic origin. No
good reason has as yet been given for the fact that they so frequently
cross small craters and other objects in their course, though it has been
suggested that the route followed by a rill from crater to crater in
these instances may be a line of least surface resistance, an explanation
far from being satisfactory.
Whether variations in the visibility of lunar details, when observed
under apparently similar conditions, actually occur from time to time
from some unknown cause, is one of those vexed questions which will only
be determined when the moon is systematically studied by experienced
observers using the finest instruments at exceptionally good stations;
but no one who examines existing records of observations of rills by
Gruithuisen, Lohrmann, Madler, Schmidt, and other observers, can well
avoid the conclusion that the anomalies brought to light therein point
strongly to the probability of the existence of some agency which
occasionally modifies their appearance or entirely conceals them from
view.
The following is one illustration out of many which might be quoted. At a
point in its course, nearly due north of the ring-plain Agrippa, the
great Ariadaeus cleft sends out a branch which runs into the well-known
Hyginus cleft, reminding one, as Dr. Klein remarks, of two rivers
connected in the shortest way by a canal. This uniting furrow was
detected by Gruithuisen, who observed it several times. On some occasions
it appeared perfectly straight, at others very irregular; but, what is
very remarkable, although two such accurate observers as Lohrmann and
Madler frequently scrutinised the region, neither of them saw a trace of
this object; and but for its rediscovery by Schmidt in 1862, its
existence would certainly have been ignored by selenographers as a mere
figment of Gruithuisen's too lively imagination. Dr. Klein has frequently
seen this rill with great distinctness, and at other times sought for it
in vain; though on each occasion the conditions of illumination,
libration, and definition were practically similar. I have sometimes
found this cleft an easy object with a 4 inch achromatic. Again, many
rills described by Madler as very delicate and difficult to trace, may
now be easily followed in "common telescopes." In short, the more direct
telescopic observations accumulate, and the more the study of minute
detail is extended, the stronger becomes the conviction, that in spite of
the absence of an appreciable atmosphere, there may be something
resembling low-lying exhalations from some parts of the surface which
from time to time are sufficiently dense to obscure, or even obliterate,
the region beneath them.
If, as seems most probable, these gigantic cracks are due to contractions
of the moon's surface, it is not impossible, in spite of the assertions
of the text-books to the effect that our satellite is now "a changeless
world," that emanations may proceed from these fissures, even if, under
the monthly alternations of extreme temperatures, surface changes do not
now occasionally take place from this cause also. Should this be so, the
appearance of new rills and the extension and modification of those
already existing may reasonably be looked for. Many instances might be
adduced tending to confirm this supposition, to one of which, as coming
under my notice, I will briefly refer. On the evening of November 11,
1883, when examining the interior of the great ring-plain Mersenius with
a power of 350 on an 8 1/2 inch reflector; in addition to the two closely
parallel clefts discovered by Schmidt, running from the inner foot of the
north-eastern rampart towards the centre, I remarked another distinct
cleft crossing the northern part of the floor from side to side. Shortly
afterwards, M. Gaudibert, one of our most experienced selenographers, who
has discovered many hitherto unrecorded clefts, having seen my drawing,
searched for this object, and, though the night was far from favourable,
had distinct though brief glimpses of it with the moderate magnifying
power of 100. Mersenius is a formation about 40 miles in diameter, with a
prominently convex interior, containing much detail which has received
more than ordinary attention from observers. It has, moreover, been
specially mapped by Schmidt and others, yet no trace of this rill was
noted, though objects much more minute and difficult have not been
overlooked. Does not an instance of this kind raise a well-grounded
suspicion of recent change which it is difficult to explain away?
To see the lunar clefts to the best advantage, they must be looked for
when not very far removed from the terminator, as when so situated the
black shadow of one side, contrasted with the usually brightly-
illuminated opposite flank, renders them more conspicuous than when they
are viewed under a higher sun. Though, as a rule, invisible at full moon,
some of the coarser clefts--as, for example, a portion of the Hyginus
furrow, and that north of Birt--may be traced as delicate white lines
under a nearly vertical light.
For properly observing these objects, a power of not less than 300 on
telescopes of large aperture is needed; and in studying their minute and
delicate details, we are perhaps more dependent on atmospheric conditions
than in following up any other branch of observational astronomy. Few
indeed are the nights, in our climate at any rate, when the rough,
irregular character of the steep interior of even the coarser examples of
these immense chasms can be steadily seen. We can only hope to obtain a
more perfect insight into their actual structural peculiarities when they
are scrutinised under more perfect climatic circumstances than they have
been hitherto. When observing the Hyginus cleft, Dr. Klein noticed that
at one place the declivities of the interior displayed decided
differences of tint. At many points the reflected sunlight was of a
distinctly yellow hue, while in other places it was white, as if the
cliffs were covered with snow. He compares this portion of the rill to
the Rhine valley between Bingen and Coblentz, but adds that the latter,
if viewed from the moon, would probably not present so fresh an
appearance, and would, of course, be frequently obscured by clouds.
Since the erection of the great Lick telescope on Mount Hamilton, our
knowledge of the details of some of the lunar clefts has been greatly
increased, as in the case of the Ariadaeus cleft, and many others.
Professor W.H. Pickering, also, at Arequipa, has made at that ideal
astronomical site many observations which, when published, will throw
more light upon their peculiar characteristics.
A few years ago M.E.L. Trouvelot of Meudon drew attention to a curious
appearance which he noted in connection with certain rills when near the
terminator, viz., extremely attenuated threads of light on their sites
and their apparent prolongations. He observed it in the ring-plain
Eudoxus, crossing the southern side of the floor from wall to wall; and
also in connection with the prominent cleft running from the north side
of Burg to the west of Alexander, and in some other situations. He terms
these phenomena _Murs enigmatiques_. Apparent prolongations of clefts in
the form of rows of hillocks or small mounds are very common.
FAULTS.--These sudden drops in the surface, representing local
dislocations, are far from unusual: the best examples being the straight
wall, or "railroad," west of Birt; that which strikes obliquely across
Plato; another which traverses Phocylides; and a fourth that has
manifestly modified the mountain arm north of Cichus. They differ from
the terrestrial phenomena so designated in the fact that the surface
indications of these are destroyed by denudation or masked by deposits of
subsequent date. In many cases on the moon, though its course cannot be
traced in its entirety by its shadow, yet the existence of a fault may be
inferred by the displacement and fracture of neighbouring objects.
VALLEYS.--Features thus designated, differing greatly both in size and
character, are met with in almost every part of the surface, except on
the grey plains. While the smallest examples, from their delicacy,
tenuity, and superficial resemblance to rills, are termed rill-valleys,
the larger and more conspicuous assume the appearance of coarse chasms,
gorges, or trough-like depressions. Between these two extremes, are many
objects of moderate dimensions--winding or straight ravines and defiles
bounded by steep mountains, and shallow dales flanked by low rounded
heights. The rill valleys are very numerous, only differing in many
instances from the true rills in size, and are probably due to the same
cause. Among the most noteworthy valleys of the largest class must, of
course, be placed the great valley of the Alps, one of the most striking
objects in the northern hemisphere, which also includes the great valley
south-east of Ukert. The Rheita valley, the very similar chasm west of
Reichenbach, and the gorge west of Herschel, are also notable examples in
the southern hemisphere. The borders of some of the Maria (especially
that of the Mare Crisium) and of many of the depressed rimless
formations, furnish instances of winding valleys intersecting their
borders: the hilly regions likewise often abound in long branching
defiles.
BRIGHT RAY-SYSTEMS.--Reference has already been made to the faint light
streaks and markings often found on the floors of the ring-mountains and
in other situations, and to the brilliant _nimbi_ surrounding some of the
smaller craters; but, in addition to these, many objects on the moon's
visible surface are associated with a much more remarkable and
conspicuous phenomenon--the bright rays which, under a high sun, are seen
either to radiate from them as apparent centres to great distances, or,
in the form of irregular light areas, to environ them, and to throw out
wide-spreading lucid beams, extending occasionally many hundreds of miles
from their origin. The more striking of these systems were recognised and
drawn at a very early stage of telescopic observation, as may be seen if
we consult the quaint old charts of Hevel, Riccioli, Fontana, and other
observers of the seventeenth century, where they are always prominently,
though very inaccurately, portrayed. The principal ray-systems are those
of Tycho, Copernicus, Kepler, Anaxagoras, Aristarchus, Olbers, Byrgius A,
and Zuchius; while Autolycus, Aristillus, Proclus, Timocharis, Furnerius
A, and Menelaus are grouped as constituting minor systems. Many
additional centres exist, a list of which will be found in the appendix.
The rays emanating from Tycho surpass in extent and interest any of the
others. Hundreds of distinct light streaks originate round the grey
margin of this magnificent object, some of them extending over a greater
part of the moon's visible superficies, and "radiating," in the words of
Professor Phillips, "like false meridians, or like meridians true to an
earlier pole of rotation." No systematic attempt has yet been made to map
them accurately as a whole on a large scale, for their extreme intricacy
and delicacy would render the task a very difficult one, and, moreover,
would demand a long course of observation with a powerful telescope in an
ideal situation; but Professor W.H. Pickering, observing under these
conditions at Arequipa, has recently devoted considerable attention both
to the Tycho and other rays, with especially suggestive and important
results, which may be briefly summarised as follows:--
(1.) That the Tycho streaks do not radiate from the apparent centre of
this formation, but point towards a multitude of minute craterlets on its
south-eastern or northern rims. Similar craterlets occur on the rims of
other great craters, forming ray-centres.
(2.) Speaking generally, a very minute and brilliant crater is located at
the end of the streak nearest the radiant point, the streak spreading out
and becoming fainter towards the other end. The majority of the streaks
appear to issue from one or more of these minute craters, which rarely
exceed a mile in diameter.
(3.) The streaks which do not issue from minute craters, usually lie upon
or across ridges, or in other similar exposed situations, sometimes
apparently coming through notches in the mountain walls.
(4.) Many of the Copernicus streaks start from craterlets within the rim,
flow up the inside and down the outside of the walls. Kepler includes two
such craterlets, but here the flow seems to have been more uniform over
the edges of the whole crater, and is not distinctly divided up into
separate streams.
(5.) Though there are similar craters within Tycho, the streaks from them
do not extend far beyond the walls. All the conspicuous Tycho streaks
originate outside the rim.
(6.) The streaks of Copernicus, Kepler, and Aristarchus are greyish in
colour, and much less white than those associated with Tycho: some white
lines extending south-east from Aristarchus do not apparently belong to
the system. In the case of craterlets lying between Aristarchus and
Copernicus the streaks point away from the latter.
(7.) There are no very long streaks; they vary from ten to fifty miles in
length, and are rarely more than a quarter of a mile broad at the crater.
From this point they gradually widen out and become fainter. Their width,
however, at the end farthest from the crater, seldom exceeds five miles.
These statements, especially those relating to the length of the streaks,
are utterly opposed to prevailing notions, but Professor Pickering
specifies the case of the two familiar parallel rays extending from the
north-east of Tycho to the region east of Bullialdus. His observations
show that these streaks, originating at a number of little craters
situated from thirty to sixty miles beyond the confines of Tycho, "enter
a couple of broad slightly depressed valleys. In these valleys are found
numerous minute craters of the kind above described, with intensely
brilliant interiors. When the streaks issuing from those craters near
Tycho are nearly exhausted, they are reinforced by streaks from other
craters which they encounter upon the way, the streaks becoming more
pronounced at these points. These streaks are again reinforced farther
out. These parallel rays must therefore not be considered as two streaks,
but as two series of streaks, the components of which are placed end to
end."
Thus, according to Professor Pickering, we must no longer regard the rays
emanating from the Tycho region and other centres as continuous, but as
consisting of a succession of short lengths, diminishing in brilliancy
but increasing in width, till they reach the next crater lying in their
direction, when they are reinforced; and the same process of gradual
diminution in brightness and reinforcement goes on from one end to the
other.
The following explanation is suggested to account for the origin of the
rays:--"The earth and her satellite may differ not so much as regards
volcanic action as in the densities of their atmospheres. Thus if the
craterlets on the rim of Tycho were constantly giving out large
quantities of gas or steam, which in other regions was being constantly
absorbed or condensed, we should have a wind uniformly blowing away from
that summit in all directions. Should other summits in its vicinity
occasionally give out gases, mixed with any fine white powder, such as
pumice, this powder would be carried away from Tycho, forming streaks."
The difficulty surrounding this very ingenious hypothesis is, that
though, assuming the existence of pumice-emitting craters and regions of
condensation, there might be a more or less lineal and streaky deposition
of this white material over large areas of the moon, why should this
deposit be so definitely arranged, and why should these active little
craters happen to lie on these particular lines?
The confused network of streaks round Copernicus seem to respond more
happily to the requirements of Professor Pickering's hypothesis, for here
there is an absence of that definiteness of direction so manifestly
displayed in the case of the Tycho rays, and we can well imagine that
with an area of condensation surrounding this magnificent object beyond
the limits of the streaks, and a number of active little craters on and
about its rim, the white material ejected might be drawn outwards in
every direction by wind currents, which possibly once existed, and,
settling down, assume forms such as we see.
Nasmyth's well-known hypothesis attributes the radiating streaks to
cracks in the lunar globe caused by the action of an upheaving force, and
accounts for their whiteness by the outwelling of lava from them which
has spread to a greater or less distance on either side. If the moon has
been fractured in this way, we can easily suppose that the craters formed
on these fissures, being in communication with the interior, might eject
some pulverulent white matter long after the rest of the surface with its
other types of craters had attained a quiescent stage.
The Tycho rays, when viewed under ordinary conditions, appear to extend
in unbroken bands to immense distances. One of the most remarkable,
strikes along the eastern side of Fracastorius, across the Mare Nectaris
to Guttemberg, while another, more central, extends, with local
variations in brightness, through Menelaus, over the Mare Serenitatis
nearly to the north-west limb. This is the ray that figures so
prominently in rude woodcuts of the moon, in which the Mare Serenitatis
traversed by it is made to resemble the Greek letter PHI. The Kepler,
Aristarchus, and Copernicus systems, though of much smaller extent, are
very noteworthy from the crossing and apparent interference of the rays;
while those near Byrgius, round Aristarchus, and the rays from Proclus,
are equally remarkable.
[Nichol found that the rays from Kepler cut through rays from Copernicus
and Aristarchus, while rays from the latter cut through rays from the
former. He therefore inferred that their relative ages stand in the
order,--Copernicus, Aristarchus, Kepler.]
As no branch of selenography has been more neglected than the observation
of these interesting but enigmatical features, one may hope that, in
spite of the exacting conditions as to situation and instrumental
requirements necessary for their successful scrutiny, the fairly equipped
amateur in this less favoured country will not be deterred from
attempting to clear up some of the doubts and difficulties which at
present exist as to their actual nature.
THE MOON'S ALBEDO, SURFACE BRIGHTNESS, &c.--Sir John Herschel maintained
that "the actual illumination of the lunar surface is not much superior
to that of weathered sandstone rock in full sunshine." "I have," he says,
"frequently compared the moon setting behind the grey perpendicular
facade of the Table Mountain, illuminated by the sun just risen in the
opposite quarter of the horizon, when it has been scarcely
distinguishable in brightness from the rock in contact with it. The sun
and moon being at nearly equal altitudes, and the atmosphere perfectly
free from cloud or vapour, its effect is alike on both luminaries."
Zollner's elaborate researches on this question are closely in accord
with the above observational result. Though he considers that the
brightest parts of the surface are as white as the whitest objects with
which we are acquainted, yet, taking the reflected light as a whole, he
finds that the moon is more nearly black than white. The most brilliant
object on the surface is the central peak of the ring-plain Aristarchus,
the darkest the floor of Grimaldi, or perhaps a portion of that of the
neighbouring Riccioli. Between these extremes, there is every gradation
of tone. Proctor, discussing this question on the basis of Zollner's
experiments respecting the light reflected by various substances,
concludes that the dark area just mentioned must be notably darker than
the dark grey syenite which figures in his tables, while the floor of
Aristarchus is as white as newly fallen snow.
The estimation of lunar tints in the usual way, by eye observations at
the telescope, involving as it does physiological errors which cannot be
eliminated, is a method far too crude and ambiguous to form the basis of
a scientific scale or for the detection of slight variations. An
instrument on the principle of Dawes' solar eyepiece has been suggested;
this, if used with an invariable and absolute scale of tints, would
remove many difficulties attending these investigations. The scale which
was adopted by Schroter, and which has been used by selenographers up to
the present time, is as follows:--
0 deg. = Black.
1 deg. = Greyish black.
2 deg. = Dark grey.
3 deg. = Medium grey.
4 deg. = Yellowish grey.
5 deg. = Pure light grey.
6 deg. = Light whitish grey.
7 deg. = Greyish white.
8 deg. = Pure white.
9 deg. = Glittering white.
10 deg. = Dazzling white.
The following is a list of lunar objects published in the
_Selenographical Journal_, classed in accordance with this scale:--
0 deg. Black shadows.
1 deg. Darkest portions of the floors of Grimaldi and Riccioli.
1 1/2 deg. Interiors of Boscovich, Billy, and Zupus.
2 deg. Floors of Endymion, Le Monnier, Julius Caesar, Cruger, and
Fourier _a_.
2 1/2 deg. Interiors of Azout, Vitruvius, Pitatus, Hippalus, and Marius.
3 deg. Interiors of Taruntius, Plinius, Theophilus, Parrot,
Flamsteed, and Mercator.
3 1/2 deg. Interiors of Hansen, Archimedes, and Mersenius.
4 deg. Interiors of Manilius, Ptolemaeus, and Guerike.
4 1/2 deg. Surface round Aristillus, Sinus Medii.
5 deg. Walls of Arago, Landsberg, and Bullialdus. Surface round
Kepler and Archimedes.
5 1/2 deg. Walls of Picard and Timocharis. Rays from Copernicus.
6 deg. Walls of Macrobius, Kant, Bessel, Mosting, and Flamsteed.
6 1/2 deg. Walls of Langrenus, Theaetetus, and Lahire.
7 deg. Theon, Ariadaeus, Bode B, Wichmann, and Kepler.
7 1/2 deg. Ukert, Hortensius, Euclides.
8 deg. Walls of Godin, Bode, and Copernicus.
8 1/2 deg. Walls of Proclus, Bode A, and Hipparchus c.
9 deg. Censorinus, Dionysius, Mosting A, and Mersenius B and c.
9 1/2 deg. Interior of Aristarchus, La Peyrouse DELTA.
10 deg. Central peak of Aristarchus.
TEMPERATURE OF THE MOON'S SURFACE.--Till the subject was undertaken some
years ago by Lord Rosse, no approach was made to a satisfactory
determination of the surface temperature of the moon. From his
experiments he inferred that the maximum temperature attained, at or near
the equator, about three days after full moon, does not exceed 200 deg.
C., while the minimum is not much under zero C. Subsequent experiments,
however, both by himself and Professor Langley, render these results more
than doubtful, without it is admitted that the moon has an atmospheric
covering. Langley's results make it probable that the temperature never
rises above the freezing-point of water, and that at the end of the
prolonged lunar night of fourteen days it must sink to at least 200 deg.
below zero. Mr. F.W. Verey of the Alleghany Observatory has recently
conducted, by means of the bolometer, similar researches as to the
distribution of the moon's heat and its variation with the phase, by
which he has deduced the varying radiation from the surface in different
localities of the moon under various solar altitudes.
LUNAR OBSERVATION.--In observing the moon, we enjoy an advantage of which
we cannot boast when most other planetary bodies are scrutinised; for we
see the actual surface of another world undimmed by palpable clouds or
exhalations, except such as exist in the air above us; and can gaze on
the marvellous variety of objects it presents much as we contemplate a
relief map of our own globe. But inasmuch as the manifold details of the
relief map require to be placed in a certain light to be seen to the best
advantage, so the ring-mountains, rugged highlands, and wide-extending
plains of our satellite, as they pass in review under the sun, must be
observed when suitable conditions of illumination prevail, if we wish to
appreciate their true character and significance.
As a general rule, lunar objects are best seen when they are at no great
distance from "the terminator," or the line dividing the illumined from
the unillumined portion of the spherical surface. This line is constantly
changing its position with the sun, advancing slowly onwards towards the
east at a rate which, roughly speaking, amounts to about 30.5 min. in an
hour, or passing over 10 deg. of lunar longitude in about 19 hrs. 40
mins. When an object is situated on this line, the sun is either rising
or setting on the neighbouring region, and every inequality of the
surface is rendered prominent by its shadow; so that trifling variations
in level and minor asperities assume for the time being an importance to
which they have no claim. If we are observing an object at lunar sunrise,
a very short time, often only a few minutes, elapses before the confusion
caused by the presence of the shadows of these generally unimportant
features ceases to interfere with the observation, and we can distinguish
between those details which are really noteworthy and others which are
trivial and evanescent. Every formation we are studying should be
observed, and drawn if possible, under many different conditions of
illumination. It ought, in fact, to be examined from the time when its
loftiest heights are first illumined by the rising sun till they
disappear at sunset. This is, of course, practically impossible in the
course of one lunation, but by utilising available opportunities, a
number of observations may be obtained under various phases which will be
more or less exhaustive. It cannot be said that much is known about any
object until an attempt has been made to carry out this plan. Features
which assume a certain appearance at one phase frequently turn out to be
altogether different when viewed under another; important details
obscured by shadows, craters masked by those of neighbouring objects, or
by the shadows of their own rims, are often only revealed when the sun
has attained an altitude of ten degrees or more. In short, there is
scarcely a formation on the moon which does not exemplify the necessity
of noting its aspect from sunrise to sunset. Regard must also be had to
libration, which affects to a greater or less degree every object;
carrying out of the range of observation regions near the limb at one
time, and at another bringing into view others beyond the limits of the
maps, which represent the moon in the mean state of libration. The area,
in fact, thus brought into view, or taken out of it, is between 1/12th
and 1/13th of the entire area of the moon, or about the 1/6th part of the
hemisphere turned away from the earth. It is convenient to bear in mind
that we see an object under nearly the same conditions every 59 d. 1 h.
28 m., or still more accurately, after the lapse of fifteen lunations, or
442 d. 23 h. Many observers avoid the observation of objects under a high
light. This, however, should never be neglected when practicable, though
in some cases it is not easy to carry out, owing to the difficulty in
tracing details under these circumstances.
Although to observe successfully the minuter features, such as the rills
and the smaller craterlets, requires instruments of large aperture
located in favourable situations, yet work of permanent value may be
accomplished with comparatively humble telescopic means. A 4 inch
achromatic, or a silver-on-glass reflector of 6 or 6 1/2 inches aperture,
will reveal on a good night many details which have not yet been
recorded, and the possessor of instruments of this size will not be long
in discovering that the moon, despite of what is often said, has not been
so exhaustively surveyed that nothing remains for him to do.
Only experience and actual trial will teach the observer to choose the
particular eyepiece suitable for a given night or a given object. It will
be found that it is only on very rare occasions that he can accomplish
much with powers which, perhaps only on two or three nights in a year in
this climate, tell to great advantage; though it sometimes happens that
the employment of an eyepiece, otherwise unsuitable for the night, will,
during a short spell of good definition, afford a fleeting glimpse of
some difficult feature, and thus solve a doubtful point. It has often
been said that the efficiency of a telescope depends to a great extent on
"the man at the eye end." This is as true in the case of the moon as it
is in other branches of observational astronomy.
Observers, especially beginners, frequently fall into great error in
failing to appreciate the true character of what they see. In this way a
shallow surface depression, possibly only a few feet below the general
level of the neighbouring country, is often described as a "vast gorge,"
because, under very oblique light, it is filled with black shadow; or an
insignificant hillock is magnified into a mountain when similarly viewed.
Hence the importance, just insisted on, of studying lunar features under
as many conditions as possible before finally attempting to describe
them.
However indifferent a draughtsman an observer may be, if he endeavours to
portray what he sees to the best of his ability, he will ultimately
attain sufficient skill to make his work useful for future reference: in
any case, it will be of more value than a mere verbal description without
a sketch. Doubt and uncertainty invariably attend to a greater or less
extent written notes unaccompanied by drawings, as some recent
controversies, respecting changes in Linne and elsewhere, testify. Now
that photographs are generally available to form the basis of a more
complete sketch, much of the difficulty formerly attending the correct
representation of the outline and grosser features of a formation has
been removed, and the observer can devote his time and attention to the
insertion and description of less obvious objects.
PROGRESS OF SELENOGRAPHY.--Till within recent years, the systematic study
of the lunar surface may be said to have been confined, in this country
at any rate, to a very limited number of observers, and, except in rare
instances, those who possessed astronomical telescopes only directed them
to the moon as a show object to excite the wonder of casual visitors. The
publication of Webb's "Celestial Objects" in 1859, the supposed physical
change in the crater Linne, announced in 1866, and the appearance of an
unrecorded black spot near Hyginus some ten years later, had the effect
of awakening a more lively interest in selenography, and undoubtedly
combined to bring about a change in this respect, which ultimately
resulted in the number of amateurs devoting much of their time to this
branch of observational astronomy being notably increased. Still, large
telescopes, as a rule, held aloof for some unexplained reason, or were
only employed in a desultory and spasmodic fashion, without any very
definite object. When the Council of the British Association for the
Advancement of Science, stimulated by the Linne controversy, deemed the
moon to be worthy of passing attention, observations, directed to objects
suspected of change (the phenomena on the floor of Plato) were left to
three or four observers, under the able direction of Mr. Birt, the
largest instruments available being an 8 1/4 inch reflector and the
Crossley refractor of 9 inches aperture! During the last decade, however,
all this has been changed, and we not only have societies, such as the
British Astronomical Association, setting apart a distinct section for
the systematic investigation of lunar detail, but some of the largest and
most perfect instruments in the world, among them the noble refractor on
Mount Hamilton, employed in photographing the moon or in scrutinising her
manifold features by direct observation. Hence, it may be said that
selenography has taken a new and more promising departure, which, among
other results, must lead to a more accurate knowledge of lunar
topography, and settle possibly, ere long, the vexed question of change,
without any residuum of doubt.
Lunar photography as exemplified by the marvellous and beautiful pictures
produced at the Lick Observatory under the auspices of Dr. Holden, and
the exquisite enlargements of them by Dr. Weinek of Prague; at Paris by
the brothers Henry; and at Brussels by M. Prinz; point to the not far
distant time when we shall possess complete photographic maps on a large
scale of the whole visible disc under various phases of illumination,
which will be of inestimable value as topographical charts. When this is
accomplished, the observer will have at his command faithful
representations of any formation, or of any given region he may require,
to utilise for the study of the smaller details by direct observation.
Desultory and objectless drawings and notes have hitherto been more or
less characteristic of the work done, even by those who have given more
than ordinary attention to the moon. Though these, if duly recorded, are
valuable as illustrating the physical structure, the estimated brightness
under various phases, and other peculiarities of lunar features, they do
not materially forward investigations relating to the discovery of
present lunar activity or to the detection of actual change. It is
reiterated _ad nauseam_ in many popular books that the moon is a
changeless world, and it is implied that, having attained a state when no
further manifestations of internal or external forces are possible, it
revolves round the earth in the condition, for the most part, of a
globular mass of vesicular lava or slag, possessing no interest except as
a notable example of a "burnt-out planet." In answer to these dogmatic
assertions, it may be said that, notwithstanding the multiplication of
monographs and photographs, the knowledge we possess, even of the larger
and more prominent objects, is far too slight to justify us in
maintaining that changes, which on earth we should use a strong adjective
to describe, have not taken place in connection with some of them in
recent years. Would the most assiduous observer assert that his knowledge
of any one of the great formations, in the south-west quadrant, for
example, is so complete that, if a chasm as big as the Val del Bove was
blown out from its flanks, or formed by a landslip, he would detect the
change in the appearance of an area (some three miles by four) thus
brought about, unless he had previously made a very prolonged and
exhaustive study of the object? Or, again, among formations of a
different class, the craters and crater-cones; might not objects as large
as Monte Nuovo or Jorullo come into existence in many regions without any
one being the wiser? It would certainly have needed a persistent lunar
astronomer, and one furnished with a very perfect telescope, to have
noted the changes that have occurred within the old crater-ring of Somma
or among the Santorin group during the past thirty years, or even to have
detected the effects resulting from the great catastrophe in A.D. 79, at
Vesuvius; yet these objects are no larger than many which, if they were
situated on our satellite, would be termed comparatively small, if not
insignificant.
One of the principal aims of lunar research is to learn as much as
possible as to the present condition of the surface. Every one qualified
to give an opinion will admit that this cannot be accomplished by roaming
at large over the whole visible superficies, but only by confining
attention to selected areas of limited extent, and recording and
describing every object visible thereon, under various conditions of
illumination, with the greatest accuracy attainable. This plan was
suggested and inaugurated nearly thirty years ago by Mr. Birt, under the
patronage of the British Association; but as he proposed to deal with the
entire disc in this way, the magnitude and ambitious character of the
scheme soon damped the ardour of those who at first supported it, and it
was ultimately abandoned. It was, however, based on the only feasible
principle which, as it seems to the writer, will not result in doubt and
confusion. Now that photography has come to the assistance of the
observer, Mr. Birt's proposal, if confined within narrower limits, would
be far less arduous an undertaking than before, and might be easily
carried out. A complete photographic survey of a few selected regions, as
a basis for an equally thorough and exhaustive scrutiny by direct
observation, would, it is believed, lead to a much more satisfactory and
hopeful method for ultimately furnishing irrefragable testimony as to
permanency or change than any that has yet been undertaken.
CATALOGUE OF LUNAR FORMATIONS
FIRST QUADRANT
WEST LONGITUDE 90 deg. TO 60 deg.
SCHUBERT.--This ring-plain, about 46 miles in diameter, situated on the
N.E. side of the Mare Smythii, is too near the limb to be well observed.
NEPER.--Though still nearer the limb, this walled-plain, 74 miles in
diameter, is a much more conspicuous object. It has a lofty border and a
prominent central mountain, the highest portion of a range of hills which
traverses the interior from N. to S.
APOLLONIUS.--A ring-plain, 30 miles in diameter, standing in the
mountainous region S. of the Mare Crisium. There is a large crater on the
S.W. wall, and another, somewhat smaller, adjoining it on the N. There
are many brilliant craters in the vicinity.
FIRMICUS.--A somewhat larger, more regular, but, in other respects, very
similar ring-plain, N.W. of the last. Some distance on the W., Madler
noted a number of dark-grey streaks which apparently undergo periodical
changes, suggestive of something akin to vegetation. They are situated
near a prominent mountain situated in a level region.
AZOUT.--A small ring-plain, connected with the last by a lofty ridge. It
is the apparent centre of many other ridges and valleys which radiate
from it towards the N.W. and the Mare Crisium. There is a central
mountain, not an easy telescopic object, on its dusky floor.
CONDORCET.--A very prominent ring-plain, 45 miles in diameter, situated
on the mountainous S.W. margin of the Mare Crisium. It is encircled by a
lofty wall about 8000 feet in height. The dark interior of this and of
the three preceding formations render them easily traceable under a high
angle of illumination.
HANSEN.--A ring-plain, 32 miles in diameter, on the W. border of the Mare
Crisium N. of Condorcet. Schmidt shows a central mountain and a terraced
wall.
ALHAZEN.--This ring-plain, rather smaller than the last, is the most
northerly of the linear chain of formations, associated with the
highlands bordering the S.W. and the W. flanks of the Mare Crisium. It
has a central mountain and other minor elevations on the floor. There is
a little ring between Alhazen and Hansen, never very conspicuous in the
telescope, which is plainly traceable in good photographs.
EIMMART.--A conspicuous ring-plain with bright walls on the N.W. margin
of the Mare Crisium. The E. border attains a height of 10,000 feet above
the interior, which, according to Schmidt, has a small central mountain.
There is a rill-like valley on the E. of the formation.
ORIANI.--An irregular object, 32 miles in diameter, somewhat difficult to
identify, N.W. of the last. There is a conspicuous crater on the N. of
it, with which it is connected by a prominent ridge.
PLUTARCH.--A fine ring-plain W. of Oriani, with regular walls, and,
according to Neison, with two central mountains, only one of which I have
seen. Both this formation and the last are beautifully shown in a
photograph taken August 19, 1891, at the Lick Observatory, when the
moon's age was 15 d. 10 hrs.
SENECA.--Rather smaller than Plutarch. Too near the limb for satisfactory
observation. Schmidt shows two considerable mountains in the interior.
The position of this object in Schmidt's chart is not accordant with its
place in Beer and Madler's map, nor in that of Neison.
HAHN.--A ring-plain, 46 miles in diameter, with a fine central mountain
and lofty peaks on the border, which is not continuous on the S. There is
a large and prominent crater on the E.
BEROSUS.--A somewhat smaller object of a similar type, N. of Hahn, but
with a loftier wall. There is a want of continuity also in the border,
the eastern and western sections of which, instead of joining, extend for
some distance towards the S., forming a narrow gorge or valley. Outside
the S.E. wall there is a small crater, and some irregular depressions on
the E. The minute central mountain is only seen with difficulty under a
low evening sun. The bright region between Hahn and Berosus and the
western flank of Cleomedes is an extensive plain, devoid of prominent
detail, and which, according to Neison, includes an area of 40,000 square
miles.
GAUSS.--A large, and nearly circular walled-plain, 111 miles in diameter,
situated close to the N.W. limb, and consequently always foreshortened
into a more or less elongated ellipse. But for this it would be one of
the grandest objects in the first quadrant. Under the designation of
"Mercurius Falsus" it received great attention from Schroter, who gives
several representations of it in his _Selenotopographische Fragmente_,
which, though drawn in his usual conventional style, convey a juster idea
of its salient features than many subsequent drawings made under far
better optical conditions. The border, especially on the W., is very
complex, and is discontinuous on the S., where it is intersected by more
than one pass, and is prolonged far beyond the apparent limits of the
formation. The most noteworthy feature is the magnificent mountain chain
which traverses the floor from N. to S. It is interesting to watch the
progress of sunset thereon, and see peak after peak disappear, till only
the great central boss and a few minute glittering points of light,
representing the loftier portions of the chain, remain to indicate its
position. Madler expatiates on the sublime view which would be obtained
by any one standing on the highest peak and observing the setting sun on
one side of him and the nearly "full" earth on the other; while beneath
him would lie a vast plain, shrouded in darkness, surrounded by the
brilliantly illuminated peaks on the lofty border, gradually passing out
of sunlight. In addition to the central mountain range, there are some
large rings, craters, hillocks, &c., on the floor; and on the inner slope
of the W. border there is a very large circular enclosure resembling a
ring-plain, not recorded in the maps. Schmidt shows a row of large
craters on the outer slope of the E. border. Of these, one is very
conspicuous under a low evening sun, by reason of its brilliant walls and
interior. In the region between Gauss and Berosus is a number of narrow
steep ridges which follow the curvature of the E. wall.
STRUVE.--A small irregularly-shaped formation, open towards the S.,
forming one of the curious group of unsymmetrical enclosures associated
with Messala. Its dark floor and a small dusky area on the N. indicate
its position under a high sun.
CARRINGTON.--A small ring-plain, belonging to the Messala group,
adjoining Schumacher on the N.W.
MERCURIUS.--This formation is 25 miles in diameter. A small crater stands
on the S.E. section of the wall. There is a longitudinal range in the
interior, and on the W. and N.W. the remains of two large walled-plains,
the more westerly of which is a noteworthy object under suitable
conditions. A short distance S. is a large, irregular, and very dark
marking. On the N., lies an immense bright plain, extending nearly to the
border of Endymion.
WEST LONGITUDE 60 deg. TO 40 deg.
TARUNTIUS.--Notwithstanding its comparatively low walls, this ring-plain,
44 miles in diameter, is a very conspicuous object under a rising sun.
Like Vitello and a few other formations, it has an inner ring on the
floor, concentric with the outer rampart, which I have often seen nearly
complete under evening illumination. There is a small bright crater on
the S.E. wall, and a larger one on the crest of the N.E. wall, with a
much more minute depression on the W. of it, the intervening space
exhibiting signs of disturbance. The upper portion of the wall is very
steep, contrasting in this respect with the very gentle inclination of
the _glacis_, which on the S. extends to a distance of at least 30 miles
before it sinks to the level of the surrounding country, the gradient
probably being as slight as 1 in 45. Two low dusky rings and a long
narrow valley with brilliant flanks are prominent objects on the plain E.
of Taruntius under a low evening sun.
SECCHI.--A partially enclosed little ring-plain S. of Taruntius, with a
prominent central mountain and bright walls. There is a short cleft
running in a N.E. direction from a point near the E. wall. Schmidt
represents it as a row of inosculating craters.
PICARD.--The largest of the craters on the surface of the Mare Crisium,
21 miles in diameter. The floor, which includes a central mountain, is
depressed about 2000 feet below the outer surface, and is surrounded by
walls rising some 3000 feet above the Mare. A small but lofty ring-plain,
Picard E, on the E., near the border of the Mare, is remarkable for its
change of aspect under different angles of illumination. A long curved
ridge running S. from this, with a lower ridge on the west, sometimes
resemble a large enclosure with a central mountain. Still farther S.,
there is another bright deep crater, _a_, with a large low ring adjoining
it on the S., abutting on the S.E. border of the Mare. Schroter bestowed
much attention on these and other formations on the Mare Crisium, and
attributed certain changes which he observed to a lunar atmosphere.
PEIRCE.--This formation, smaller than Picard, is also prominent, its
border being very bright. There is a central peak, which, though not an
easy object, I once glimpsed with a 4 inch Cook achromatic, and have seen
it two or three times since with an 8 1/2 inch Calver reflector. A small
crater, detected by Schmidt, which I once saw very distinctly under
evening illumination, stands on the floor at the foot of the W. wall.
Peirce A, a deeper formation, lies a little N. of Peirce, and has also,
according to Neison, a very slight central hill, which is only just
perceptible under the most favourable conditions. Schmidt appears to have
overlooked it.
PROCLUS.--One of the most brilliant objects on the moon's visible
surface, and hence extremely difficult to observe satisfactorily. It is
about 18 miles in diameter, with very steep walls, and, according to
Schmidt, has a small crater on its east border, where Madler shows a
break. It is questionable whether there is a central mountain. It is the
centre of a number of radiating light streaks which partly traverse the
Mare Crisium, and with those emanating from Picard, Peirce, and other
objects thereon, form a very complicated system.
MACROBIUS.--This, with a companion ring on the W., is a very beautiful
object under a low sun. It is 42 miles in diameter, and is encircled by a
bright, regular, but complex border, some 13,000 feet in height above the
floor. Its crest is broken on the E. by a large brilliant crater, and its
continuity is interrupted on the N. by a formation resembling a large
double crater, which is associated with a number of low rounded banks and
ridges extending some distance towards the N.W., and breaking the
continuity of the _glacis_. The W. wall is much terraced, and on the N.W.
includes a row of prominent depressions, well seen when the interior is
about half illuminated under a rising sun. The central mountain is of the
compound type, but not at all prominent. The companion ring, Macrobius C,
is terraced internally on the W., and the continuity of its N. border
broken by two depressions. There is a rill-valley between its N.E. side
and Macrobius.
CLEOMEDES.--A large oblong enclosure, 78 miles in diameter, with massive
walls, varying in altitude from 8000 to 10,000 feet above the interior.
The most noteworthy features in connection with the circumvallation are
the prominent depressions on the W. wall. Under a rising sun, when about
one-fourth of the floor is in shadow, three of these can be easily
distinguished, each resembling in form the analemma figure. There are two
other curious depressions at the S.W. end of the formation. On the dark
steel-grey floor are two irregular dusky areas, and a narrow but bright
central mountain, on which, according to Schmidt, stand two little
craters. There are two ring-plains on the S.W. quarter, and a group of
three associated craters on the N. side, one of which (A) Schroter
believed came into existence after he commenced to observe the formation,
a supposition that has been shown by Birt and others to be very
improbable.
TRALLES.--A large irregular crater, one of the deepest on the visible
surface of the moon, situated on the N.E. wall of Cleomedes. There is a
crater on its N. wall, and, according to Schmidt, some ridges and three
closely associated craters on the floor.
BURCKHARDT.--This object, situated on an apparent extension of the W.
wall of Cleomedes, is 35 miles in diameter, with a lofty border, rising
on the E. to an altitude of nearly 13,000 feet. It has a prominent
central mountain and some low ridges on the floor, which, together with
two minute craters on the S.W. wall, I have seen under a low angle of
morning illumination. It is flanked both on the E. and W. by deep
irregular depressions, which present the appearance of having once been
complete formations.
GEMINUS.--A fine regular ring-plain, 54 miles in diameter, nearly
circular, with bright walls, rising on the E. to a height of more than
12,000 feet, and on the opposite side to nearly 16,000 feet above the
floor. Their crest is everywhere very steep, and the inner slope is much
terraced. There is a small but conspicuous mountain in the interior; N.
of which I have seen a long ridge, where Schmidt shows some hillocks. Two
fine clefts are easily visible within the ring, one running for some
distance on the S.E. side of the floor, mounting the inner slope of the
S.W. border to the summit ridge (where it is apparently interrupted), and
then striking across the plain in a S.W. direction. Here it is
accompanied for a short distance by a somewhat coarser companion, running
parallel to it on the N. The other cleft occupies a very similar position
on the N.W. side of the floor at the inner foot of the wall. On several
occasions, when observing this formation and the vicinity, I have been
struck by its peculiar colour under a low evening sun. At this time the
whole region appears to be of a warm light brown or sepia tone.
BERNOUILLI.--A very deep ring-plain on the W. side of Geminus. Under
evening illumination its lofty W. wall, which rises to a height of nearly
13,000 feet above the floor, is conspicuously brilliant. This formation
exhibits a marked departure from the circular type, being bounded by
rectilineal sides. The inner slope of the W. wall is slightly terraced.
The border on the S. is much lower than elsewhere, as is evident when the
formation is on the evening terminator. On the N. is the deep crater
Messala _a_.
NEWCOMB.--The most prominent of a group of formations standing in the
midst of the Haemus Mountains. Its crest is nearly 12,000 feet above the
floor, on which there are some hills.
MESSALA.--This fine walled-plain, nearly 70 miles in diameter, is, with
its surroundings, an especially interesting object when observed under a
low angle of illumination. Its complex border, though roughly circular,
displays many irregularities in outline, due mainly to rows of
depressions. The best view of it is obtained when the W. wall is on the
evening terminator. At this phase, if libration is favourable, the
manifold details of its very uneven and apparently convex floor are best
seen. On the S.W. side is a group of large craters associated with a
number of low hills, of which Schmidt shows five; but I have seen many
more, together with several ridges between them and the E. wall. I noted
also a cleft, or it may be a narrow valley, running from the foot of the
N.W. wall towards the centre. On the floor, abutting on the N.E. border,
is a semicircular ridge of considerable height, and beyond the border on
the N.E. there is another curved ridge, completing the circle, the wall
forming the diameter. This formation is clearly of more ancient date than
Messala, as the N.E. wall of the latter has cut through it. Where Messala
joins Schumacher there is a break in the border, occupied by three deep
depressions.
SCHUMACHER.--A large irregular ring-plain, 28 miles in diameter,
associated with the N. wall of Messala, and having other smaller rings
adjoining it on the E. and N. The interior seems to be devoid of detail.
HOOKE.--Another irregular ring-plain, 28 miles in diameter, on the N.E.
of Messala. There is a bright crater of considerable size on the S.W.,
which is said to be more than 6000 feet in depth, and, according to
Neison, is visible as a white spot at full. There is a smaller crater on
the slope of the N.W. wall.
SHUCKBURGH.--A square-shaped enclosure on the N. of the last, with a
comparatively low border. It has a conspicuous crater at its N.W. corner.
BERZELIUS.--A considerable ring-plain of regular form, with low walls and
dark interior, on which there is a central peak, difficult to detect.
FRANKLIN.--A ring-plain, 33 miles in diameter, which displays a
considerable departure from the circular type, as the border is in great
part made up of rectilineal sections. Both the W. and N.E. wall is much
terraced, and rises about 8000 feet above the dark floor, on the S. part
of which there is a long ridge. There is a bright little isolated
mountain on the plain E. of the formation, and a conspicuous craterlet on
the N.W. An incomplete ring, with a very attenuated border, abuts on the
S. side of Franklin.
CEPHEUS.--A peculiarly shaped ring-plain, 27 miles in diameter. The E.
border is nearly rectilineal, while on the W., the wall forms a bold
curve. There is a very brilliant crater on the summit of this section,
and a central mountain on the floor. The W. wall is much terraced. W. of
Cepheus, close to the brilliant crater, there is a cleft or narrow valley
running N. towards Oersted.
OERSTED.--An oblong formation with very low walls, scarcely traceable on
the S.E., except when near the terminator. There is a conspicuous crater
on the N.W. side of the floor, and a curious square enclosure, with a
crater on its W. border, abutting on the N.E. wall.
CHEVALLIER.--An inconspicuous object enclosed by slightly curved ridges.
It includes a deep bright crater. On the N. is a low square formation and
a long ridge running N. from it. Just beyond the N.E. wall is the fine
large crater, Atlas A, with a much smaller but equally conspicuous crater
beyond. A has a central hill, which, in spite of the bright interior, is
not a difficult feature.
ATLAS.--This, and its companion Hercules on the E., form under oblique
illumination a very beautiful pair, scarcely surpassed by any other
similar objects on the first quadrant. Its lofty rampart, 55 miles in
diameter, is surmounted by peaks, which on the N. tower to an altitude of
nearly 11,000 feet. It exhibits an approach to a polygonal outline, the
lineal character of the border being especially well marked on the N. The
detail on the somewhat dark interior will repay careful scrutiny with
high powers. There is a small but distinct central mountain, south of
which stands a number of smaller hills, forming with the first a circular
arrangement, suggestive of the idea that they represent the relics of a
large central crater. Several clefts may be seen on the floor under
suitable illumination, among them a forked cleft on the N.E. quarter, and
two others, originating at a dusky pit of irregular form situated near
the foot of the S.E. wall, one of which runs W. of the central hills, and
the other on the opposite side. A ridge, at times resembling a light
marking, extends from the central mountain to the N. border. During the
years 1870 and 1871 I bestowed some attention on the dusky pit, and was
led to suspect that both it and the surrounding area vary considerably in
tone from time to time. Professor W.H. Pickering, observing the formation
in 1891 with a 13 inch telescope under the favourable atmospheric
conditions which prevail at Arequipa, Peru, confirmed this supposition,
and has discovered some very interesting and suggestive facts relating to
these variations, which, it is hoped, will soon be made public. On the
plain a short distance beyond the foot of the _glacis_ of the S.E. wall,
I have frequently noted a second dusky spot, from which proceeds, towards
the E., a long rill-like marking. On the N. there is a large formation
enclosed by rectilineal ridges. The outer slopes of the rampart of Atlas
are very noteworthy under a low sun.
HERCULES.--The eastern companion of Atlas, a fine ring-plain, about 46
miles in diameter, with a complex border, rising some 11,000 feet above a
depressed floor. There are few formations of its class and size which
display so much detail in the shape of terraces, apparent landslips, and
variation in brightness. In the interior, S.E. of the centre, is a very
conspicuous crater, which is visible as a bright spot when the formation
itself is hardly traceable, two large craterlets slightly N. of the
centre, and several faint little spots on the east of them. The latter,
detected some years ago by Herr Hackel of Stuttgart, are arranged in the
form of a horse-shoe. There are two small contiguous craters on the S.E.
wall, one of which, a difficult object, was recently detected by Mr. W.H.
Maw, F.R.A.S. The well-known wedge-shaped protuberance on the S. wall is
due to a large irregular depression. On the bright inner slope of the N.
wall are manifest indications of a landslip.
ENDYMION.--A large walled-plain, 78 miles in diameter, enclosed by a
lofty, broad, bright border, surmounted in places by peaks which attain a
height of more than 10,000 feet above the interior, one on the W.
measuring more than 15,000 feet. The walls are much terraced and exhibit
two or three breaks. The dark floor appears to be devoid of detail.
Schmidt, however, draws two large irregular mounds E. of the centre, and
shows four narrow light streaks crossing the interior nearly parallel to
the longer axis of the formation.
DE LA RUE.--Notwithstanding its great extent, this formation hardly
deserves a distinctive name, as from the lowness of its border it is
scarcely traceable in its entirety except under very oblique light.
Schmidt, nevertheless, draws it with very definite walls, and shows
several ridges and small rings in the interior. Among these objects, a
little E. of the centre, there is a prominent peak.
STRABO.--A small walled-plain, 32 miles in diameter, connected with the
N. border of the last.
THALES.--A bright formation, also associated with the N. side of De la
Rue, adjoining Strabo on the N.E. Schmidt shows a minute hill in the
interior.
There are several unnamed formations, large and small, between De la Rue
and the limb, some of which are well worthy of examination.
WEST LONGITUDE 40 deg. TO 20 deg.
MASKELYNE.--A regular ring-plain, 19 miles in diameter, standing almost
isolated in the Mare Tranquilitatis. The floor, which includes a central
mountain, is depressed some 3000 feet below the surrounding surface.
There are prominent terraces on the inner slope of the walls. Schmidt
shows no craters upon them, but Madler draws a small one on the E., the
existence of which I can confirm.
MANNERS.--A brilliant little ring-plain, 11 miles in diameter, on the
S.E. side of the Mare Tranquilitatis. There appears to be no detail
whatever in connection with its wall. It has a distinct central mountain.
About three diameters distant on the S.W. there is a bright crater,
omitted by Madler and Neison.
ARAGO.--A much larger formation, 18 miles in diameter, N. of the last,
with a small crater on its N. border, and exhibiting two or three spurs
from the wall on the opposite side. The inner slopes are terraced, and
there is a small central mountain. There are two curious circular
protuberances on the Mare E. of Arago, which are well seen when the W.
longitude of the morning terminator is about 19 deg., and a long cleft,
passing about midway between them, and extending from the foot of the E.
wall to a small crater on the edge of the Mare near Sosigenes. Another
cleft, also terminating at this crater, runs towards Arago and the more
northerly of the protuberances.
CAUCHY.--A bright little crater, not more than 7 or 8 miles in diameter,
on the W. side of the Mare Tranquilitatis, N.E. of Taruntius. It has a
peak on its W. rim considerably loftier than the rest of the wall, which
is visible as a brilliant spot at sunrise long before the rest of the
rampart is illuminated. On the S. there are two bright longitudinal
ridges ranging from N.E. to S.W. These stand in the position where Neison
draws two straight clefts. The Cauchy cleft, however, lies N. of these,
and terminates, as shown by Schmidt, among the mountains N.E. of
Taruntius. I have seen it thus on many occasions, and it is so
represented in a drawing by M.E. Stuvaert (_Dessins de la Lune_). There
is a number of minute craters and mounds standing on the S. side of this
cleft, and many others in the vicinity.
JANSEN.--Owing to its comparatively low border, this is not a very
conspicuous object. It is chiefly remarkable for the curious arrangement
of the mountains and ridges on the S. and W. of it. There is a bright
little crater on the S. side of the floor, and many noteworthy objects of
the same class in the neighbourhood. The mountain arm running S., and
ultimately bending E., forms a large incomplete hook-shaped formation
terminating at a ring-plain, Jansen B. The ridges in the Mare
Tranquilitatis between Jansen B. and the region E. of Maskelyne display
under a low sun foldings and wrinklings of a very extraordinary kind.
MACLEAR.--A conspicuous ring-plain about 16 miles in diameter. The dark
floor includes, according to Madler, a delicate central hill which
Schmidt does not show. Neison, however, saw a faint greyish mark, and an
undoubted peak has been subsequently recorded. I have not succeeded in
seeing any detail within the border, which in shape resembles a triangle
with curved sides.
ROSS.--A somewhat larger ring-plain of irregular form, on the N.W. of the
last. There are gaps on the bright S.W. border and a crater on the S.E.
wall. The central mountain is an easy feature.
PLINIUS.--This magnificent object reminds one at sunrise of a great
fortress or redoubt erected to command the passage between the Mare
Tranquilitatis and the Mare Serenitatis. It is 32 miles in diameter, and
is encompassed by a very massive rampart, rising at one peak on the E. to
more than 6000 feet above the interior, and displaying, especially on the
S.E., and N., many spurs and buttresses. The exterior slopes at sunrise,
and even when the sun is more than 10 deg. above the horizon, are seen to
be traversed by wide and deep valleys. The S. _glacis_ is especially
broad, extending to a distance of 10 or 12 miles before it runs down to
the level of the plain. The shape of the circumvallation, when it is
fully illuminated, approximates very closely to that of an equilateral
triangle with curved sides. There are two bright little craters on the
outer slope, just below the summit ridge on the S.E., and another,
larger, on the N. wall, in which it makes a prominent gap. The interior
is considerably brighter than the surface of the surrounding Mare, and, a
little S. of the centre, includes two crater-like objects with broken
rims. These assume different aspects under different conditions of
illumination, and it is only when the floor is lighted by a comparatively
low morning sun, that their true character is apparent. On the N.W.
quarter of the interior are two smaller distinct craters, and a square
arrangement of ridges. On the N.E. there are some hillocks and minor
elevations. The Plinius rills form an especially interesting system, and
under favourable conditions may be seen in their entirety with a good 4
inch refractor, about the time when the morning terminator passes through
Julius Caesar. They consist of three long fissures, originating amid the
Haemus highlands, on the S. side of the Mare Serenitatis, and diverging
towards the W. The most southerly commences S.S.E. of the Acherusian
promontory (a great headland, 5000 feet high, at the W. termination of
the Haemus range), and, following a somewhat undulating course, runs up
to the N. side of Dawes. Under a low evening sun, I have remarked many
inequalities in the width of that portion of it immediately N. of
Plinius, which appear to indicate that it is here made up of rows of
inosculating craters. The cleft north of this originates very near it,
passes a little S. of the promontory, and runs to the E. edge of the
plateau surrounding Dawes. The third and most northerly cleft begins at a
point immediately N. of the promontory, cuts through the S. end of the
well-known Serpentine ridge on the Mare Serenitatis, and, after following
a course slightly concave to the N., dies out on the N. side of the
plateau. This cleft forms the line of demarcation between the dark tone
of the Mare Serenitatis and the light hue of the Mare Tranquilitatis,
traceable under nearly every condition of illumination, and prominent in
all good photographs.
DAWES.--A ring-plain 14 miles in diameter, situated N.W. of Plinius, on a
nearly circular light area. Its bright border rises to a height of 2000
feet above the Mare, and includes a central mountain, a white marking on
the E., and a ridge running from the mountain to the S. wall. There are
two closely parallel clefts on the N. side of the plateau running from E.
to W., that nearer Dawes being the longer, and having a craterlet
standing upon it about midway between its extremities. At its W.
termination there is a crater-row running at right angles to it. The
light area appears to be bounded on the E. by a low curved bank.
VITRUVIUS.--A ring-plain 19 miles in diameter with bright but not very
lofty walls, situated among the mountains near the S.W. side of the Mare
Serenitatis. It is surrounded by a region remarkable for its great
variability in brightness. There is a large bright ring-plain on the W.,
with a less conspicuous companion on the S. of it.
MARALDI.--A deep but rather inconspicuous formation, bounded on the W. by
a polygonal border. A small ring-plain with a central mountain is
connected with the S.W. wall; and, running in a N. direction from this,
is a short mountain arm which joins a large circular enclosure with a low
broken border standing on the N. side of the Mare Tranquilitatis.
LITTROW.--A peculiar ring-plain, rather smaller than the last, some
distance N. of Vitruvius, on the rocky W. border of the Mare Serenitatis.
It is shaped like the letter D, the straight side facing the W. There is
a distinct crater on the N. wall. On the N.W. it is flanked by three
irregular ring-plains, and on the S.E. by a fourth. Neison shows two
small mountains on the floor, but Schmidt, whose drawing is very true to
nature, has no detail whatever. A fine cleft may be traced from near the
foot of the E. wall to Mount Argaeus, passing S. of a bright crater on
the Mare E. of Littrow. It extends towards the Plinius system, and is
probably connected with it.
MOUNT ARGAEUS.--There are few objects on the moon's visible surface which
afford a more striking and beautiful picture than this mountain and its
surrounding heights with their shadows a few hours after sunrise. It
attains an altitude of more than 8000 feet above the Mare, and at a
certain phase resembles a bright spear-head or dagger. There is a well-
defined rimmed depression abutting on its southern point.
ROMER.--A prominent formation of irregular outline, 24 miles in diameter,
situated in the midst of the Taurus highlands. It has a very large
central mountain, a crater on the N. side of the floor, and terraced
inner slopes. Some distance on the N. is another ring, nearly as large,
with a crater on its S. rim, and between this and Posidonius is another
with a wide gap on the S. and a crater on its N. border. One of the most
remarkable crater-rills on the moon runs from the E. side of Romer
through this latter ring, and then northwards on to the plain W. of
Posidonius. Under suitable conditions, it can be seen as such in a 4 inch
achromatic. It is easily traceable as a rill in a photograph of the N.
polar region of the moon taken by MM. Henry at the Paris Observatory, and
recently published in _Knowledge_.
LE MONNIER.--A great inflection or bay on the W. border of the Mare
Serenitatis S. of Posidonius. Like many other similar formations on the
edges of the Maria, it appears at one time or other to have had a
continuous rampart, which on the side facing the "sea" has been
destroyed. In this, as in most of the other cases, relics of the ruin are
traceable under oblique light. A fine crescent-shaped mountain, 3000 feet
high, stands near the S. side of the gap, and probably represents a
portion of a once lofty wall. It will repay the observer to watch the
progress of sunrise on the whole of the W. coast-line of the Mare up to
Mount Argaeus.
POSIDONIUS.--This magnificent ring-plain is justly regarded as one of the
finest telescopic objects in the first quadrant. Its narrow bright wall
with its serrated shadow, the conspicuous crater, the clefts and ridges
and other details on the floor, together with the beautiful group of
objects on the neighbouring plain, and the great Serpentine ridge on the
E., never fail to excite the interest of the observer. The
circumvallation, which is far from being perfectly regular, is about 62
miles in diameter, and, considering its size, is not remarkable for its
altitude, as it nowhere exceeds 6000 feet above the interior, which is
depressed about 2000 feet below the surrounding plain. Its continuity,
especially on the E., is interrupted by gaps. On the N., the wall is
notably deformed. It is broader and more regular on the W., where it
includes a large longitudinal depression, and on the N.W. section stand
two bright little ring-plains. On the floor, which shines with a
glittering lustre, are the well-marked remains of a second ring, nearly
concentric with the principal rampart, and separated from it by an
interval of nine or ten miles. The most prominent object, however, is the
bright crater a little E. of the centre. This is partially surrounded on
the W. by three or four small bright mountains, through which runs in a
meridional direction a rill-valley, not easily traced as a whole, except
under a low sun. There is another cleft on the N.E. side of the interior,
which is an apparent extension of part of the inner ring, a transverse
rill-valley on the N., a fourth _quasi_ rill on the N.W., and a fifth
short cleft on the S. part of the floor. Between the principal crater and
the S.E. wall are two smaller craters, which are easy objects. Beyond the
border on the N., in addition to Daniell, are four conspicuous craters
and many ridges.
CHACORNAC.--This object, connected with Posidonius on the S.W., is
remarkable for the brilliancy of its border and the peculiarity of its
shape, which is very clearly that of an irregular pentagon with linear
sides. I always find the detail within very difficult to make out. Two or
more low ridges, traversing the floor from N. to S., and a small crater,
are, however, clearly visible under oblique illumination. Schmidt draws a
crater-rill, and Neison two parallel rills on the floor,--the former
extends in a southerly direction to the W. side of Le Monnier.
DANIELL.--A bright little ring-plain N. of Posidonius. It is connected
with a smaller ring-plain on the N.W. wall of the latter by a low ridge.
BOND, G.P.--A small bright ring-plain 12 miles in diameter, W. of
Posidonius. Neison shows a crater both on the N. and S. rim. Schmidt
omits these.
MAURY.--A bright deep little ring-plain, about 12 miles in diameter, on
the W. border of the Lacus Somniorum. It is the centre of four prominent
hill ranges.
GROVE.--A bright deep ring-plain, 15 miles in diameter, in the Lacus
Somniorum, with a border rising 7000 feet above a greatly depressed
floor, which includes a prominent mountain.
MASON.--The more westerly of two remarkable ring-plains, situated in the
highlands on the S. side of the Lacus Mortis. It is 14 miles in diameter,
has a distinct crater on its S. wall, and, according to Schmidt, a crater
on the E. side of the floor.
PLANA.--A formation 23 miles in diameter, closely associated with the
last. Neison states that the floor is convex and higher than the
surrounding region. It has a triangular-shaped central mountain, a
crater, and at least three other depressions on the S.W. wall where it
joins Mason.
BURG.--A noteworthy formation, 28 miles in diameter, on the Mare, N. of
Plana. The floor is concave, and includes a very large bright mountain,
which occupies a great portion of it. The interior slopes are prominently
terraced, and there are several spurs associated with the _glacis_ on the
S. and N.E. A distinct cleft runs from the N. side of the formation to
the S.E. border of the Lacus Somniorum, which is crossed by another
winding cleft running from a crater E. of Plana towards the N.E.
BAILY.--A small ring-plain, N. of Burg, flanked by mountains, with a
large bright crater on the W. The group of mountains standing about
midway between it and Burg are very noteworthy.
GARTNER.--A very large walled-plain with a low incomplete border on the
E., but defined on the W. by a lofty wall. Schmidt shows a curved crater-
row on the W. side of the floor.
DEMOCRITUS.--A deep regular ring-plain, about 25 miles in diameter, with
a bright central mountain and lofty terraced walls.
ARNOLD.--A great enclosure, bounded, like so many other formations
hereabouts, by straight parallel walls. There is a somewhat smaller
walled-plain adjoining it on the W.
MOIGNO.--A ring-plain with a dark floor, adjoining the last on the N.E.
There is a conspicuous little crater in the interior.
EUCTEMON.--This object is so close to the limb that very little can be
made of its details under the most favourable conditions. According to
Neison, there is a peak on the N. wall 11,000 feet in height.
METON.--A peculiarly-shaped walled-plain of great size, exhibiting
considerable parallelism. The floor is seen to be very rugged under
oblique illumination.
WEST LONGITUDE 20 deg. TO 0 deg.
SABINE.--The more westerly of a remarkable pair of ring-plains, of which
Ritter is the other member, situated on the E. side of the Mare
Tranquilitatis a little N. of the lunar equator. It is about 18 miles in
diameter, and has a low continuous border, which includes a central
mountain on a bright floor. From a mountain arm extending from the S.
wall, run in a westerly direction two nearly parallel clefts skirting the
edge of the Mare. The more southerly of these terminates near a
depression on a rocky headland projecting from the coast-line, and the
other stops a few miles short of this. A third cleft, commencing at a
point N.E. of the headland, runs in the same direction up to a small
crater near the N. end of another cape-like projection. At 8 h. on April
9, 1886, when the morning terminator bisected Sabine, I traced it still
farther in the same direction. All these clefts exhibit considerable
variations in width, but become narrower as they proceed westwards.
RITTER.--Is very similar in every respect to the last. A curved rill
mentioned by Neison is on the N.E. side of the floor and is concentric
with the wall. On the N. side of this ring-plain are three conspicuous
craters, the two nearer being equal in size and the third much smaller.
SCHMIDT.--A bright crater at the foot of the S. slope of Ritter.
DIONYSIUS.--This crater, 13 miles in diameter, is one of the brightest
spots on the lunar surface. It stands on the E. border of the Mare, about
30 miles E.N.E. of Ritter. A distinct crater-row runs round its outer
border on the W., and ultimately, as a delicate cleft, strikes across the
Mare to the E. side of Ritter. Both crater-row and cleft are easy objects
in a 4 inch achromatic under morning illumination.
ARIADAEUS.--A bright little crater of polygonal shape, with another
crater of about one-third the area adjoining it on the N.W., situated on
the rocky E. margin of the Mare Tranquilitatis, N.E. of Ritter. A short
cleft runs from it towards the latter, but dies out about midway. A
second cleft begins near its termination, and runs up to the N.E. wall of
Ritter. E. of this pair a third distinct cleft, originating at a point on
the coast-line about midway between Ariadaeus and Dionysius, ends near
the same place on the border. There is a fourth cleft extending from the
N. side of a little bay N. of Ariadaeus across the Mare to a point N.W.
of the more northerly of the three craters N. of Ritter. At a small
crater on the S. flank of the mountains bordering the little bay N. of
Ariadaeus originates one of the longest and most noteworthy clefts on the
moon's visible surface, discovered more than a century ago by Schroter of
Lilienthal. It varies considerably in breadth and depth, but throughout
its course over the plain, between Ariadaeus and Silberschlag, it can be
followed without difficulty in a very small telescope. E. of the latter
formation, towards Hyginus (with which rill-system it is connected), it
is generally more difficult. A few miles E. of Ariadaeus it sends out a
short branch, running in a S.W. direction, which can be traced as a fine
white line under a moderately high sun. It is interesting to follow the
course of the principal cleft across the plain, and to note its progress
through the ridges and mountain groups it encounters. In the great Lick
telescope it is seen to traverse some old crater-rings which have not
been revealed in smaller instruments. About midway between Ariadaeus and
Silberschlag it exhibits a duplication for a short distance, first
detected by Webb.
DE MORGAN.--A brilliant little crater, 4 miles in diameter, on the plain
S. of the Ariadaeus cleft.
CAYLEY.--A very deep bright crater, with a dark interior, N. of the last,
and more than double its diameter. There is a second crater between this
and the cleft.
WHEWELL.--Another bright little ring, about 3 miles in diameter, some
distance to the E. of De Morgan and Cayley.
SOSIGENES.--A small circular ring-plain, 14 miles in diameter, with
narrow walls, a central mountain, and a minute crater outside the wall on
the E.; situated on the E. side of the Mare Tranquilitatis, W. of Julius
Caesar. There is another crater, about half its diameter, on the S.,
connected with it by a low mound. This has a still smaller crater on the
W. of it.
JULIUS CAESAR.--A large incomplete formation of irregular shape. The wall
on the E. is much terraced, and forms a flat "S" curve. The summit ridge
is especially bright, and has a conspicuous little crater upon it. On
the W. is a number of narrow longitudinal valleys trending from N. to S.,
included by a wide valley which constitutes the boundary on this side.
The border on the S. consists of a number of low rounded banks, those
immediately E. of Sosigenes being traversed by several shallow valleys,
which look as if they had been shaped by alluvial action. There is a
brilliant little hill at the end of one of these valleys, a few miles E.
of Sosigenes. The floor of Julius Caesar is uneven in tone, becoming
gradually duskier from S. to N., the northern end ranking among the
darkest areas on the lunar surface. There are at least three large
circular swellings in the interior. A long low mound, with two or three
depressions upon it, bounds the wide valley on the E. side.
GODIN.--A square-shaped ring-plain, 28 miles in diameter, with rounded
corners. The bright rampart is everywhere lofty, except on the S., is
much terraced, and includes a central mountain. On the S. a curious
trumpet-shaped valley, extending some distance towards the S.W., and
bounded by bright walls, is a noteworthy feature at sunrise. There are
other longitudinal valleys with associated ridges on this side of the
formation, all running in the same direction. There is a large bright
crater outside the border on the N.E., and, between it and the wall,
another, smaller, which is readily seen under a high sun.
AGRIPPA.--A ring-plain 28 miles in diameter on the N. of the last, with a
terraced border rising to a height of between 7000 and 8000 feet above
the floor, which contains a large bright central mountain and two craters
on the S. The shape of this formation deviates very considerably from
circularity, the N. wall, on which stands a small crater, being almost
lineal. On the W., at a distance of a few miles, runs the prominent
mountain range, extending northwards nearly up to the E. flank of Julius
Caesar, which bounds the E. side of the great Ariadaeus plain. Between
this rocky barrier and Agrippa is a very noteworthy enclosure containing
much minute detail and a long straight ridge resembling a cleft. A few
miles N. of Agrippa stands a small crater; at a point W. of which the
Hyginus cleft originates.
SILBERSCHLAG.--A very brilliant crater, 8 or 9 miles in diameter,
connected with the great mountain range just referred to. The Ariadaeus
cleft cuts through the range a few miles N. of it. This neighbourhood at
sunrise presents a grand spectacle. With high powers under good
atmospheric conditions, the plain E. of the mountains is seen to be
traversed by a number of shallow winding valleys, trending towards
Agrippa, and separated by low rounded hills which have all the appearance
of having been moulded by the action of water.
BOSCOVICH.--This is not a very striking telescopic object under any
phase, on account of its broken, irregular, and generally ill-defined
border. It is, however, remarkable as being one of the darkest spots on
the visible surface: in this respect a fit companion to Julius Caesar,
its neighbour on the W. Schmidt shows some ridges within it.
RHAETICUS.--A very interesting formation, about 25 miles in diameter,
situated near the lunar equator, with a border intersected by many
passes. A deep rill-like valley winds round its eastern _glacis_,
commencing on the S. at a small circular enclosure standing at the end of
a spur from the wall; and, after crossing a ridge W. of a bright little
crater on the N. of the formation, apparently joins the most easterly
cleft of the Triesnecker system. A cleft traverses the N. side of the
floor of Rhaeticus, and extends across the plain on the E. as far as the
N. side of Reaumur.
TRIESNECKER.--Apart from being the centre of one of the most remarkable
rill-systems on the moon, this ring-plain, though only about 14 miles in
diameter, is an object especially worthy of examination under every
phase. At sunrise, and for some time afterwards, owing to the superior
altitude of the N.W. section of the wall, a considerable portion of the
border on the N. and N.E. is masked by its shadow, which thus appears to
destroy its continuity. On more than one occasion, friends, to whom I
have shown this object under these conditions, have likened it to a
breached volcanic cone, a comparison which at a later stage is seen to be
very inappropriate. The rampart is terraced within, and exhibits many
spurs and buttresses without, especially on the N.W. The central mountain
is small and not conspicuous. The rill-system is far too complicated to
be intelligibly described in words. It lies on the W. side of the
meridian passing through the formation, and extends from the N. side of
Rhaeticus to the mountain-land lying between Ukert and Hyginus on the N.
Birt likened these rills to "an inverted river system," a comparison
which will commend itself to most observers who have seen them on a good
night, for in many instances they appear to become wider and deeper as
they approach higher ground. Published maps are all more or less
defective in their representations of them, especially as regards that
portion of the system lying N. of Triesnecker.
HYGINUS.--A deep depression, rather less than 4 miles across, with a low
rim of varying altitude, having a crater on its N. edge. This formation
is remarkable for the great cleft which traverses it, discovered by
Schroter in 1788. The coarser parts of this object are easily visible in
small telescopes, and may be glimpsed under suitable conditions with a 2
inch achromatic. Commencing a little W. of a small crater N. of Agrippa,
it crosses, as a very delicate object, a plain abounding in low ridges
and shallow valleys, and runs nearly parallel to the eastern extension of
the Ariadaeus rill. As it approaches Hyginus it becomes gradually
coarser, and exhibits many expansions and contractions, the former in
many cases evidently representing craters. When the phase is favourable,
it can be followed across the floor of Hyginus, and I have frequently
seen the banks with which it appears to be bounded (at any rate within
the formation), standing out as fine bright parallel lines amid the
shadow. On reaching the E. wall, it turns somewhat more to the N.,
becomes still coarser and more irregular in breadth, and ultimately
expands into a wide valley on the N.E. It is connected with the Ariadaeus
cleft by a branch which leaves the latter at an acute angle on the plain
E. of Silberschlag, and joins it about midway between its origin N. of
Agrippa and Hyginus. It is also probably joined to the Triesnecker system
by one or more branches E. of Hyginus.
On May 27, 1877, Dr. Hermann Klein of Cologne discovered, with a 5 1/2
inch Plosel dialyte telescope, a dark apparent depression without a rim
in the Mare Vaporum, a few miles N.W. of Hyginus, which, from twelve
years' acquaintance with the region, he was certain had not been visible
during that period. On the announcement of this discovery in the
_Wochenschrift fur Astronomie_ in March of the following year, the
existence of the object described by Dr. Klein was confirmed, and it was
sedulously scrutinised under various solar altitudes. To most observers
it appeared as an ill-defined object with a somewhat nebulous border,
standing on an irregularly-shaped dusky area, with two or more small dark
craters and many low ridges in its vicinity. A little E. of it stands a
curious spiral mountain called the Schneckenberg. The question as to
whether Hyginus N. (as the dusky spot is called) is a new object or not,
cannot be definitely determined, as, in spite of a strong case in favour
of it being so, there remains a residuum of doubt and uncertainty that
can never be entirely cleared away. After weighing, however, all that can
be said "for and against," the hypothesis of change seems to be the most
probable.
UKERT.--This bright crater, 14 miles in diameter, situated in the region
N.E. of Triesnecker, is surrounded by a very complicated arrangement of
mountains; and on the N. and W. is flanked by other enclosures. It has a
distinct central mountain. Its most noteworthy feature is the great
valley, more than 80 miles long, which extends from N.E. to S.W. on the
E. side of it. This gorge is at least six miles in breadth, of great
depth, and is only comparable in magnitude with the well-known valley
which cuts through the Alps, W. of Plato. A delicate cleft, not very
clearly traceable as a whole, begins near its N. end, and terminates amid
the ramifications of the Apennines S. of Marco Polo.
TAQUET.--A conspicuous little crater on the S. border of the Mare
Serenitatis at the foot of the Haemus Mountains. A branch of the great
Serpentine ridge, which traverses the W. side of this plain and other
lesser elevations, runs towards it.
MENELAUS.--A conspicuously bright regular ring-plain, about 20 miles in
diameter, situated on the S. coast-line of the Mare Serenitatis, and
closely associated with the Haemus range. It has a brilliant central
mountain, but no visible detail on the walls. On the edge of the Mare,
S.W. of it, there is a curious square formation. The bright streak
traversing the Mare from N. to S., which is so prominently displayed in
old maps of the moon, passes through this formation.
SULPICIUS GALLUS.--Another brilliant object on the south edge of the Mare
Serenitatis, some distance E. of the last. It is a deep circular crater
about 8 miles in diameter, rising to a considerable height above the
surface. Its shadow under a low morning sun is prominently jagged. On the
E. are two bright mounds, and S. of that which is nearer the border of
the Mare, commences a cleft which, following the curvature of the coast-
line, terminates at a point in W. long. 9 deg. This object varies
considerably in width and depth. Another shorter and coarser cleft runs
S. of this across an irregularly shaped bay or inflexion in the border of
the Mare.
MANILIUS.--This, one of the most brilliant objects in the first quadrant,
is about 25 miles in diameter, with walls nearly 8000 feet above the
floor, which includes a bright central mountain. The inner slope of the
border on the E. is much terraced and contains some depressions. There is
a small isolated bright mountain 2000 feet high on the Mare Vaporum, some
distance to the E.
BESSEL.--A bright circular crater, 14 miles in diameter, on the S. half
of the Mare Serenitatis, and the largest object of its class thereon. Its
floor is depressed some 2000 feet below the surrounding surface, while
the walls, rising nearly 1600 feet above the plain, have peaks both on
the N. and S. about 200 feet higher. The shadows of these features, noted
by Schroter in 1797, and by many subsequent observers, are very
noteworthy. I have seen the shadow of a third peak about midway between
the two. One may faintly imagine the magnificent prospect of the coast-
line of the Mare with the Haemus range, which would be obtained were it
possible to stand on the summit of one of these elevations. It is
doubtful whether Bessel has a central mountain. Neither Madler nor
Schmidt have seen one, though Webb noted a peak on two occasions. I fail
to see anything within the crater. The bright streak crossing the Mare
from N. to S. passes through Bessel.
LINNE.--A formation on the E. side of the Mare Serenitatis, described by
Lohrmann and Madler as a deep crater, but which in 1866 was found by
Schmidt to have lost all the appearance of one. The announcement of this
apparent change led to a critical examination of the object by most of
the leading observers, and to a controversy which, if it had no other
result, tended to awaken an interest in selenography that has been
maintained ever since. According to Madler, the crater was more than 6
miles in diameter in his time, and very conspicuous under a low sun, a
description to which it certainly did not answer in 1867 or at any
subsequent epoch. It is anything but an easy object to see well, as there
is a want of definiteness about it under the best conditions, though the
minute crater, the low ridges, and the nebulous whiteness described by
Schmidt and noted by Webb and others, are traceable at the proper phase.
As in the case of Hyginus N, there are still many sceptics as regards
actual change, despite the records of Lohrmann and Madler; but the
evidence in favour of it seems to preponderate.
CONON.--A bright little crater, 11 miles in diameter, situated among the
intricacies of the Apennines, S. of Mount Bradley. It has a central hill,
which is not a difficult object.
ARATUS.--One of the most brilliant objects on the visible surface of the
moon, a crater 7 miles in diameter, S. of Mount Hadley, surrounded by the
lofty mountain arms and towering heights of the Apennines. A peak close
by on the N. is more than 10,000 feet, and another farther removed
towards the N.W. is over 14,000 feet in altitude.
AUTOLYCUS.--A ring-plain 23 miles in diameter, deviating considerably
from circularity, W. of Archimedes, on the Mare Imbrium, or rather on
that part of it termed the Palus Putredinis. Its floor, which contains an
inconspicuous central mountain, is depressed some 4000 feet below the
surrounding country. With a power of 150 on a 4 5/8 achromatic, Dr.
Sheldon of Macclesfield has seen two shallow crateriform depressions in
the interior, one nearly central, and the other about midway between it
and the N. wall. The wall is terraced within, and has a crater just below
its crest on the W., which, when the opposite border is on the morning
terminator, is seen as a distinct notch. Autolycus is the centre of a
minor ray-system.
ARISTILLUS.--A larger and much more elaborate ring-plain, 34 miles in
diameter, N. of Autolycus. Its complex wall, with its terraces within,
and its buttresses, radiating spurs, and gullies without, forms a grand
telescopic object under a low sun on a good night. It rises on the east
11,000 feet above the Mare, and is about 2000 feet lower on the W., while
the interior is depressed some 3000 feet. Its massive central mountain,
surmounted by many peaks, occupies a considerable area on the floor, and
exhibits a digitated outline at the base. On the S. and W. a number of
deep valleys radiate from the foot of the border, some of them extending
nearly as far as Autolycus. Shallower but more numerous and regular
features of the same class radiate towards the N.E. from the foot of the
opposite wall. On the N.W. are several curved ridges, all trending
towards Theaetetus. On the S.E. the surface is trenched by a number of
crossed gullies, well seen when the E. wall is on the morning terminator.
Just beyond the N. _glacis_ is a large irregular dusky enclosure with a
central mound, and another smaller low ring adjoining it on the S.E. The
visibility of these objects is very ephemeral, as they disappear soon
after sunrise. Aristillus is also the centre of a bright ray system.
THEAETETUS.--A conspicuous ring-plain, about 16 miles in diameter, in the
Palus Nebularum, N.W. of Aristillus. It is remarkable for its great
depth, the floor sinking nearly 5000 feet below the surface. Its walls,
7000 feet high on the W., are devoid of detail. The _glacis_ on the S.W.
has a gentle slope, and extends for a great distance before it runs down
to the level of the plain. Not far from the foot of the wall on the N. is
a row of seven or eight bright little hills, near the eastern side of
which originates a distinct cleft that crosses the Palus in a N.W.
direction, and terminates among mountains between Cassini and Calippus. I
have seen this object easily with a 4 inch achromatic.
CALIPPUS.--A bright ring-plain 17 miles in diameter, situated in the
midst of the intricate Caucasus Mountain range. On the E. is a brilliant
peak rising more than 13,000 feet above the Palus Nebularum, and nearer
the border, on the N.E., is a second, more than 500 feet higher, with
many others nearly as lofty in the vicinity. Calippus has not apparently
a central peak or any other features on the floor.
CASSINI.--This remarkable ring-plain, about 36 miles in diameter, is very
similar in character to Posidonius. It has a very narrow wall, nowhere
more than 4000 feet in height, and falling on the E. to 1500 feet. Though
a prominent and beautiful object under a low sun, its attenuated border
and the tone of the floor, which scarcely differs from that of the
surrounding surface, render it difficult to trace under a high angle of
illumination, and perhaps accounts for the fact that it escaped the
notice of Hevel and Riccioli; though it is certainly strange that a
formation which is thrown into such strong relief at sunrise and sunset
should have been overlooked, while others hardly more prominent at these
times have been drawn and described. The outline of Cassini is clearly
polygonal, being made up of several rectilineal sections. The interior,
nearly at the same level as the outside country, includes a large bright
ring-plain, A, 9 miles in diameter and 2600 feet in depth, which has a
good-sized crater on the S. edge of a great bank which extends from the
S.W. side of this ring-plain to the wall. On the E. side of the floor,
close to the inner foot of the border, is a bright deep crater about two-
thirds of the diameter of A, and between it and the latter Brenner has
seen three small hills. The outer slope of Cassini includes much detail.
On the S.W. is a row of shallow depressions just below the crest of the
wall, and near the foot of the slope is a large circular shallow
depression associated with a valley which runs partly round it. The shape
of the _glacis_ on the W. is especially noteworthy, the S.W. and N.W.
sides meeting at a slightly acute angle at a point 10 or 12 miles W. of
the summit of the ring. On the outer E. slope is a curious elongated
depression, and on the N. slope two large dusky rings, well shown by
Schmidt, but omitted in other maps. Most of these details are well within
the scope of moderate apertures. Perhaps the most striking view of
Cassini and its surroundings is obtained when the morning terminator is
on the central meridian.
ALEXANDER.--A large irregularly shaped plain, at least 60 miles in
longest diameter, enclosed by the Caucasus Mountains. On the S.W. and
N.W. the border is lineal. It has a dark level floor on which there is a
great number of low hills.
EUDOXUS.--A bright deep ring-plain, about 40 miles in diameter, in the
hilly region between the Mare Serenitatis and the Mare Frigoris, with a
border much broken by passes, and deviating considerably from
circularity. Its massive walls, rising more than 11,000 feet above the
floor on the W., and about 10,000 feet on the opposite side, are
prominently terraced, and include crater-rows in the intervening valleys,
while their outer slopes present a complicated system of spurs and
buttresses. There is a bright crater on the N. _glacis_, and some
distance beyond the wall on the N.W. is a small ring-plain, and on the
S.E. another, with a conspicuous crater between it and the wall. Neison
draws attention to an area of about 1400 square miles on the N.E. which
is covered with a great multitude of low hills. E. of Eudoxus are two
short crossed clefts, and on the N. a long cleft of considerable delicacy
running from N.E. to S.W. It was in connection with this formation that
Trouvelot, on February 20, 1877, when the terminator passed through
Aristillus and Alphonsus, saw a very narrow thread of light crossing the
S. part of the interior and extending from border to border. He noted
also similar appearances elsewhere, and termed them _Murs enigmatiques_.
ARISTOTELES.--A magnificent ring-plain, 60 miles in diameter, with a
complex border, surmounted by peaks, rising to nearly 11,000 feet above
the floor, one of which on the W., pertaining to a terrace, stands out as
a brilliant spot in the midst of shadow when the interior is filled with
shadow. The formation presents its most striking aspect at sunrise, when
the shadow of the W. wall just covers the floor, and the brilliant inner
slope of the E. wall with the little crater on its crest is fully
illuminated. At this phase the details of the terraces are seen to the
best advantage. The arrangement of the parallel ridges and rows of hills
on the N.E. and S.W. is likewise better seen at this time than under an
evening sun. A bright and deep ring-plain, about 10 miles in diameter,
with a distinct central mountain, is connected with the W. wall.
EGEDE.--A lozenge-shaped formation, about 18 miles from corner to corner,
bounded by walls scarcely more than 400 feet in height. It is
consequently only traceable under very oblique illumination.
THE GREAT ALPINE VALLEY.--A great wedge-shaped depression, cutting
through the Alps W. of Plato, from W.N.W. to E.S.E. It is more than 80
miles in length, and varies in breadth from 6 miles on the S. to less
than 4 miles on the N., where it approaches the S. border of the Mare
Frigoris. For a greater part of its extent it is bounded on the S.W. side
by a precipitous linear cliff, which, under a low evening sun, is seen to
be fringed by a row of bright little hills. These are traceable up to one
of the great mountain masses of the Alps, forming the S.W. side of the
great oval-shaped expansion of the valley, whose shape has been
appropriately compared to that of a Florence oil-flask, and which Webb
terms "a grand amphitheatre." On the opposite or N.E. side, the boundary
of the valley is less regular, following a more or less undulating line
up to a point opposite, and a little N. of, the great mountain mass,
where it abuts on a shallow _quasi_ enclosure with lofty walls, which,
projecting westwards, considerably diminish the width of the valley.
South of this lies another curved mountain ring, which still farther
narrows it. This curtailment in width represents the neck of the flask,
and is apparently about 16 or 17 miles in length, and from 3 to 4 miles
in breadth, forming a gorge, bordered on the W. by nearly vertical
cliffs, towering thousands of feet above the bottom of the valley; and on
the E. by many peaked mountains of still greater altitude. At the
entrance to the "amphitheatre," the actual distance between the colossal
rocks which flank the defile is certainly not much more than 2 miles.
From this standpoint the view across the level interior of the elliptical
plain would be of extraordinary magnificence. Towards the S., but more
than 12 miles distant, the outlook of an observer would be limited by
some of the loftiest peaks of the Alps, whose flanks form the boundary of
the enclosure, through which, however, by at least three narrow passes he
might perchance get a glimpse of the Mare Imbrium beyond. The broadest of
these aligns with the axis of the valley. It is hardly more than a mile
wide at its commencement on the S. border of the "amphitheatre," but
expands rapidly into a trumpet-shaped gorge, flanked on either side by
the towering heights of the Alps as it opens out on to the Mare. The
bottom, both of the "amphitheatre" and of the long wedge-shaped valley,
appears to be perfectly level, and, as regards the central portion of the
latter, without visible detail. Under morning illumination I have,
however, frequently seen something resembling a ridge partially crossing
"the neck," and, near sunset, a tongue of rock jutting out from the E.
flank of the constriction, and extending nearly from side to side. At the
base of the cliff bordering the valley on the S.W., five or six little
circular pits have been noted, some of which appear to have rims. They
were seen very perfectly with powers of 350 and 400 on an 8 1/2 inch
Calver reflector at 8 h. on January 25, 1885, and have been observed, but
less perfectly, on subsequent occasions. The most northerly is about 10
miles from the N.W. end of the formation, and the rest occur at nearly
regular intervals between it and "the neck." In the neighbourhood of the
valley, on either side, there are several bright craters. Three stand
near the N.E. edge, and one of considerable size near the N.W. end on the
opposite side. A winding cleft crosses the valley about midway, which,
strange to say, is not shown in the maps, though it may be seen in a 4
inch achromatic. It originates apparently at a bright triangular mountain
on the plain S.W. of the valley, and, after crossing the latter somewhat
obliquely, is lost amid the mountains on the opposite side. That portion
of it on the bottom of the valley is easily traceable under a high light
as a white line. The region N. of the Alps on the S.W. side of the valley
presents many details worthy of examination. Among them, parallel rows of
little hills, all extending from N.W. to S.E. There is also a number of
still smaller objects of the same type on the E. side. The great Alpine
valley, though first described by Schroter, is said to have been
discovered on September 22, 1727, by Bianchini, but it is very unlikely
that an object which is so prominent when near the terminator was not
often remarked before this.
ARCHYTAS.--A bright ring-plain, 21 miles in diameter, on the edge of the
Mare Frigoris, due N. of the Alpine Valley, with regular walls rising
about 5000 feet above the interior on the N.W., and about 4000 feet on
the opposite side. It has a very bright central mountain. Several spurs
radiate from the wall on the S., and a wide valley, flanked by lofty
heights, forming the S.W. boundary of W.C. Bond, originates on the N
side. There is also a crater-rill running towards the N.W. On the Mare,
S.W. of Archytas, is a somewhat smaller ring-plain, Archytas A (called by
Schmidt, PROTAGORAS), with lofty walls and a central hill.
CHRISTIAN MAYER.--A prominent rhomboidal-shaped ring-plain, 18 miles in
diameter, associated on every side, except the N., with a number of
irregular inconspicuous enclosures. It has a central peak. Madler
discovered two delicate short clefts, both running from N.W. to S.E., one
on the W. and the other on the E. of this formation.
W.C. BOND.--A great enclosed plain of rhomboidal shape on the N. of
Archytas, the bright ring-plain Timaeus standing near its E. corner, and
another conspicuous but much smaller enclosure with a smaller crater W.
of it on the floor at the opposite angle. The interior, which is covered
with rows of hillocks, is very noteworthy at sunrise.
BARROW.--There are few more striking or beautiful objects at sunrise than
this, mainly because of the peculiar shape of its brilliant border and
the remarkable shadows of the lofty peaks on its western wall. There is a
notable narrow gap in the rampart on the W., which appears to extend to
the level of the floor. The walls, especially on the S., are very
irregular, and include two large deep craters and some minor depressions.
If the formation is observed when its E. wall is on the morning
terminator, a fine view is obtained of the remarkable crater-row which
winds round the N. side of Goldschmidt. Barrow is about 40 miles in
diameter. According to Schmidt, there is one crater in the interior, a
little S.E. of the centre.
SCORESBY.--A much fore-shortened deep ring-plain, 36 miles in diameter,
between Barrow and the limb. It has a central mountain with two peaks,
which are very difficult to detect.
CHALLIS.--A ring-plain adjoining Scoresby on the N.E. It is of about the
same size and shape.
MAIN.--A very similar formation, on the N. of the last, much too near the
limb to be well observed.
SECOND QUADRANT
EAST LONGITUDE 0 deg. TO 20 deg.
MURCHISON.--A considerable ring-plain about 35 miles across on the E.,
where it abuts on Pallas. It is a pear-shaped formation, bounded on the
N. by a mountainous region, and gradually diminishes in width towards the
S.E., on which side it is open to the plain. The walls are of no great
altitude, but, except on the N.W., are very bright. At the S. termination
of the W. wall there is an exceedingly brilliant crater, Murchison A,
five miles in diameter and some 3000 feet deep; adjoining which on the
N.W. is an oval depression and a curious forked projection from the
border. The only objects visible in the interior are a few low ridges on
the E. side, and a number of long spurs running out from the wall on the
N. towards the centre of the floor. Murchison A is named CHLADNI by
Lohrmann.
PALLAS.--A fine ring-plain, about 32 miles in diameter, forming with
Murchison an especially beautiful telescopic object under suitable
illumination. Its brilliant border, broken by gaps on the W., where it
abuts on Murchison, has a bright crater on the N.E., from which,
following the curvature of the wall, and just below its crest, runs a
valley in an easterly direction. There is a large bright central mountain
on the floor, with a smaller elevation to the S. of it, and a ridge
extending from the N. wall to near the centre. On the W., a section of
the border is continued in a N. direction far beyond the limits of the
formation; and on the S. it is connected with a small incomplete ring; on
the E. of which, near the foot of the wall, is a somewhat smaller and
much duskier enclosure.
BODE.--A brilliant ring-plain, 9 miles in diameter, situated on the N.
side of Pallas. Its walls rise about 5000 feet above the interior, which
is considerably depressed, and includes, according to Schmidt and Webb, a
mountain or ridge. There are two parallel valleys on the W., which are
well worth examination.
SOMMERING.--An incomplete ring-plain, 17 miles in diameter, situated on
the lunar equator. It has rather low broken walls and a dark interior.
SCHROTER.--A somewhat larger formation, with a border wanting on the S.
Schmidt draws a considerable crater on the S.W. side of the floor. It was
in the region north of this object, which abounds in little hills and low
ridges, that in the year 1822 Gruithuisen discovered a very remarkable
formation consisting of a number of parallel rows of hills branching out
(like the veins of a leaf from the midrib) from a central valley at an
angle of 45 deg., represented by a depression between two long ridges
running from north to south. The regularly arranged hollows between the
hills and the longitudinal valley suggested to his fertile imagination
that he had at last found a veritable city in the moon--possibly the
metropolis of Kepler's _Subvolvani_, who were supposed to dwell on that
hemisphere of our satellite which faces the earth. At any rate, he was
firmly convinced that it was the work of intelligent beings, and not due
to natural causes. This curious arrangement of ridges and furrows, which,
according to Webb, measures about 23 miles both in length and breadth,
is, owing to the shallowness of the component hills and valleys, a very
difficult object to see in its entirety, as it must be viewed when close
to the terminator, and even then the sun's azimuth and good definition do
not always combine to afford a satisfactory glimpse of its ramifications.
M. Gaudibert has given a drawing of it in the _English Mechanic_, vol.
xviii. p. 638.
GAMBART.--A regular ring-plain, 16 miles in diameter, with a low border
and without visible detail within; situated nearly on the lunar equator,
about 130 miles S.S.W. of Copernicus, at the N.W. edge of a very hilly
region. A prominent pear-shaped mountain, with a small crater upon it,
stands a short distance on the S.W., and further in the same direction, a
large bright crater with two much smaller craters on the N. of it. The
rough hilly district about midway between Copernicus and Gambart is
remarkable for its peculiar dusky tone and for certain small dark spots,
first seen by Schmidt, and subsequently carefully observed by Dr. Klein.
The noteworthy region where these peculiar features are found represents
an area of many thousand square miles, and must resemble a veritable
_Malpais_, covered probably with an incalculable number of craters,
vents, cones, and pits, filled with volcanic _debris_. It is among
details of this character that the true analogues of some terrestrial
volcanoes must be looked for. Under a low angle of illumination the
surface presents an extraordinarily rough aspect, well worthy of
examination, but the dusky areas and the black spots can only be
satisfactorily distinguished under a somewhat high sun. I have, however,
seen them fairly well when the W. wall of Reinhold was on the morning
terminator.
MARCO POLO.--A small and very irregularly-shaped enclosure (difficult to
see satisfactorily) on the S. flank of the Apennines. It is hemmed in on
every side by mountains.
ERATOSTHENES.--A noble ring-plain, 38 miles in diameter; a worthy
termination of the Apennines. The best view of it is obtained under
morning illumination when the interior is about half-filled with shadow.
At this phase the many irregular terraces on the inner slope of the E.
wall (which rises at one peak 16,000 feet above an interior depressed
8000 feet below the Mare Imbrium) are seen to the best advantage. The
central mountain is made up of two principal peaks, nearly central, from
which two bright curved hills extend nearly up to the N.W. wall,--the
whole forming a V-shaped arrangement. On the S. there is a narrow break
in the wall, and the S.W. section of it seems to overlap and extend some
distance beyond the S.E. section. The border on the S.W. is remarkable
for the great width of its _glacis_. Eratosthenes exhibits a marked
departure from circularity, especially on the E., where the wall consists
of two well-marked linear sections, with an intermediate portion where
the crest for 20 miles or more bends inwards or towards the centre. From
the S.E. flank of this formation extends towards the W. side of Stadius
one of the grandest mountain arms on the moon's visible surface, rising
at one place 9000 feet, and in two others 5000 and 3000 feet respectively
above the Mare Imbrium. If this magnificent object is observed when the
morning terminator falls a little E. of Stadius, it affords a spectacle
not easily forgotten. I have often seen it at this phase when its broad
mass of shadow extended across the well-known crater-row W. of
Copernicus, some of the component craters appearing between the spires of
shade representing the loftiest peaks on the mountain arm. There is a
prominent little crater on the crest of the arm between two of the peaks,
and another on the plain to the west.
STADIUS.--An inconspicuous though a very interesting formation, 43 miles
in diameter, W. of Copernicus, with a border scarcely exceeding 200 feet
in height. Hence it is not surprising that it was for a long time
altogether overlooked by Madler. Except as a known object, it is only
traceable under very oblique illumination, and even then some attention
is required before its very attenuated wall can be followed all round. It
is most prominent on the W., where it apparently consists of a S.
extension of the Eratosthenes mountain-arm, and is associated with a
number of little craters and pits. This is succeeded on the S.W. by a
narrow strip of bright wall, and on the S. by a section made up of a
piece of straight wall and a strip curving inwards, forming the S. side.
On the E. the border assumes a very ghostly character, and appears to be
mainly defined by rows of small depressions and mounds. On the N.E., N.,
and N.W. it is still lower and narrower; so much so, that it is only for
an hour or so after sunrise or before sunset that it can be traced at
all. On every side, with the exception of the curved piece on the S., the
wall consists of linear sections. The interior contains a great number of
little craters and very low longitudinal mounds. Ten craters are shown in
Beer and Madler's map. Schmidt only draws fifteen, though in the text
accompanying his chart he says that he once counted fifty. In the
monograph published in the _Journal_ of the Liverpool Astronomical
Society (vol. v. part 8), forty-one are represented. They appear to be
rather more numerous on the S. half of the floor than elsewhere. Just
beyond the limits of the border on the N., is a bright crater with a much
larger obscure depression on the W. of it. The former is surrounded by a
multitude of minute craters and crater-cones, which are easily seen under
a low sun. Though almost every trace of Stadius disappears under a high
light, I have had little difficulty in seeing portions of the border and
some of the included details when the morning terminator had advanced as
far as the E. wall of Herodotus, and the site was traversed by
innumerable light streaks radiating from Copernicus. At this phase the
bright crater, just mentioned, on the N. edge of the border was tolerably
distinct.
COPERNICUS.--This is without question the grandest object, not only on
the second Quadrant, but on the whole visible superficies of the moon. It
undoubtedly owes its supremacy partly to its comparative isolation on the
surface of a vast plain, where there are no neighbouring formations to
vie with it in size and magnificence, but partly also to its favourable
position, which is such, that, though not central, is sufficiently
removed from the limb to allow all its manifold details to be critically
examined without much foreshortening. There are some other formations,
Langrenus and Petavius, for example, which, if they were equally well
situated, would probably be fully as striking; but, as we see it
Copernicus is _par excellence_ the monarch of the lunar ring-mountains.
Schmidt remarks that this incomparable object combines nearly all the
characteristics of the other ring-plains, and that careful study directed
to its unequalled beauties and magnificent form is of much more value
than that devoted to a hundred other objects of the same class. It is
fully 56 miles in diameter, and, though generally described as nearly
circular, exhibits very distinctly under high powers a polygonal outline,
approximating very closely to an equilateral hexagon. There are, however,
two sections of the crest of the border on the N.E. which are inflected
slightly towards the centre, a peculiarity already noticed in the case of
Eratosthenes. The walls, tolerably uniform in height, are surmounted by a
great number of peaks, one of which on the W., according to Neison,
stands 11,000 feet above the floor, and a second on the opposite side is
nearly as high. Both the inner and outer slopes of this gigantic rampart
are very broad, each being fully 10 miles in width. The outer slope,
especially on the E., is a fine object at sunrise, when its rugged
surface, traversed by deep gullies, is seen to the best advantage. The
terraces and other features on the bright inner declivities on this side
may be well observed when the sun's altitude is about 6 deg. Schmidt,
whose measures differ from those of Neison, estimates the height of the
wall on the E. to be 12,000 feet, and states that the interior slopes
vary from 60 deg. to 50 deg. above, to from 10 deg. to 2 deg. at the
base. The first inclination of 50 deg., and in some cases of 60 deg., is
confined to the loftiest steep crests and to the flanks of the terraces.
There are apparently five bright little mountains on the floor, the most
easterly being rather the largest, and a great number of minute hillocks
on the S.E. quarter. S.W. of the centre is a little crater, and on the
same side of the interior a curious hook-shaped ridge, projecting from
the foot of the wall, and extending nearly halfway across the floor. The
region surrounding Copernicus is one of the most remarkable on the moon,
being everywhere traversed by low ridges, enclosing irregular areas,
which are covered with innumerable craterlets, hillocks, and other minute
features, and by a labyrinth of bright streaks, extending for hundreds of
miles on every side, and varying considerably both in width and
brilliancy.
The notable crater-row on the W., often utilised by observers for testing
the steadiness of the air and the definition of their telescopes, should
be examined when it is on the morning terminator, at which time Webb's
homely comparison, "a mole-run with holes in it," will be appreciated,
and its evident connection with the E. side of Stadius clearly made out.
There is another much more delicate row running closely parallel to this
object; it lies a little W. of it, and extends farther in a northerly
direction.
ARCHIMEDES.--Next to Plato the finest object on the Mare Imbrium. It is
about 50 miles in diameter. The average height of its massive border is
about 4000 feet above the interior, which is only depressed some 500 or
600 feet below the Mare, the highest peak (about 7000 feet) being on the
S.E. The walls are terraced, and include much detail, both within and
without. The most noteworthy features in connection with this formation
are the crater-cones, craterlets, pits, white spots, and light streaks
which figure on the otherwise smooth interior. Mr. T.P. Gray, F.R.A.S.,
of Bedford, who, with praiseworthy assiduity, has devoted more than ten
years to the close scrutiny of these features, Mr. Stanley Williams, and
others, have detected four crater-cones on the E. half of the floor, and
about fifty minute craters and white spots, also probably volcanic vents,
and a very curious and interesting series of light streaks, mostly
traversing the formation from E. to W. A little E. of the centre is a
dusky oval area about 6 miles across, and S.W. of this is another, much
smaller. Under some conditions of illumination the two principal light
markings may be traced over the W. wall, and for some distance on the
plain beyond.
On the southern side of Archimedes is a very rugged mountain region,
extending for more than 100 miles towards the south: on the W. of this
originates a remarkable rill-system, best seen under evening
illumination. The two principal clefts follow a nearly parallel course up
to the face of the Apennines near Mount Bradley, crossing in their way,
almost at right angles, other clefts which run at no great distance from
the E. foot of this range and ramify among the outlying hills. Archimedes
A is a brilliant little ring-plain on the S.E. of Archimedes. It casts an
extraordinary shadow at sunrise, and has a well-marked crater-row on the
E. of it, and two long narrow valleys, one of which appears to be a
southerly extension of the row.
BEER.--A very bright little crater, with an unnamed formation of about
the same size adjoining it on the N., with which is associated a curious
winding ridge that appears to traverse a gap in its N. wall.
TIMOCHARIS.--A fine ring-plain, 23 miles in diameter (the centre of a
minor ray-system). It stands isolated on the Mare Imbrium (below the
level of which it is depressed some 3000 feet), about midway between
Archimedes and Lambert. Its walls, rising about 7000 feet above the
floor, are conspicuously terraced, and on their W. outer slopes exhibit
some remarkable depressions. There is a distinct break on the N., and a
bright little crater on the N.W., connected with the foot of the _glacis_
by a prominent ridge. On the bright central mountain, Schmidt, in 1842,
detected a crater, which is easily seen under a moderately high light.
Timocharis and the neighbourhood, especially the peculiar shape of the
terminator on the E. of the formation, is well worth examination at
sunrise.
PIAZZI SMYTH.--A conspicuous little ring-plain, 5 or 6 miles in diameter,
depressed about 1500 feet below the Mare Imbrium, with a border rising
about 2000 feet above it. With the curious arrangement of ridges, of
which it is the apparent centre, it is a striking object under a low sun.
KIRCH.--A rather smaller object of the same class on the S.E.
PLATO.--This beautiful walled-plain, 60 miles in diameter, with its
bright border and dark steel-grey floor, has, from the time of Hevelius
to the present, been one of the most familiar objects to lunar observers.
In the rude maps of the seventeenth century it figures as the "Lacus
Niger Major," an appellation which not inaptly describes its appearance
under a high sun, when the sombre tone of its apparently smooth interior
is in striking contrast to that of the isthmus on which the formation
stands. It will repay observation under every phase, and though during
the last thirty years no portion of the moon has been more diligently
scrutinised than the floor; the neighbourhood includes a very great
number of objects of every kind, which, not having received so much
attention, will afford ample employment to the possessor of a good
telescope during many lunations.
The border of Plato, varying in height from 3000 to 4000 feet above the
interior, is crowned by several lofty peaks, the highest (7400 feet)
standing on the N. side of the curious little triangular formation on the
E. wall. Those on the W., three in number, reckoning from N. to S., are
respectively about 5000, 6000, and 7000 feet in altitude above the floor.
The circumvallation being very much broken and intersected by passes,
exhibits many distinct breaches of continuity, especially on the S. There
is a remarkable valley on the S.W., which, cutting through the border at
a wide angle, suddenly turns towards the S.E., and descends the slope of
the _glacis_ in a more attenuated form. Another but shorter valley is
traceable at sunrise on the W. On the N.W., the rampart is visibly
dislocated, and the gap occupied by an intrusive mountain mass. This
dislocation is not confined to the wall, but, under favourable
conditions, may be traced across the floor to the broken S.E. border. It
is probably a true "fault." On the N.E., the inner slope of the wall is
very broad, and affords a fine example of a vast landslip.
The spots and faint light markings on the floor are of a particularly
interesting character. During the years 1869 to 1871 they were
systematically observed and discussed under the auspices of the Lunar
Committee of the British Association. Among the forty or more spots
recorded, six were found to be crater-cones. The remainder--or at least
most of them--are extremely delicate objects, which vary in visibility in
a way that is clearly independent of libration or solar altitude; and,
what is also very suggestive, they are always found closely associated
with the light markings,--standing either upon the surface of these
features or close to their edges. Recent observations of these spots with
a 13 inch telescope by Professor W.H. Pickering, under the exceptionally
good conditions which prevail at Arequipa, Peru, have revived interest in
the subject, for they tend to show that visible changes have taken place
in the aspect of the principal crater-cones and of some of the other
spots since they were so carefully and zealously scrutinised nearly a
quarter of a century ago. The gradual darkening of the floor of Plato as
the sun's altitude increases from 20 deg. till after full moon may be
regarded as an established fact, though no feasible hypothesis has been
advanced to account for it.
On the N.E. of Plato is a large bright crater, A; and, extending in a
line from this towards the E., is a number of smaller rings, the whole
group being well worth examination. On the N. there is a winding cleft,
and some short crossed clefts in the rugged surface just beyond the foot
of the wall, which I have seen with a 4 inch achromatic. The region on
the W., imperfectly shown in the maps, includes much unrecorded detail.
On the Mare Imbrium S. of Plato is a large area enclosed by low ridges,
to which Schroter gave the name "Newton." It suggests the idea that it
represents the ruin of a once imposing enclosure, of which the
conspicuous mountain Pico formed a part.
TIMAEUS.--A very bright ring-plain, 22 miles in diameter, with walls
about 4500 feet in height, on the coast-line of the Mare Frigoris, and
associated with the E. side of the great enclosed plain W.C. Bond.
Schmidt shows a double hill, nearly central, and Neison a crater on the
S.W. wall.
BIRMINGHAM.--A large rhomboidal-shaped enclosure, defined by mountain
chains and traversed by a number of very remarkable parallel ridges. It
is situated nearly due N. of Plato on the N. edge of the Mare Frigoris,
and lies on the S.E. side of W.C. Bond, to which it bears a certain
resemblance. This region is characterised by the parallelism displayed by
many formations, large and small. It is more apparent hereabouts than in
any other part of the moon's visible surface. When favourably placed
under a low morning sun, Birmingham is a striking telescopic object.
FONTINELLE.--A fine ring-plain, 23 miles in diameter, on the N. margin of
the Mare Frigoris, N.N.E. of Plato, with a wall rising on the E., 6000
feet above a bright interior. I find its border indistinct and nebulous,
excepting under very oblique light, though three of the little craters
upon it are bright and prominent. One stands on the S., another on the
N.W., and a third on the E. Schmidt shows only the first of these, and
Neison none of them. Fontinelle has a low central mountain which is
easily distinguished. Fontinelle A, an isolated mountain on the S., is
more than 3000 feet high. On the N. there is a curious mountain group,
also of considerable altitude, and on the W. an irregular depression
surrounded by a dusky area. North of Fontinelle, extending towards
Goldschmidt and the limb, Schroter discovered a very wide irregular
valley which he named "J.J. Cassini." It is really nothing more than a
great plain bounded by ridges. At 9 h. October 15, 1888, when Philolaus
was on the morning terminator, I had a fine view of it, and, as regards
its general shape, found that it agreed very closely with Schroter's
drawing.
EPIGENES.--A remarkable ring-plain, about 26 miles in diameter, abutting
on a mountain ridge running parallel to the E. flank of W.C. Bond. It is
a notable object under a low morning sun. There are several elevations on
the floor.
GOLDSCHMIDT.--A great abnormally-shaped enclosure with lofty walls
between Epigenes and the limb. Neison mentions only two crater-pits
within. I have seen the rimmed crater shown by Schmidt on the W. side and
three or four other objects of a doubtful kind.
ANAXAGORAS.--A brilliant ring-plain of regular form, 32 miles in
diameter, adjoining Goldschmidt on the E. It is a prominent centre of
light streaks, some of which traverse the interior of Goldschmidt. On the
north a peak rises to the height of 10,000 feet. There is a long ridge on
the floor, running from E. to W.
GIOJA.--A ring-plain about 26 miles in diameter, near the north pole.
EAST LONGITUDE 20 deg. TO 40 deg.
REINHOLD.--A prominent ring-plain, 31 miles in diameter, with a lofty
border, rising at a peak on the W. to more than 9000 feet above the
floor. Its shape on the W. is clearly polygonal, the wall consisting of
three rectilineal sections, and on the E. it is made up of two straight
sections connected by a curved section. The inner slope includes a
remarkably distinct and regular terrace, the E. portion of which is well
seen when the interior is about half illuminated by the rising sun. At
this phase also the great extent of the _glacis_ on the S.W., and the
deep wide gullies traversing it on the E. are observed to the best
advantage. The central mountain, though of considerable size, is not
prominent. Close to Reinhold on the N.W. stands a noteworthy little
formation with a low and partially lineal wall, exhibiting a gap on the
north. There is a distinct crater on the S. side of its floor.
GAY-LUSSAC.--A very interesting ring-plain, 15 miles in diameter,
situated in the midst of the Carpathian Highlands N. of Copernicus, with
a smaller but brighter and deeper formation (Gay-Lussac A) on the S.W. of
it, and a conspicuous little crater, not more than 2 or 3 miles in
diameter, between the two. The interior of Gay-Lussac is traversed by two
coarse clefts, lying nearly in a meridional direction. The more easterly
runs from the foot of the S. wall, near the little crater just mentioned,
across the floor to the low N. border, which it apparently cuts through,
and extends for some distance beyond, terminating in a great oval
expansion. The other, which is not shown in the maps, is closely parallel
to it, and can be traced up to the N. border, but not farther. Schmidt
represents the first as a crater-row, which it probably is, as it varies
considerably in width. From the S.E. side of the formation extends a long
cleft, terminating at the end of a prominent spur from the S. side of the
Carpathians. There are also two remarkable rill-like valleys, commencing
on the N. of Gay-Lussac A, which curve round the W. side of Gay-Lussac.
HORTENSIUS.--This brilliant crater, about 10 miles in diameter, is
remarkable for its depth, and as being a ray-centre surrounded by a
nimbus of light. It has a central mountain, and Schmidt shows a minute
crater on the outer slope of the S. wall. The former is a test object.
MILICHIUS.--Is situated on the N.N.E. of Hortensius. It is fully as
bright, but rather smaller. Its floor, apparently devoid of detail, is
considerably depressed below the surrounding surface.
TOBIAS MAYER.--Like Gay-Lussac, a noteworthy ring-plain associated with
the Carpathian Mountains. It is 22 miles in diameter, and has a wall
which rises on the W. to a height of nearly 10,000 feet above the floor;
on the latter there is a conspicuous central mountain, and on the E. side
a crater, and some little hills. Schmidt shows a smaller crater on the W.
side, which I have not seen. Adjoining the formation on the W. is a ring-
plain of about one-fourth its area, which is a bright object. Tobias
Mayer and the neighbouring Carpathians form an especially beautiful
telescopic picture at sunrise.
KUNOWSKY.--An inconspicuous ring-plain, about 11 miles in diameter,
standing in a barren region in the Mare Procellarum, W.S.W. of Encke. The
central mountain is tolerably distinct.
ENCKE.--A regular ring-plain, 20 miles in diameter, with a comparatively
low border, nowhere rising more than 1800 feet above the interior, which
is depressed some 1000 feet below the surrounding Oceanus Procellarum. A
lofty ridge traverses the floor from S. to N., bifurcating before it
reaches the N. wall. There is a bright crater on the W. wall, and a
depression on the opposite wall, neither of which, strange to say, is
shown on the maps. Encke is encircled by ridges, which, when it is on the
morning terminator, combine to make it resemble a large crater surrounded
by a vast mountain ring.
KEPLER.--One of the most brilliant objects in the second quadrant,--a
ring-plain about 22 miles in diameter, with a lofty border; a peak on the
E. attaining an altitude of 10,000 feet above the surface. The wall is
much terraced, especially the outer slope on the W., where a narrow
valley is easily traceable. Though omitted from the maps, there is a
prominent circular depression on the W. border, which forms a distinct
notch thereon at sunrise. On the N., the wall exhibits a conspicuous
gap. There is a central hill on the floor. Immediately E. of Kepler is a
bright plateau, bounded on the N. by a very straight border, with two
small craters on its edge. Both these objects are incomplete on the N.,
as if they had been deformed by a "fault," which has apparently affected
the N. end of Kepler also. Kepler is the centre of one of the most
extended systems of bright streaks on the moon's visible surface.
BESSARION.--A bright little ring-plain, about 6 miles in diameter, in the
Oceanus Procellarum N. of Kepler. There is a smaller and still brighter
companion on the N. (Bessarion E), standing on a light area. Bessarion
has a minute central hill, difficult to detect.
PYTHEAS.--A small rhomboidal-shaped ring-plain, 12 miles in diameter,
standing in an isolated position on the Mare Imbrium between Lambert and
Gay-Lussac. Its bright walls, rising about 2500 feet above the Mare, are
much terraced within, especially on the E. There is a bright little
crater on the N. outer slope, with a short serpentine ridge running up to
it from the region S. of Lambert, and another winding ridge extending
from the S. wall to the E. of two conspicuous craters, standing about
midway between Pytheas and Gay-Lussac. The former bears a great
resemblance to the ridge N. of Madler, and, like this, appears to
traverse the N. border. The interior of Pytheas, which is depressed more
than 2000 feet below the Mare, includes a brilliant central peak.
LAMBERT.--A ring-plain, 17 miles in diameter, presenting many noteworthy
features. The crest of its border stands about 2000 feet above the Mare
Imbrium, and more than double this height above the interior. The wall is
prominently terraced both within and without; the outer slope on the W.
exhibiting at sunrise a nearly continuous valley running round it. When
near the morning terminator, the region on the N. is seen to be traversed
by some very remarkable ridges and markings; one cutting across the N.
wall appears to represent a "fault." On the S. is a large polygonal
enclosure formed by low ridges. On the W., towards Timocharis, is a
brilliant mountain 3000 feet high, a beautiful little object under a low
sun.
LEVERRIER.--The more westerly of a pair of little ring-plains on the N.
side of the Mare Imbrium, and S.W. of the Laplace promontory. It is about
10 miles in diameter, with walls rising some 1500 feet above the Mare,
and more than 6000 feet above the interior, which seems to be without a
central mountain or other features. Schmidt shows the crater on the N.
rim and another on the S.E. slope, both of which are omitted by Neison,
though they are easy objects when Helicon is on the morning terminator.
About 20 miles on the S.E. there is a very bright little crater on a
faint light area.
HELICON.--The companion ring-plain on the E. It is 13 miles in diameter,
and is very similar, though not quite so deep. There is a crater on the
S.E. wall, and, according to Neison, another on the outer slope of the N.
border. Webb records a central crater. If Helicon is observed when on the
morning terminator, it will be seen to be traversed by a curved ridge
which cuts through the walls, and runs up to a bright crater S.E. of
Leverrier. It appears to be a "fault," whose "downthrow," though slight,
is clearly indicated by an area of lower ground on the E. There is a
great number of small craters in the neighbourhood of this formation.
EULER.--The most easterly of the row of great ring-plains, which,
beginning on the W. with Autolycus, and followed by Archimedes,
Timocharis, and Lambert, extends almost in a great circle from the N.W.
to the S.E. side of the Mare Imbrium. It is about 19 miles in diameter,
and is surrounded by terraced walls, which, though of no great height
above the Mare, rise 6000 feet above the floor. There is a distinct
little gap in the S. wall, easily glimpsed when it is close to the
morning terminator, which probably represents a small crater. Euler has a
bright central mountain, and is a centre of white silvery streaks.
BRAYLEY.--A very conspicuous little ring-plain E.S.E. of Euler, with two
smaller but equally brilliant objects of the same class situated
respectively E. and W. of it.
DIOPHANTUS.--Forms with Delisle, its companion on the N., a noteworthy
object. It is about 13 miles in diameter, with a wall, which has a
distinct break in its continuity on the N., rising about 2500 feet above
the Mare. A rill-valley runs from the E. side of the ring towards the W.
face of a triangular-shaped mountain on the E. of a line joining the
formation with Delisle. North are three bright little craters in a line,
the middle one being much the largest. From the most easterly of these
objects a light streak may be traced under a high sun, extending for many
miles to another small crater on the N.W. of Diophantus, and expanding at
a point due N. of the formation into a spindle-shaped marking. At
sunrise, the W. portion of the streak has all the appearance of a cleft,
with a branch about midway running to the S. side of Delisle. Under the
same phase a broad band of shadow extends from the N.E. wall to the
triangular mountain just mentioned, representing a very sudden drop in
the surface--resembling on a small scale the well-known "railroad" E. of
Thebit. Diophantus has no central mountain.
DELISLE.--A larger and more irregularly-shaped object than the last, 16
miles in diameter, with loftier and more massive walls, and an extensive
but ill-defined central hill. There is an evident break in the northern
border. A triangular mountain on the S.E. and a winding ridge running up
to the N. wall are prominent features at sunrise, as are also the
brilliant summits of a group of hills some distance to the E.N.E.
CARLINI.--A small but prominent and deep little crater about 5 miles in
diameter on the Mare Imbrium about midway between Lambert and the Sinus
Iridum. There are many faint light streaks in the vicinity, one of which
extends from Carlini to Bianchini, on the edge of the Sinus,--a distance
of 300 miles. Schmidt shows a central peak.
CAROLINE HERSCHEL.--A bright and very deep ring-plain about 8 miles in
diameter on the Mare Imbrium, some distance E.N.E. of the last. On the
S.E. lies a larger crater, Delisle B, which has a small but obvious
crater on its N. rim, and casts a very prominent shadow at sunrise.
Caroline Herschel stands on a long curved ridge running N.E. from Lambert
towards the region E. of Helicon, and, according to Schmidt, has a
central peak. On the E. is a bright mountain with two peaks; some
distance N. of which is a large ill-defined white spot, with another spot
of a similar kind on the W. of it, nearly due N. of Caroline Herschel.
GRUITHUISEN.--This ring-plain, 10 miles in diameter, is situated on the
Mare Imbrium on the N.E. of Delisle. It is associated with a number of
ridges trending towards the region N. of Aristarchus and Herodotus.
THE LAPLACE PROMONTORY.--A magnificent headland marking the extreme
western extremity of the finest bay on the moon's visible surface, the
Sinus Iridum; above which it towers to a height of 9000 feet or more,
projecting considerably in front of the line of massive cliffs which
define the border of the Sinus, and presenting a long straight face to
the S.E. Near its summit are two large but shallow depressions, the more
easterly having a very bright interior. At a lower level, almost directly
below the last, is a third depression. All three are easy objects under a
low sun. The best view of the promontory and its surroundings is obtained
when the E. side of the bay is on the morning terminator. Its prominent
shadow is traceable for many days after sunrise.
THE HERACLIDES PROMONTORY.--The less lofty but still very imposing
headland at the E. end of the Sinus Iridum, rising more than 4000 feet
above it. It consists of a number of distinct mountains, forming a
triangular-shaped group running out to a point at the S.W. extremity of
the bay, and projecting considerably beyond the shore-line. There is a
considerable crater on the E. side of the headland, not visible till a
late stage of sunrise. It is among the mountains composing this
promontory that some ingenuity and imagination have been expended in
endeavouring to trace the lineaments of a female face, termed the "Moon-
maiden."
BIANCHINI.--A fine ring-plain, about 18 miles in diameter, on the N.E.
side of the Sinus Iridum, surrounded by the lofty mountains defining the
border of the bay. Its walls, which are prominently terraced within, rise
about 7000 feet on the E., and about 8000 feet on the W. above the floor,
which includes a prominent ridge and a conspicuous central mountain.
There is a distinct crater on the S. wall, not shown in the maps. Between
this side of the formation and the bay is a number of hills running
parallel to the shore-line: these, with the intervening valleys, will
repay examination at sunrise.
MAUPERTUIS.--A great mountain enclosure of irregular shape, about 20
miles in diameter, in the midst of the Sinus Iridum highlands, N. of
Laplace. The walls are much broken by passes, and the interior includes
many hills and ridges.
CONDAMINE.--A rhomboidal-shaped ring-plain, about 23 miles in diameter,
N. of Maupertuis, with lofty walls, especially on the E., where they rise
some 4000 feet above the interior. There are three large depressions on
the outer N.W. slope, and at least three minute craters on the crest of
the wall just above. Though neither Neison nor Schmidt draw any detail
thereon, there is a prominent ridge on the N. side of the floor, and a
low circular hill on the S. On the S.E. four long ridges or spurs radiate
from the wall, and on the N.E. are three remarkable square-shaped
enclosures. On the edge of the Mare Frigoris, N.W. of Condamine, are many
little craters with bright rims and a distinct short cleft, running
parallel to the coast-line. The winding valleys in the region bordering
the Sinus Iridum, and other curious details, render this portion of the
moon's surface almost unique.
BOUGUER.--A bright regular little ring-plain, about 8 miles in diameter,
N. of Bianchini.
J.F.W. HERSCHEL.--A vast enclosed plain, about 90 miles across, bounded
on the W. by a mountain range, which here defines the E. side of the Mare
Frigoris, on the S. by massive mountains, and on the other sides by a
lofty but much broken wall, intersected by many passes. Within is a large
ring-plain, nearly central, and a large number of little craters and
crater-pits. The floor is traversed longitudinally by many low ridges,
lying very close together, which at sunrise resemble fine grooves or
scratches of irregular width and depth.
HORREBOW.--A ring-plain of remarkable shape, resembling the analemma
figure, standing at the S. end of the mountain range bounding J.F.W.
Herschel on the W. Schmidt shows a crater on the W. wall, near the
constriction on this side, and a second at the foot of the slope of the
E. wall.
PHILOLAUS.--A ring-plain 46 miles in diameter, on the N.E. of Fontinelle.
Its bright walls rise on the W. to a height of nearly 12,000 feet above
the floor (on which there is a conspicuous central mountain), and exhibit
many prominent terraces. Philolaus is partially encircled, at no great
distance, by a curved ridge, on which will be found a number of small
craters.
ANAXIMINES.--A much foreshortened ring-plain, about 66 miles in diameter,
on the E. of Philolaus. One peak on the E. is nearly 8000 feet in height.
Schmidt shows four craters on the W. side of the floor, and a fifth on
the S.E. side. There is a bright streak in the interior, which extends
southwards for some distance across the Mare Frigoris.
EAST LONGITUDE 40 deg. TO 60 deg.
REINER.--A regular ring-plain, 21 miles in diameter, in the Mare
Procellarum, S.S.E. of Marius, with a very lofty border terraced without
and within, and a minute but conspicuous mountain standing at the N. end
of a ridge which traverses the uniformly dark floor in a meridional
direction. A long ridge extends some way towards the S. from the foot of
the S. wall, and at some distance in the same direction lie six ill-
defined white spots of doubtful nature. On the E.N.E. there is a large
white marking, resembling a "Jew's harp" in shape, and farther on,
towards the E., a number of very remarkable ridges. On the W. will be
found many bright little craterlets. A ray from Kepler extends almost up
to the W. wall of Reiner.
MARIUS.--A very noteworthy ring-plain, 27 miles in diameter, in the
Oceanus Procellarum, E.N.E. of Kepler, with a bright border rising about
4000 feet above the interior, which is of an uneven tone. The rampart
exhibits some breaks, especially on the S. The outer slope on the W. is
traversed by a fine deep valley, distinctly marked when the opposite side
is on the morning terminator. It originates on the S.W. at a prominent
crater situated a little below the crest of the wall, and, following its
curvature, runs out on to the plain near a large mountain just beyond the
foot of the N. border. In addition to the crater just mentioned, there
are two smaller ones below the summit of the S. wall, and a small
circular depression on the S.E. wall. Mr. W.H. Maw, F.R.A.S., has seen,
with a 6 inch Cooke refractor, a bright marking at the N. extremity of
the ring, which, when examined with a Dawes' eyepiece, resembled an
imperfect crater. The floor includes at least four objects--(1) A crater
on the N.W., standing on a circular light area; (2) a white spot a little
S. of the centre; (3) a smaller white spot S.E. of this; (4) another,
near the inner foot of the S.W. wall. Marius is an imposing object under
oblique illumination, mainly because of the number of ridges by which it
is surrounded. I have frequently remarked at sunrise that the surface on
the W., and especially the outer slope of the rampart, is of a decided
brown or sepia tint, similar to that which has already been noticed with
respect to Geminus and its vicinity, viewed under like conditions.
Schmidt in 1862 discovered a long serpentine cleft some distance N. of
Marius, which has not been seen since.
ARISTARCHUS.--The brightest object on the moon, forming with Herodotus (a
companion ring-plain on the E.), and its remarkable surroundings, one of
the most striking objects which the telescope has revealed on the visible
surface, and one requiring much patient observation before its manifold
details can be fully noted and duly appreciated. Its border rises 2000
feet above the outer surface on the W., but towers to more than double
this height above the glistening floor. No lunar object of its moderate
dimensions (it is only about 29 miles in diameter) has such conspicuously
terraced walls, or a greater number of spurs and buttresses; which are
especially prominent on the S. A valley runs round the outer slope of the
W. wall, very similar to that found in a similar position round Marius.
There is also a distinct valley on the brilliant inner slope of the E.
wall, below its crest. It originates at a bright little crater, and is
traceable round the greater portion of the declivity. Under a moderately
high sun, an oval area, nearly as large and fully as brilliant as the
central mountain, is seen on this inner slope. It is bordered on either
side by bands of a duskier hue, which probably represent shallow
transverse valleys. From its dazzling brilliancy it is very difficult to
observe the interior satisfactorily. In addition, however, to the central
mountain, there is a crater on the N.W. side of the floor. On the S. side
of Aristarchus is a large dusky ring some 10 miles in diameter, connected
by ridges with the spurs from the wall, and on the S.E., close to the
foot of the slope, is another smaller ring of a like kind.
HERODOTUS.--This far less brilliant but equally interesting object is
about 23 miles in diameter, and is not so regular in shape as
Aristarchus. Its W. wall rises at one point more than 4000 feet above the
very dusky floor. Except on the S.W. and N.E., the border is devoid of
detail. On the S.W. three little notches may be detected on its summit,
which probably represent small craters, while on the opposite side, on
the inner slope, a little below the crest, is a large crater, easily
seen. Both the E. and W. sections of the wall are prolonged towards the
S. far beyond the limits of the formation. These rocky masses, with an
intermediate wall, are very conspicuous under oblique illumination, that
on the S.W. being especially brilliant. On the N. there is a gap through
which the well-known serpentine cleft passes on to the floor. Between the
N.W. side of Herodotus and Aristarchus is a large plateau, seen to the
best advantage when the morning terminator lies a little distance E. of
the former. It is traversed by a T-shaped cleft which communicates with
the great serpentine cleft and extends towards the S. end of Aristarchus,
till it meets a second cleft (forming the upper part of the T) running
from the S.E. side of this formation along the W. side of Herodotus. The
great serpentine cleft, discovered by Schroter, October 7, 1787, is in
many respects the most interesting object of its class. It commences at
the N. end of a short wide valley, traversing mountains some distance
N.E. of Herodotus, as a comparatively delicate cleft. After following a
somewhat irregular course towards the N.W. for about 50 miles, and
becoming gradually wider and deeper, it makes a sudden turn and runs for
about 10 miles in a S.W. direction. It then changes its course as
abruptly to the N.W. again for 3 or 4 miles, once more turns to the S.W.,
and, as a much coarser chasm, maintains this direction for about 20
miles, till it reaches the S.E. edge of a great mountain plateau N. of
Aristarchus, when it swerves slightly towards the S., becoming wider and
wider, up to a place a few miles N. of Herodotus, where it expands into a
broad valley; and then, somewhat suddenly contracting in width, and
becoming less coarse, enters the ring-plain through a gap in the N. wall,
as before mentioned. I always find that portion of the valley in the
neighbourhood of Herodotus more or less indistinct, though it is broad
and deep. This part of it, unless it is observed at a late stage of
sunrise, is obscured by the shadow of the mountains on the border of the
plateau. Gruithuisen suspected a cleft crossing the region embraced by
the serpentine valley, forming a connection between its coarse southern
extremity and the long straight section. This has been often searched
for, but never found. It may exist, nevertheless, for in many instances
Gruithuisen's discoveries, though for a long time discredited, have been
confirmed. The mountain plateau N. of Aristarchus deserves careful
scrutiny, as it abounds in detail and includes many short clefts.
HARBINGER, MOUNTAINS.--A remarkable group of moderate height, mostly
extending from the N.W. towards Aristarchus. They include a large
incomplete walled-plain about 30 miles in diameter, defined on the W. by
a lofty border, forming part of a mountain chain, and open to the south.
This curious formation has many depressions in connection with its N.W.
edge. On the N. of it there is a crater-row and a very peculiar zig-zag
cleft. The region should be observed when the E. longitude of the morning
terminator is about 45 deg.
SCHIAPARELLI.--A conspicuous formation, about 16 miles in diameter,
between Herodotus and the N.E. limb, with a border rising nearly 2000
feet above the Mare, and about 1000 more above the floor, on which
Schmidt shows a central hill.
WOLLASTON.--A small bright crater on the Mare N. of the Harbinger
Mountains, surpassed in interest by a remarkable formation a few miles S.
of it, Wollaston B, an object of about the same size, but which is
associated with a much larger enclosure, resembling a walled-plain, lying
on the N. side of it. This formation has a lofty border on the W.,
surmounted by two small craters. The wall is lower on the E. and exhibits
a gap. There is a central hill, only visible under a low sun. About
midway between Wollaston and this enclosure stands a small isolated
triangular mountain. From a hill on the E. runs a rill valley to the more
westerly of a pair of craters, connected by a ridge, on the S.E. of
Wollaston B.
MAIRAN.--A bright ring-plain of irregular shape, 25 miles in diameter, on
the E. of the Heraclides promontory. The border, especially on the E.,
varies considerably in altitude, as is evident from its shadow at
sunrise; at one peak on the W. it is said to attain a height of more than
15,000 feet above the interior. There is a very minute crater on the
crest of the S. wall, down the inner slope of which runs a rill-like
valley. About halfway down the inner face of the E. wall are two other
small craters, connected together by a winding valley. These features may
be seen under morning illumination, when about one-fourth of the floor is
in sunlight. Schroter is the only selenographer who gives Mairan a
central mountain. In this he is right. I have seen without difficulty on
several occasions a low hill near the centre. The formation is surrounded
by a number of conspicuous craters and crater-pits. On the N. there is a
short rill-like valley, and another, much coarser, on the S.
SHARP.--A ring-plain somewhat smaller than the last, on the E. of the
Sinus Iridum, from the coast-line of which it is separated by lofty
mountains. There is a distinct crater at the foot of its N.E. wall, and a
bright central mountain on the floor. On the N. is a prominent enclosure,
nearly as large as Sharp itself; and on the N.E. a brilliant little ring-
plain, A, about 8 miles in diameter, connected with Sharp, as Madler
shows, by a wide valley.
LOUVILLE.--A triangular-shaped formation on the E. of a line joining
Mairan and Sharp. It is hemmed in by mountains, one of which towers 5000
feet above its dusky floor.
FOUCAULT.--A bright deep ring-plain, about 10 miles in diameter, lying E.
of the mountains fringing the Sinus Iridum, between Bianchini and
Harpalus. A very lofty peak rises near its N. border, and, according to
Neison, it has a distinct central mountain, though neither Madler or
Schmidt show any detail within.
HARPALUS.--A conspicuous ring-plain, about 14 miles in diameter, on the
N.E. of the last, with a floor sinking 13,000 feet below the surrounding
surface. As the cubic contents of the border and _glacis_ are quite
inadequate to account for it, we may ask, what has become of the material
which presumably once filled this vast depression? Harpalus has a bright
central mountain.
SOUTH.--On the W. and S., the boundaries of this extensive enclosure are
merely indicated by ridges, which nowhere attain the dignity of a wall.
On the N., the edge of a tableland intersected by a number of valleys
define its limits, and on the E. a border forming also the W. side of
Babbage. The interior is traversed by a number of longitudinal hills, and
includes two bright little heights, drawn by Schmidt as craters.
BABBAGE.--A still larger enclosed area, adjoining South on the E., and
containing a considerable ring-plain near its W. border. It is a fine
telescopic object at sunrise, the interior being crossed by a number of
transverse markings representing ridges. These are very similar in
character (but much coarser) to those found on the floor of J.F.W.
Herschel. The curious detail on the E. wall is also worth examination at
this phase.
ROBINSON.--A bright and very deep little ring-plain, about 12 miles in
diameter, on a plateau N. of South. Schmidt shows a crater on the W.
border, and two others at the foot of the N. and E. borders respectively.
ANAXIMANDER.--A fine but much foreshortened ring-plain, 39 miles in
diameter, abutting on the E. side of J.F.W. Herschel. It has a large
crater on its W. border, which is common to the two formations, and a
very prominent crater, both on the S. and N. The barrier on the S.W.
rises to a height of nearly 10,000 feet. Schmidt shows a crater and other
details on the floor.
EAST LONGITUDE 60 deg. TO 90 deg.
LOHRMANN.--This ring-plain, with Hevel and Cavalerius on the N. of it, is
a member of a linear group, which, but for its propinquity to the limb,
would be one of the most imposing on the moon's surface. Lohrmann, about
28 miles in diameter, is surrounded by a bright wall, which, to all
appearance, is devoid of detail. Two prominent ridges, with a fine
intervening valley, connect it with the N. end of Grimaldi. It has a
large but not conspicuous central mountain. On the rugged surface,
between the ring-plain and the E. edge of the Oceanus Procellarum, lies a
very interesting group of crossed clefts, some of which run from N.E. to
S.W., and others from N.W. to S.E. Three of the latter proceed from
different points in a coarse valley extending from W. to E., and cross
the ridges just mentioned. They follow a parallel course, and terminate
on the S. side of a crater-row, consisting of three bright craters
ranging in a line parallel to the coarse valley. On the N. side of these
objects, and tangential to them, is another cleft, which traverses the W.
and E. walls of Lohrmann, and, crossing the region between it and
Riccioli, terminates apparently at the W. wall of the latter formation.
No map shows this cleft, though it is obvious enough; and, when the E.
wall of Hevel is on the morning terminator, the notches made by it in the
border of Lohrmann are easily detected. Capt. Noble, F.R.A.S., aptly
compares two of the crossed clefts to a pair of scissors, the craters at
which they terminate representing the oval handles. On the grey surface
of the Mare W. of Lohrmann is the bright crater Lohrmann A, from which,
running N., proceeds a rill-like valley ending at a large white spot,
which has a glistening lustre under a high light.
HEVEL.--A great walled-plain, 71 miles in diameter, adjoining Lohrmann on
the N., with a broad western rampart, rising at one peak to a height
above the interior of nearly 6000 feet, and presenting a steep bright
face to the Oceanus Procellarum. There are three prominent craters near
its crest, and one or two breaks in its continuity. It is not so lofty
and is more broken on the E., where three conspicuous craters stand on
its inner slope. The floor is slightly convex, and includes a triangular
central mountain, on which there is a small crater. The S. half of the
interior is crossed by four clefts: (l) running from a little crater N.
of the central mountain, on the W. side of it, to a hill at the foot of
the S.W. wall; (2) originating near the most southerly of the three
craters on the inner slope of the E. wall, and crossing 1, terminates at
the foot of the W. wall; (3) has the same origin as 2, crosses 1, and,
passing over a craterlet W. of the central mountain, also runs up to the
W. wall at a point considerably N. of that where 2 joins the latter; (4)
runs from the craterlet just mentioned to the W. end of 2.
CAVALERIUS.--The most northerly member of the linear chain, a ring-plain,
41 miles in diameter, with terraced walls rising about 10,000 feet above
the floor. Within there is a long central mountain with three peaks.
Under a high light the region on the W. is seen to be crossed by broad
light streaks.
OLBERS.--A large ring-plain, 41 miles in diameter, near the limb, N.E. of
Cavalerius. Though a very distinct formation, it is difficult to see its
details except under favourable conditions of libration. It has a large
crater on its W. wall, a smaller one on the E., and a third on the N. The
floor includes a central mountain, and, according to Schmidt, four
craters. He also shows a crater-rill on the W. wall, N. of the large
crater thereon. Olbers is the origin of a fine system of light rays.
GALILEO.--A ring-plain, about 9 miles in diameter, N.E. of Reiner,
associated with ridges, some of which extend to the "Jew's Harp" marking
referred to under this formation.
CARDANUS.--A fine regular ring-plain, about 32 miles in diameter, near
the limb N. of Olbers. Its bright walls, rising about 4000 feet above the
light grey floor, are clearly terraced, and exhibit, especially on the
S.E., several spurs and buttresses. There is a fine valley on the outer
W. slope, a large bright crater on the Mare just beyond its foot, and a
conspicuous mountain in the same position farther north. I have not
succeeded in seeing the faint central hill nor the crater N. of it shown
by Schmidt, but there is a brilliant white circular spot on the floor at
the inner foot of the N.E. wall which he does not show.
KRAFFT.--A very similar object on the N., of about the same dimensions;
with a central peak, and a large crater on the dark floor abutting on the
S.W. wall, and another of about half the size on the outer side of the W.
border. From this crater a very remarkable cleft runs to the N. wall of
Cardanus: it is bordered on either side by a bright bank, and cuts
through the N.W. border of the latter formation. It is best seen when the
E. wall of Cardanus is on the morning terminator.
VASCO DE GAMA.--A bright enclosure, 51 miles in diameter, with a small
central mountain. It is associated on the N. with a number of enclosed
areas of a similar class, all too near the limb to be well seen.
SELEUCUS.--A considerable ring-plain, 32 miles in diameter, with lofty
terraced walls, rising 10,000 feet above a dark floor which includes an
inconspicuous central hill. This formation stands on a ridge extending
from near Briggs to the W. side of Cardanus.
OTTO STRUVE.--An enormous enclosure, bounded on the E. by the Hercynian
Mountains, and on the W. by a mountain chain of considerable altitude,
surmounted by three or more bright little rings. On the W. side of the
uneven-toned interior, which, according to Madler, includes an area of
more than 26,000 square miles, stand four craters, several little hills,
and light spots. On the W. is the much more regular and almost as large
formation, Otto Struve A, the W. border of Otto Struve forming its E.
wall. This enclosure is bounded elsewhere by a very low, broken, and
attenuated barrier. At sunrise the E. and W. walls, with the mountain
mass at the N. end, which they join, resemble a pair of partially-opened
calipers. There is one conspicuous little crater on the W. side of the
floor; and, at or near full moon, four or five white spots, nearly
central, are prominently visible.
BRIGGS.--This bright regular ring-plain, 33 miles in diameter, is
situated a short distance N. of Otto Struve A. A long ridge traverses the
interior from N. to S. On the E. is another large enclosure,
communicating with Otto Struve on the S., and really forming a N.
extension of this formation. It has a large and very deep crater, 12
miles in diameter, on its W. border.
LICHTENBERG.--A conspicuous little ring-plain, about 12 miles in
diameter, in an isolated position on the Mare, some distance N. of
Briggs. It was here that Madler records having occasionally noticed a
pale reddish tint, which, though often searched for, has not been
subsequently seen.
ULUGH BEIGH.--A good-sized ring-plain, E. of the last, with a bright
border and central mountain. Too near the limb for observation.
LAVOISIER.--A small bright walled-plain N. of Ulugh Beigh. It has a
somewhat dark interior. West of it is Lavoisier A, a ring-plain about 14
miles in diameter. Both are too near the limb for useful observation.
GERARD.--A large enclosure close to the limb, still farther N.,
containing a long ridge and a crater.
HARDING.--A small ring-plain W. of Gerard, remarkable for the peculiar
form of its shadow at sunrise, and for the ridges in its vicinity.
REPSOLD.--The largest of a group of walled enclosures, close to the limb,
on the E. side of the Sinus Roris.
XENOPHANES.--But for its position, this deep walled-plain, 185 miles in
diameter, would be a fine telescopic object, with its lofty walls, large
central mountain, and other details.
OENOPIDES.--A large and tolerably regular walled-plain, 43 miles in
diameter, on the W. of the last. The depressions on the W. wall are worth
examination at sunrise. There is apparently no detail whatever on the
floor.
CLEOSTRATUS.--A small ring-plain, N. of Xenophanes, surrounded by a
number of similar objects, all too near the limb for observation.
PYTHAGORAS.--A noble walled-plain, 95 miles in diameter, which no one who
observes it fails to lament is not nearer the centre of the disc, as it
would then undoubtedly rank among the most imposing objects of its class.
Even under all the disadvantages of position, it is by far the most
striking formation in the neighbourhood. Its rampart rises, at one point
on the N., to a height of nearly 17,000 feet above the floor, on which
stands a magnificent central mountain, familiar to most observers.
THIRD QUADRANT
EAST LONGITUDE 0 deg. TO 20 deg.
MOSTING.--A very deep ring-plain, 15 miles in diameter, near the moon's
equator, and about 6 deg. E. of the first meridian. There is a crater on
the N. side of its otherwise unbroken bright border, an inconspicuous
central mountain, and, according to Neison, a dark spot on the S. side of
the floor. At some distance on the S.S.W., stands the bright crater,
Mosting A, one of the most brilliant objects on the moon's visible
surface.
REAUMUR.--A large pentagonal enclosure, about 30 miles in diameter, with
a greatly broken border, exhibiting many wide gaps, situated on the E.
side of the Sinus Medii, N.W. of Herschel. The walls are loftiest on the
S. and S.W., where several small craters are associated with them. A
ridge connects the formation with the great deep crater Reaumur A, and a
second large enclosure lying on the W. side of the well-known valley W.
of Herschel. At the end of a spur on the S. side of the great crater
originates a cleft, which I have often traced to the N.W. wall of
Ptolemaeus, and across the N. side of the floor of this formation to a
crater on the N.E. quarter of it, Ptolemaeus _d_. There is a short cleft
on the W. side of the floor of Reaumur, running from N. to S.
HERSCHEL.--A typical ring-plain, situated just outside the N. border of
Ptolemaeus, with a lofty wall rising nearly 10,000 feet above a somewhat
dusky floor, which includes a prominent central mountain. Its bright
border is clearly terraced both within and without, the terraces on the
inner slope of the W. wall being beautifully distinct even under a high
light, and on the outer slope are some curious irregular depressions. On
the S.S.E. is a large oblong deep crater, close to the rocky margin of
Ptolemaeus, and a little beyond the foot of the wall on the N.W. is a
smaller and more regular rimmed depression, _b_, standing near the E.
border of the great valley, more than 80 miles long, and in places fully
10 miles wide, which runs from S.S.W. to N.N.E. on the W. side of
Herschel, and bears a close resemblance to the well-known Ukert Valley.
Herschel _d_ is a large but shallow ring-plain on the E. of Herschel,
with a brilliant but smaller crater on the W. of it.
North of Herschel, on a plateau concentric with its outline, stands the
large polygonal ring-plain Herschel _a_, a formation of a very
interesting character, with a low broken wall, exhibiting many gaps, and
including some craters of a minute class. The largest of these stands on
the S.W. wall. Mr. W.H. Maw has detected some of these objects on the N.
side, both in connection with the border and beyond it.
FLAMMARION.--A large incomplete walled-plain N.E. of Herschel, open
towards the N., with a border rising about 3000 feet above the floor. The
brilliant crater, Mosting A, stands just outside the wall on the E.
PTOLEMAEUS.--Taking its very favourable position into account, this is
undoubtedly the most perfect example of a walled-plain on the moon's
visible superficies. It is the largest and most northerly component of
the fine linear chain of great enclosures, which extend southwards, in a
nearly unbroken line, to Walter. It exhibits a very marked departure from
circularity, the outline of the border approximating in form to a hexagon
with nearly straight sides. It includes an area of about 9000 square
miles, the greatest distance from side to side being about 115 miles. It
is, in fact, about equal in size to the counties of York, Lancashire, and
Westmorland combined; and were it possible for one to stand near the
centre of its vast floor, he might easily suppose that he was stationed
on a boundless plain; for, except towards the west, not a peak, or other
indication of the existence of the massive rampart would be discernible;
and even in this direction he would only see the upper portion of a great
mountain on the wall.
The border is much broken by gaps and intersected by passes, especially
E. and S., where there are several valleys connecting the interior with
that of Alphonsus. The loftiest portion of the wall, which includes many
crateriform depressions, is on the W., where one peak rises to nearly
9000 feet. Another on the N.E. is about 6000 feet above the interior. On
the N.W. is a remarkable crater-row, called, from its discoverer, "Webb's
furrow," running from a point a little N. of a depression on the border
to a larger crateriform depression on the S. of Hipparchus K. Birt terms
it "a very fugitive and delicate lunar feature." As regards the vast
superficies enclosed by this irregular border, it is chiefly remarkable
for the number of large saucer-shaped hollows which are revealed on its
surface under a low sun. They are mostly found on the eastern quarter of
the floor. Some of them appear to have very slight rims, and in two or
three instances small craters may be detected within them. Owing to their
shallowness, they are very evanescent, and can only be glimpsed for an
hour or so about sunrise or sunset. The large bright crater A, about 4
miles in diameter on the N.W. side of the interior, is by far the most
conspicuous object upon it. Adjoining it on the N. is a large ring with a
low border, and N. of this again is another, extending to the wall. Mr.
Maw and Mr. Mee have seen minute craters on the borders of these obscure
formations. In addition to the objects just specified, there is a fairly
conspicuous crater, _d_, on the N.E. quarter of the floor, and a very
large number of others distributed on its surface, which is also
traversed by a network of light streaks, that have recently been
carefully recorded by Mr. A.S. Williams. A cleft, from near Reaumur A,
traverses the N. side of the floor, and runs up to Ptolemaeus _d_.
ALPHONSUS.--A large walled-plain, 83 miles in diameter, with a massive
irregular border abutting on the S.S.E. side of Ptolemaeus, and rising at
one place on the N.W. to a height of 7000 feet above the interior. The
floor presents many features of interest. It includes a bright central
peak, forming part of a longitudinal ridge, on either side of which runs
a winding cleft, originating at a crater-row on the N. side of the
interior. There is a third cleft on the N.W. side, and a fourth near the
foot of the E. wall. There are also three peculiar dark areas within the
circumvallation; two, some distance apart, abutting on the W. wall, and a
third, triangular in shape, at the foot of the E. wall. The last-
mentioned cleft traverses this patch. These dusky spots are easily
recognised in good photographs of the moon.
ALPETRAGIUS.--A fine object, 27 miles in diameter, closely connected with
the S.E. side of Alphonsus. It has peaks on the W. towering 12,000 feet
above the floor, on which there is an immense central mountain, which in
extent, complexity, and altitude surpasses many terrestrial mountain
systems--as, for example, the Snowdonian group. The massive barrier
between Alpetragius and Alphonsus deserves careful scrutiny, and should
be examined under a moderately low morning sun. On the E., towards
Lassell, stands a brilliant light-surrounded crater.
ARZACHEL.--Another magnificent object, associated on the N. with
Alphonsus, about 66 miles in diameter, and encircled by a massive complex
rampart, rising at one point more than 13,000 feet above a depressed
floor. It presents some very suggestive examples of terraces and large
depressions, the latter especially well seen on the S.E. The bright
interior includes a large central mountain with a digitated base on the
S.E., some smaller hills on the S. of it, a deep crater W. of it (with
small craters N. and S.), and, between the crater and the foot of the W.
wall, a very curious winding cleft.
LASSELL.--This ring-plain, some 14 miles in diameter, is irregular both
as regards its outline and the width of its rampart. There is a crater on
the crest of the N.W. wall, just above a notable break in its continuity
through which a ridge from the N.W. passes. There is another crater on
the opposite side. The central mountain is small and difficult to see.
About 20 miles N.E. of Lassell is a remarkable mountain group associated
with a bright crater, and further on in the same direction is a light
oval area, about 10 miles across, with a crater (Alpetragius _d_) on its
S. edge. Madler described this area as a bright crater, 5 miles in
diameter, which now it certainly is not.
LALANDE.--A very deep ring-plain, about 14 miles in diameter, N.E. of
Ptolemaeus, with bright terraced walls, some 6000 feet above the floor,
which contains a low central mountain. On the N. is the long cleft
running, with some interruptions, in a W.N.W. direction towards Reaumur.
DAVY.--A deep irregular ring-plain, 23 miles across, on the Mare E. of
Alphonsus. There is a deep crater with a bright rim on its S.W. wall, and
E. of this a notable gap. There is also a wide opening on the N. The E.
wall is of the linear type. A cleft crosses the interior.
GUERIKE.--The most southerly member of a remarkable group of partially
destroyed walled-plains, standing in an isolated position in the Mare
Nubium. Its border, on the W. and N. especially, is much broken, and
never rises much more than 2000 feet above the Mare, except at one place
on the N., where there is a mountain about 1000 feet higher. The E. wall
is tolerably continuous, but is of a very abnormal shape. On the S. there
is a peculiar LAMBDA-shaped gap (with a bright crater, and another less
prominent on the E. side of it), the narrowest part of which opens into a
long wide winding valley, bounded by low hills, extending to the W. side
of a bright ring-plain, Guerike B, on the S.E. A crater-chain occupies
the centre of this valley. There is much detail within Guerike. A large
deep bright crater stands under the E. border on a mound, which,
gradually narrowing in width, extends to the N. wall; and a rill-like
valley runs from the N. border towards the E. side of the LAMBDA-shaped
gap. In addition to these features, there is a shallow rimmed crater,
about midway between the extremities of the rill-valley, and several
minor elevations on the floor.
On the broken N. flank of Guerike is a number of incomplete little rings,
all open to the N.; and E. of these commences a linear group of lofty
isolated mountain masses extending towards the W. side of Parry, and
prolonged for 30 miles or more towards the north. They are arranged in
parallel rows, and remind one of a Druidical avenue of gigantic monoliths
viewed from above. They terminate on the S. side of a large bright
incomplete ring (with a lofty W. wall), connected with the W. side of
Parry.
PARRY.--A more complete formation than Guerike. It is about 25 miles in
diameter, and is encompassed by a bright border, which, at a point on the
E., is nearly 5000 feet in height. It is intersected on the N. by passes
communicating with the interior of Fra Mauro. There is a crater, nearly
central, on the dusky interior, which, under a low sun, when the shadows
of the serrated crest of the W. wall reach about half-way across the
floor, appears to be the centre of three or four concentric ridges, which
at this phase are traceable on the E. side of it. There is a conspicuous
crater on the E. wall, below which originates a distinct cleft. This
object skirts the inner foot of the E. border, and after traversing the
N. wall, strikes across the wide expanse of Fra Mauro, and is ultimately
lost in the region N. of this formation. Parry A, S. of Parry, is a very
deep brilliant crater with a central hill and surrounded by a glistening
halo. A cleft, originating at a mountain arm connected with the E. side
of Guerike, runs to the S. flank of this object, and is probably
connected with that which skirts the floor of Parry on the E.
BONPLAND.--A ruined walled-plain with a low and much broken wall, which
on the S.W. appears to be an attenuated prolongation of that of Parry. It
is of the linear type, the formation approximating in shape to that of a
pentagon. The floor is crossed from N. to S. by a fine cleft which
originates at a crater beyond the S. wall, and is visible as a light
streak under a high light. Schmidt shows a short cleft on the W. of this.
FRA MAURO.--A large enclosure of irregular shape, at least 50 miles from
side to side, abutting on Parry and Bonpland. In addition to the cleft
which crosses it, the floor is traversed by a great number of ridges, and
includes at least seven craters.
THEBIT.--A fine ring-plain, 32 miles in diameter, on the mountainous W.
margin of the Mare Nubium, N.E. of Purbach. Its irregular rampart is
prominently terraced, and its continuity on the N.E. interrupted by a
large deep crater (Thebit A), at least 9 miles in diameter, which has in
its turn a smaller crater, of about half this size, on its margin, and a
small central mountain within, which was once considered a good optical
test, though it is not a difficult object in a 4 inch achromatic, if it
is looked for at a favourable phase. The border of Thebit rises at one
place on the N.W. to a height of nearly 10,000 feet above the interior,
which includes much detail. The E. wall of Thebit A attains the same
height above its floor, which is depressed more than 5000 feet below the
Mare.
BIRT.--This ring-plain, about 12 miles in diameter, is situated on the
Mare Nubium, some distance due E. of Thebit. It has a brilliant border,
surmounted by peaks rising more than 2000 feet above the Mare, and a very
depressed floor, which does not appear to contain any visible detail. A
bright crater adjoins it on the S.W., the wall of which at the point of
junction is clearly very low, so that under oblique light the two
interiors appear to communicate by a narrow pass or neck filled with
shadow. I have frequently seen a break in the N.W. wall of Birt, which
seems to indicate the presence of a crater. There is a noteworthy cleft
on the E., which can be traced from the foot of the E. wall to the hills
on the N.E. It is a fine telescopic object, and, under some conditions,
the wider portion of it resembles a railway cutting traversing rising
ground, seen from above. It is visible as a white line under a high
light.
THE STRAIGHT WALL.--Sometimes called "the railroad," is a remarkable and
almost unique formation on the W. side of Birt, extending for about 65
miles from N.E. to S.W. in a nearly straight line, terminating on the
south at a very peculiar mountain group, the shape of which has been
compared to a stag's horn, but which perhaps more closely resembles a
sword-handle,--the wall representing the blade. When examined under
suitable conditions, the latter is seen to be slightly curved, the S.
half bending to the west, and the remainder the opposite way. The
formation is not a ridge, but is clearly due to a sudden change in the
level of the surface, and thus has the outward characteristics of a
"fault" Along the upper edge of this gigantic cliff (which, though
measures differ, cannot be anywhere much less than 500 feet high) I have
seen at different times many small craterlets and mounds. Near its N. end
is a large crater, and on the W. is a row of hillocks, running at right
angles to the cliff. No observer should fail to examine the wall under a
setting sun when the nearly perpendicular E. face of the cliff is
brilliantly illuminated.
NICOLLET.--A conspicuous little ring-plain on the E. of Birt, and
somewhat smaller. Between the two is a still smaller crater, from near
which runs a low mountain range, nearly parallel to the straight wall, to
the region S.E. of the Stag's Horn Mountains. Here will be found three
small light-surrounded craters arranged in a triangle, with a somewhat
larger crater in the middle.
PURBACH.--An immense enclosure of irregular shape, approximating to that
of a rhomboid with slightly curved sides. It is fully 60 miles across,
and the walls in places exceed 8000 feet in altitude, and include many
depressions, large and small. On the E. inner slope are some fine
terraces and several craters. The continuity of the circumvallation is
broken on the N. by a great ring-plain, on the floor of which I have seen
a prominent cleft and a crater near the S. side. There is a large bright
crater in the interior of Purbach, S. of the centre, two others on the W.
half of the floor, and a few ridges.
REGIOMONTANUS.--A still more irregular walled-plain, of about the same
area, closely associated with the S. flank of Purbach, having a rampart
of a similar complex type, traversed by passes, longitudinal valleys, and
other depressions. Schmidt alone shows the especially fine example of a
crater-row, which is not a difficult object, in connection with the S.E.
wall. Excepting one crater, nearly central, and some inconspicuous
ridges, I have seen no detail on the floor. Schmidt, however, records
many features.
WALTER.--A great rhomboidal walled-plain, 100 miles in diameter, with a
considerably depressed floor, enclosed by a rampart of a very complex
kind, crowned by numerous peaks, one of which, on the W., rises 10,000
feet above the interior. If the formation is observed when it is close to
the morning terminator, say, when the latter lies from l deg. to 2 deg.
E. of the centre of the floor, it is one of the most striking and
beautiful objects which the lunar observer can scrutinize. The inner
slope of the border which abuts on Regiomontanus, examined at this phase
under a high power, is seen to be pitted with an inconceivable number of
minute craters; and the summit ridge, and the region towards Werner,
scalloped in a very extraordinary way, the engrailing (to use an heraldic
term) being due to the presence of a row of big depressions. The floor at
this phase is sufficiently illuminated to disclose some of its most
noteworthy features. Taking its area to be about 8000 square miles, at
least 1200 square miles of it is occupied by the central mountain group
and its adjuncts, the highest peak rising to a height of nearly 5000 feet
(or nearly 600 feet higher than Ben Nevis), above the interior, and
throwing a fine spire of shadow thereon. In the midst of this central
boss are two deep craters, one being about 10 miles in diameter, and a
number of shallower depressions. In association with the loftiest peak, I
noted at 8 h., March 9, 1889, two brilliant little craters, which
presumably are not far from the summit. Near the E. corner of the floor
there is another large deep crater, and, ranging in a line from the
centre to the S.E. wall, three smaller craters.
LEXELL.--On the E. of Walter extends an immense plain of irregular
outline, which is at least equal to it in area. Though no large formation
is found thereon; many ridges, short crater-rows, and ordinary craters
figure on its rugged superficies; and on its borders stand some very
noteworthy objects, among them, on the S., the walled-plain Lexell, about
32 miles in diameter, which presents many points of interest. Its
irregular wall, rising, at one point on the S.W., to a height of nearly
8000 feet, is on the N.W. almost completely wanting, only very faint
indications of its site being traceable, even under a low morning sun. On
the opposite side it is boldly terraced, and has a large crater on its
summit. The interior, the tone of which is conspicuously darker than that
of the region outside, contains a small central hill, with two craters
connected with it. The low N.W. margin is traversed by a delicate valley,
which, originating on the N. side of the great plain, crosses the W.
quarter of Lexell and terminates apparently on the S.W. side of the
floor.
HELL.--A prominent ring-plain, about 18 miles in diameter, on the E. side
of the great plain. There is a central mountain and many ridges within.
BALL.--A somewhat smaller ring-plain on the S.E. edge of the great plain,
with a lofty terraced border and a central mountain more than 2000 feet
high. There are two large irregular depressions on the W. of the
formation, a crater on the S., and a smaller one on the N. wall.
PITATUS.--This remarkable object, 58 miles in diameter, with Hesiodus,
its companion on the E., situated at the extreme S. end of the Mare
Nubium, afford good examples of a class of formations which exhibit
undoubted signs of partial destruction, from some unknown cause, on that
side of them which faces the Mare. On every side but the N., Pitatus is a
walled plain of an especially massive type, the border on the S.E.
furnishing one of the finest examples of terraces to be found on the
visible surface. On the S.W., two parallel rows of large crateriform
depressions, perhaps the most remarkable of their kind, extend for 60
miles or more to the W. flank of Gauricus. On the N.W., the rampart
includes many curious irregular depressions and craters, and gradually
diminishes in height, till, for a space of about 12 miles on the N.,
there can hardly be said to be any border at all, its site being marked
by some inconsiderable mounds and shallow hollows. There is a small
bright central mountain on the floor, and, S. of it, two larger but lower
elevations. A distinct straight cleft traverses the N.W. side of the
interior very near the wall, to which it forms an apparent chord, and a
second cleft occupies a similar position with respect to the bright N.E.
border. A narrow pass forms a communication with the interior of
Hesiodus.
HESIODUS.--This walled-plain, little more than half the diameter of the
last, has an irregular outline, and for the most part linear walls, which
on the S. are massive and lofty (4000 feet), but on the N. very low, and
broken by gaps. There is a fine deep crater on the S. border, and a small
but distinct crater on the floor, nearly central, the only object thereon
which I have seen, though Schmidt draws a smaller one on the W. of it.
A mountain abutting on the N.E. side of Hesiodus is the W. origin of one
of the longest clefts on the moon. Running in an E.S.E. direction, it
traverses the Mare to a crater near the W. face of the Cichus mountain
arm, reappears on the E. side of this object, and is finally lost amid
the hills on the N. of Capuanus. The W. section of this cleft is coarser
and much more distinct than that lying E. of the mountain arm.
GAURICUS.--A large walled-plain S. of Pitatus, about 40 miles in
diameter. The border is very irregular, and, according to Neison,
consists on the E. of a precipitous cliff more than 9000 feet high. It is
surrounded by a number of large rings on the S., and has several
considerable small depressions on its N. border. There is apparently no
prominent detail on the floor. Schmidt shows some ridges and craterlets.
WURZELBAUER.--Another irregular walled-plain, about 50 miles in diameter,
on the S.E. of Pitatus, with a very complex border, in connection with
which, on the S.W., is a group of fine depressions, and on the S.E. a
large crater. There is much detail on the very uneven floor.
MILLER.--One of a group of three moderately large ring-plains, of which
Nasireddin is a member, near the central meridian in S. latitude 39 deg.
Its massive border rises nearly 11,000 feet above the floor, on which
stands a central peak. Miller is about 36 miles in diameter.
NASIREDDIN.--A somewhat smaller ring-plain on the S. of the last, and of
a very similar type. It contains a central peak and several minor
elevations. Between its N.W. border and the S.W. flank of Miller is a
smaller ring-plain of about half the size of Nasireddin, and on the S.E.
a large enclosure named HUGGINS.
ORONTIUS.--Huggins has encroached on the W. side of this irregular ring-
plain and overlaps it. It is of considerable size. The floor includes
much detail and a prominent crater.
SASSERIDES.--A formation of irregular shape, with very lofty walls,
situated amid the confusion of ring-plains, craters, crater-pits, &c., in
the region N. of Tycho, some of which are fully as deserving of a
distinct name.
HEINSIUS.--A very curious formation on the N.E. of Tycho: a fine
telescopic object under oblique illumination. It has an irregular but
continuous border, except on the S., where two large ring-plains have
encroached upon it, and a third, N. of a line joining their centres,
occupies no inconsiderable portion of the floor. Heinsius is nearly 50
miles across, and the border on the W., is nearly 9000 feet above the
interior, which includes, at least, three small craters. The walls of the
intrusive ring-plains have craters on their summits; the more westerly
has two on the W., and its companion, one on the S.W. The ring-plain on
the floor has a crater on its E. wall. Schmidt shows a small crater
between the ring-plains on the S. border.
SAUSSURE.--A ring-plain W. of Tycho, 28 miles in diameter, with bright
lofty terraced walls and a somewhat dark interior, on which there is a
crater, W. of the centre, and some crater-pits. There are several large
depressions on the S.W. wall. It is surrounded by formations which,
though nearly as prominent as itself, have not, with the exception of
Pictet on the E., and one on the N.W., called Huggins by Schmidt,
received distinctive names. The region W. of Saussure abounds in
craterlets, some of which are of the minutest type. One of the Tycho
streaks is manifestly deflected from its course by this formation, and
another is faintly traceable on the floor.
PICTET.--A walled-plain of irregular shape, about 30 miles across,
between Saussure and Tycho, with a border broken on the S. by a large
conspicuous ring-plain, which is at least 10 miles in diameter, and,
according to Schmidt, has a central mountain. Schmidt draws the S.E.
border of Pictet as broken by ridges extending on to the floor. He also
shows several craters and minor elevations thereon.
TYCHO.--As the centre from which the principal bright ray-system of the
moon radiates, and the most conspicuous object in the southern
hemisphere, this noble ring-plain may justly claim the pre-eminent title
of "the Metropolitan crater." It is more than 54 miles in diameter, and
its massive border, everywhere traversed by terraces and variegated by
depressions within and without, is surmounted by peaks rising both on the
E. and W. to a height of about 17,000 feet above the bright interior, on
which stands a magnificent central mountain at least 5000 feet in
altitude. Were it not somewhat foreshortened, Tycho would be seen to
deviate considerably from what is deemed to be the normal shape. On the
S. and W. especially, the wall approximates to the linear type, no signs
of curvature being apparent where these sections meet. The crest on the
S. and S.E. exhibits many breaks and irregularities; and it is through a
narrow gap on the S. that a rill-like valley, originating at a small
depression near the foot of the S.W. _glacis_, passes, and, descending
the inner slope of the S.E. wall obliquely, terminates near its foot.
There is a distinct crater on the summit ridge on the S.E., and another
below the crest on the outer S.W. slope. On the S. inner slope I have
often remarked a number of bright oval objects, which, for the lack of a
better word, may be termed "mounds" though they represent masses of
material many miles in length and breadth. The outer slope of Tycho,
exhibiting under a high light a grey nimbus encircling the wall,
includes--craters, crater-pits, shallow valleys, spurs and buttresses--in
short, almost every variety of lunar feature is represented. Excepting
the central mountain and a crater on the W. of it, I have not seen any
object on the floor, which, for some unexplained reason, is never very
distinct. Schmidt shows several low ridges on the N.E. side. In a paper
recently published in the _Astronomische Nachrichten_, Professor W.H.
Pickering, describing his observations of the Tycho streaks made at
Arequipa, Peru, with a 13 inch achromatic, asserts that they do not
radiate from the centre of Tycho, but from a multitude of minute craters
on its S.E. or N. rim. (See Introduction.)
MAGINUS.--An immense partially ruined enclosure, at least 100 miles from
side to side, on the S.W. of Tycho, from which it is separated by a
region covered with a confused mass of ring-plains and craters. On almost
every part of its broken border stand large ring-plains, many of which,
if they were isolated, or situated in a less disturbed region, would rank
as objects of importance; but among such a multitude of features they
pass unnoticed. The largest of them occupies no inconsiderable part of
the S.E. wall, and is quite 30 miles in diameter, its own border being
also much broken by depressions, as, indeed, are those of almost all the
six or more large ring-plains which define the N. limits of Maginus. The
loftiest portion of what remains of a true border rises at one place to
more than 14,000 feet. On the floor, which is traversed by some of the
Tycho rays, there is a mountain group associated with a crater, nearly
central, and several large rings on the N. side. Though the formation is
very difficult to detect under a high sun, Madler's dictum that "the full
moon knows no Maginus" is not strictly true.
STREET.--A walled-plain between Tycho and Maginus, about 28 miles in
diameter, with a border of moderate height, broken by depressions on the
N. There are some small craters and ridges within; but the surrounding
region, with its almost endless variety of abnormally shaped formations,
is far more worthy of the observer's attention.
DELUC.--The largest and most prominent member of a curious group of ring-
plains on the S.W. of Maginus. It is about 28 miles in diameter, and is
encircled by a wall some 7000 feet above the interior, which includes a
crater. A large ring with a central mountain encroaches on the N. wall,
and a smaller object of the same class on the S. wall.
CLAVIUS.--There are few lunar observers who have not devoted more or less
attention to this beautiful formation, one of the most striking of
telescopic objects. However familiar we may consider ourselves to be with
its features, there is always something fresh to note and to admire as
often as we examine its apparently inexhaustible details. It is 142 miles
from side to side, and includes an area of at least 16,000 square miles
within its irregular circumvallation, which is only comparatively
slightly elevated above the bright plateau on the W., though it stands at
least 12,000 feet above the depressed floor. At a point on the S.W. a
peak rises nearly 17,000 feet above the interior, while on the E. the
cliffs are almost as lofty. There are two remarkable ring-plains, each
about 25 miles in diameter, associated, one with the N., and the other
with the S. wall, the floors of both abounding in detail. The latter,
however, is the most noteworthy on account of the curious corrugations
visible soon after sunrise on the outer N. slope of its wall, resembling
the ribbed flanks of some of the Java volcanoes. There are five large
craters on the floor of Clavius, following a curve convex to the N., and
diminishing in size from W. to E. The most westerly stands nearly midway
between the two large ring-plains on the walls, the second (about two-
thirds its area) is associated with a complex group of hills and smaller
craters. Both these objects have central mountains. In addition to this
prominent chain, there are innumerable craters of a smaller type on the
floor, but they are more plentiful on the S. half than elsewhere. On the
S.E. wall are three very large depressions. On the broad massive N.E.
border, the bright summit ridge and the many transverse valleys running
down from it to the floor, are especially interesting features. There are
very clear indications of "faulting" on a vast scale where this broad
section of the wall abuts on the N. side of the formation.
CYSATUS.--A regular walled-plain, apparently about 28 miles in diameter,
forming the most northerly member of a chain of formations, of which
Newton, Short, and Moretus, extending towards the S. limb, form a part.
Its border rises nearly 13,000 feet above a floor devoid of prominent
detail.
GRUEMBERGER.--A much larger and more irregular ring-plain, nearly 40
miles from wall to wall, on the E. side of Cysatus. Its W. border rises
nearly 14,000 feet above the interior, which includes an abnormally deep
crater, the bottom of which is 20,000 feet below the crest of the W.
wall, and several small depressions and ridges. The inner E. slope is
finely terraced.
MORETUS.--A magnificent object, 78 miles in diameter, but foreshortened
into a flat ellipse. Its beautifully terraced walls and magnificent
central mountain, nearly 7000 feet high, are very conspicuous under
suitable conditions. The rampart on the E. is more than 15,000 feet above
the floor, while on the opposite side it is about 5000 feet lower.
SHORT.--A fine but foreshortened ring-plain of oblong shape, squeezed in
between Moretus and Newton. It is about 30 miles in diameter, and on the
S.E., where its border and that of Newton are in common, it rises nearly
17,000 feet above the interior, which includes, according to Neison, a
small central hill. Schmidt shows a crater on the N. side of the floor.
NEWTON.--Is situated on the S.E. side of Short, and is the deepest
walled-plain on the visible surface. It is of irregular form and about
143 miles in extreme length. One gigantic peak on the E. rises to nearly
24,000 feet above the floor, the greater part of which is always immersed
in shadow, so that neither the earth or sun can at any time be seen from
it.
MALAPERT.--A ring-plain situated far too near the limb for useful
observation. Between it and Newton is a number of abnormally shaped
enclosures.
CABEUS.--Another object out of the range of satisfactory scrutiny. Madler
considered that it is as deep as Newton. According to Neison, a central
peak and two craters can be seen within under favourable conditions.
Schmidt draws a long row of great depressions on the N. side of it.
EAST LONGITUDE 20 deg. TO 40 deg.
LANDSBERG.--A ring-plain, about 28 miles in diameter, situated in Mare
Nubium, S.E. of Reinhold, which in many respects it resembles. Its
regular massive border is everywhere continuous. Only a solitary crater
breaks the uniformity of its crest, that rises on the W. to nearly 10,000
feet, and on the E. to about 7000 feet above the floor, which is
depressed about 7000 feet below the surrounding surface. The inner slopes
exhibit some fine terraces, and on the broad W. _glacis_ is a curious
winding valley, which runs up the slope from the S.W. side to the crater
just mentioned, then, bending downwards, joins the plain at the foot of
the N. wall. Neither this nor the crater is shown in the maps. The large
compound central peak is apparently the sole object in the interior. At 8
h. 25 m. on January 23, 1888, when observing the progress of sunrise on
this formation with a 8 1/2 inch Calver-reflector charged with different
eyepieces, I noticed, when about three-fourths of the floor was in
shadow, that the illuminated portion of it was of a dark chocolate hue,
strongly contrasting with the grey tone of the surrounding district. This
appearance lasted till the interior was more than half illuminated,
gradually becoming less pronounced as the sun rose higher on the ring. E.
and S.E. of Landsberg is a number of ring-plains and craters well worthy
of careful examination. Five of the largest are surrounded by a
glistening halo, and one (that nearest to the formation) and another (the
largest of the group) have each a minute crater on their N. wall.
EUCLIDES.--One of the most brilliant objects on the moon; a crater 7
miles in diameter, standing on a large bright area in the Mare
Procellarum, E. of the Riphaean Mountains. Its E. rim rises nearly 2000
feet above the bright depressed floor; on the W. there is a bright little
unrecorded crater.
WICHMANN.--This bright crater, about 5 miles in diameter, stands on a
light area in Oceanus Procellarum, N.N.W. of Letronne and nearly due E.
of Euclides. Some distance on the N.E. are the relics of what appears
once to have been a large enclosure, represented now by a few isolated
mountains.
HERIGONIUS.--A ring-plain, about 7 miles in diameter, in the Mare
Procellarum, N.W. of Gassendi. There is a small crater a few miles S.E.
of it, among the bright little mountains which flank this formation.
Herigonius has a small central mountain, which is a good test for
moderate apertures.
GASSENDI.--One of the most beautiful telescopic objects on the moon's
visible surface, and structurally one of the most interesting and
suggestive. It is a walled-plain, 55 miles in diameter, of a distinctly
polygonal type, the N.W. and S.W. sections being practically straight,
while the intermediate W. section exhibits a slightly convex curvature,
or bulging in towards the interior. There is also much angularity about
the E. side, which is evident at an early stage of sunrise. The wall on
the N. is broken through and almost completely wrecked by the great ring-
plain Gassendi A. The bright eastern section of the border is in places
very lofty, rising at one peak, N. of the well-known triangular
depression upon it, to 9000 feet, and at other peaks on the same side
still higher. It is very low on the S., being only about 500 feet above
the surface. The floor, however, on the N. stands 2000 feet above the
Mare Humorum. On the W. there is a peak towering 4000 feet above the
wall, which is here about 5000 feet above the floor, and 8000 feet above
the Mare Nubium. A very notable feature in connection with this formation
is the little bright plain bounding it on the N.W., and separated from it
by merely a narrow strip of wall. This enclosure is flanked on the N.E.
by Gassendi A, and on the S.W. and N.W. by a coarse winding ridge,
running from the W. wall and terminating at a large irregular dusky
depression. Gaudibert has detected a crater near the S.E. edge of this
bright plain, which includes also some oval mounds. The interior of
Gassendi is without question unrivalled for the variety of its details,
and, after Plato, has perhaps received more attention from observers than
any other object. The bright central mountain, or rather mountains, for
it consists of a number of grouped masses crowned by peaks, of which the
loftiest is about 4000 feet, is one of the finest on the moon. It was
carefully studied with a 6 1/4 inch Cooke-achromatic by the late
Professor Phillips, the geologist, who compared it to the dolomitic or
trachytic mountains of the earth. The buttresses and spurs which it
throws out give its base a digitated outline, easily seen under suitable
illumination. There are between 30 and 40 clefts in the interior, the
majority being confined to the S.W. quarter of the floor. Those most
easily seen pertain to the group which radiates from the central mountain
towards the S.W. wall. They are all more or less difficult objects,
requiring exceptionally favourable weather and high powers. A fine
mountain range, the Percy Mountains, is connected with the E. flank of
Gassendi, extending in a S.E. direction towards Mersenius, and defining
the N.E. side of the Mare Humorum.
BULLIALDUS.--A noble object, 38 miles in diameter, forming with its
surroundings by far the most notable formation on the surface of the Mare
Nubium, and one of the most characteristic ring-plains on the moon. It
should be observed about the time when the morning terminator lies on the
W. border of the Mare Humorum, as at this phase the best view is obtained
of the two deep parallel terrace valleys which run round the bright inner
slope of the E. wall, of the crater-row against which they abut on the
S.E., and of the massive W. _glacis_, with its spurs and depressions. The
S. border of Bullialdus has been manifestly modified by the presence of
the great ring-plain A, a deep irregular formation with linear walls,
which is connected with it by a shallow valley. The rampart of Bullialdus
rises about 8000 feet above a concave floor, which sinks some 4000 feet
below the Mare on the E. With the exception of the fine compound central
mountain, 3000 feet high, there are few details in the interior. On the
S., is the fine ring-plain B, connected with the S.E. wall near the
crater-row by a well-marked valley, and nearly due E. of B is another, a
square-shaped enclosure, C, with a very lofty little mountain on the E.
side of it, and a crater on its S. wall. In addition to these features,
there are many ridges and surface inequalities, very prominent under
oblique illumination.
LUBINIEZKY.--A regular enclosure, about 23 miles in diameter, N.E. of
Bullialdus, with a low attenuated border, which is nowhere more than 1000
feet in height. It is tolerably continuous, except on the S., where there
are two or three breaks. Its level dark interior presents no details to
vary its monotony. Close under the N.W. wall is a small crater connected
with it by a ridge, and E. of this a very rugged area, traversed in every
direction by narrow shallow valleys, which are well worth looking at when
close to the morning terminator. A bright spur projects from the N. wall
of Lubiniezky.
KIES.--A somewhat similar formation, S. of Bullialdus, about 25 miles in
diameter, also encircled by a border of insignificant dimensions,
attaining an altitude of 2400 feet at only one point on the S.E., while
elsewhere it is scarcely higher than that of Lubiniezky. It is clearly
polygonal, approximating to the hexagonal type. On the more distinct S.
section a bright spur projects from it. On the N. its continuity is
broken by a distinct little crater. It is traversed by a remarkable white
streak, extending in a S.W. direction from Bullialdus C (where it is very
wide), across the interior, to the more westerly of two craters S.W. of
Mercator. Another streak branches out from it near the centre of the
floor, and runs to the W. wall. The principal streak, so far as the
portion within Kies is concerned, represents a cleft. On the Mare E. of
Kies is a curious circular mound, and farther towards Campanus two
prominent little mountains. On the N.W. is a large obscure ring and a
wide shallow valley bordered by ridges.
AGATHARCHIDES.--A very irregular complex ring-plain, about 28 miles in
diameter, forming part of the N.W. side of the Mare Humorum. It must be
observed under many phases before one can clearly comprehend its
distinctive features. The wall is very deficient on the N., but is
represented in places by bright mountain masses. The formation is flanked
on the E. by a double rampart, which is at one place more than 5000 feet
in height, with a deep intervening valley. The S. wall is traversed by a
number of parallel valleys, all trending towards Hippalus. These are
included in a much wider and longer chasm, which, gradually diminishing
in breadth, extends up to the N. wall of the latter.
HIPPALUS.--A partially ruined walled-plain, about 38 miles in diameter,
on the W. side of the Mare Humorum, S. of Agatharchides. At least one-
third of the border is wanting on the S.E., but under a low sun its site
can be distinguished by a faint marking and the obvious difference in
tone between the dark interior and the lighter-coloured plain. The rest
of the wall is bright and continuous, except at a place on the W., where
what appears to be the segment of a large ring has encroached upon it.
There are two craters in the interior of Hippalus, and a row of parallel
ridges, running obliquely from the S.W. wall up to a cleft which
traverses the floor from N. to S. W. of Hippalus stands a bright crater,
Hippalus A, with an incomplete little ring-plain adjoining it on the
N.W.; and N.E. of it a much larger obscure ring containing two little
hills. The Hippalus rill-system is a very interesting one, and the
greater part of it can, moreover, be easily traced in a good 4 inch
achromatic. It originates in the rugged region E. of Campanus, from which
five nearly parallel curved clefts extend up to the rocky barrier,
connecting the N. side of this formation with the S.W. side of Hippalus.
The most westerly of these furrows is interrupted by a crater on this
wall, but reappears on the N. side of it, and, after making a detour
towards the W. to avoid a little mountain in its path, runs partially
round the E. flank of Hippalus A, and then, continuing its northerly
course, terminates amid the mountains W. of Agatharchides. (A short
parallel cleft runs E. of this from the little mountain to the E. side of
A.) The most easterly member of the system, originating N. of Ramsden,
enters Hippalus at the S. side of the great gap in the border, and, after
traversing the floor at the W. foot of a ridge thereon, also extends
towards the mountains W. of Agatharchides. Between these clefts are three
intermediate furrows, one of which runs N. from the N. side of the
encroaching ring already referred to, on the W. wall of Hippalus.
CAMPANUS.--A ring-plain, 30 miles in diameter, on the rocky barrier,
extending in nearly a straight line from Hippalus to Cichus. Its terraced
walls, which rise on the E. more than 6000 feet above the floor, are
broken on the S. by a narrow valley, and on the E. by a small crater. A
small central mountain is apparently the only object on a very dark
interior.
MERCATOR.--A more irregular ring-plain of about the same area, adjoining
Campanus on the S.W. Its rampart is somewhat lower, and is partially
broken on the N. by two semi-rings, and on the S. by a gap. The E. wall
extends on the S. far beyond the limits of the formation, and terminates
in a brilliant mountain mass 6000 feet in height. There is a bright
crater on the crest of both the E. and W. border. On the plain E. of
Mercator is a remarkable little crater standing on a light area, and,
just under the wall, a dusky pit connected with it by a rill-like
marking. These objects are of a very doubtful nature, and should be
carefully observed. The floor of Mercator is much lighter than that of
Campanus, and appears to be devoid of detail.
CICHUS.--A conspicuous ring-plain, about 20 miles in diameter, with a
prominent deep crater about 6 miles across on its E. rim. It is situated
on a curious boot-shaped plateau, near the S. end of the rocky mountain
barrier associated with the last two formations. Its walls rise about
9000 feet above a sunken floor, on which there is some faint detail, but
apparently nothing deserving the distinction of a central mountain. The
plateau on the N. is cut through by a fine broad valley, which has
obviously interfered with a large crateriform depression on its southern
edge. A cleft runs from a small crater W. of the plateau up to this
valley, and extends beyond to the W. wall of Capuanus. There is also a
delicate cleft crossing the region S. of Cichus to the group of
complicated formations S.W. of Capuanus. As already mentioned, the great
Hesiodus cleft is associated with the Cichus plateau.
CAPUANUS.--A large ring-plain, about 34 miles in diameter, E. of Cichus,
with a border especially remarkable on the E., where it rises more than
8000 feet above the outside country, and includes a large brilliant
shallow crater. It is broken on the N.W. by a small but noteworthy double
crater; and on the S. its continuity is destroyed for many miles by a
number of big circular and sub-circular depressions and prominent deep
valleys, far too numerous and complicated to describe. The level dusky
interior contains only a low mound on the S., but is crossed by some
light streaks running from N. to S.
RAMSDEN.--This ring-plain, 12 miles in diameter, derives its importance
from the remarkable rill-system with which it is so closely associated.
Its border, about 1800 feet on the W. above the outside surface, is
slightly terraced within on the E., where there is an unrecorded bright
crater on the slope. The two principal clefts on the S. originate among
the hills E. of Capuanus. The more easterly begins at a crater on the N.
edge of these objects, and runs N. to the E. side of Ramsden; the other
originates at a larger crater, and proceeds in a N. direction up to a
bright little mountain S.W. of Ramsden; when, swerving to the N.E., it
ends at the W. wall of this formation. This mountain is a centre or node
from which three other more delicate branches radiate. On the N., three
of the shortest clefts pertaining to the system are easily traceable from
neighbouring mountains up to the N. wall, which they apparently partially
cut through. The E. pair have a common origin, but open out as they
approach the border of Ramsden.
VITELLO.--A very peculiar ring-plain, 28 miles in diameter, on the S.
side of the Mare Humorum, remarkable for having another nearly concentric
ring-plain, of considerably less altitude within it, and a large bright
central boss, overlooking the inner wall, 1700 feet in height. The outer
wall is somewhat irregular, and is broken by gaps and valleys on the S.
and N.W. It rises on the E. about 5000 feet above the Mare, but only
about 2000 above the interior, which includes a crater on its N. side,
and some low ridges.
HAINZEL.--This remarkable formation, which is about 55 miles in greatest
length, but is hardly half so broad, derives its abnormal shape from the
partial coalescence of two nearly equal ring-plains, the walls of both
being very lofty,--more than 10,000 feet. It ought to be observed under a
morning sun when the floor is about half illuminated. At this phase the
extension of the broad bright terraced E. border across a portion of the
interior is very apparent, and the true structural character of the
formation clearly revealed. The floor abounds in detail, among which, on
the S., are some large craters and a bright longitudinal ridge. Hainzel
is flanked on the W. and S.W. by a broad plateau, W. of which stand two
ring-plains about 15 miles in diameter, both having prominent central
mountains and bright interiors.
WILHELM I.--A large irregular formation, about 50 miles across, S.E. of
Heinsius, with walls varying very considerably in height, rising more
than 11,000 feet on the E., but only about 7000 feet on the opposite
side. The border is everywhere crowded with depressions, large and small.
Three ring-plains, not less than 6 miles in diameter, stand upon the S.
wall, the most westerly overlapping its shallower neighbour on the E.,
which projects beyond the wall on to the floor. The interior has a very
rugged and uneven surface, upon the N. side of which are two very
distinct craters, and a short crater-row on the W. of them. It is
traversed from W. to E. by three bright streaks from Tycho, two on the N.
being very prominent under a high light.
LONGOMONTANUS.--A much larger walled-plain, S. of the last. It is 90
miles in diameter, with a border much broken by depressions, especially
on the N.E. At one peak on this side it rises to the tremendous altitude
of 13,000 feet above the floor, and at peaks on the W. more than 1000
feet higher. There is a crowd of ring-plains on the N.E. quarter of the
interior, and some hills and craterlets in other parts of it. It is also
crossed by rays from Tycho.
SCHILLER.--A fine lozenge-shaped enclosure, with a continuous but
somewhat irregular border. It is about 112 miles in extreme length, and
rather more than half this in breadth. The loftiest section of the wall
is on the W., where it rises 13,000 feet above a considerably depressed
interior. There is a bright crater on this side and some terraces. On the
broad inner slope of the E. border, the summit ridge of which is
especially well-marked, there is a large shallow depression. The floor
contains scarcely any detail, except some ridges on the N. side and a few
craterlets. The great bright plain E. of Schiller and the region on the
S.E. are especially worthy of scrutiny under a low morning sun.
BAYER.--This object, 29 miles in diameter, with a terraced border rising
on the W. to a height of 8000 feet above the floor, is so closely
associated with Schiller, that it may almost be regarded as forming part
of it. A long lofty mountain arm, apparently connected with the W. wall
of the latter, runs from the E. side of Bayer towards the N.W. There is a
crater on the E. side of the interior.
ROST.--An oblong-shaped ring-plain, 30 miles in diameter, on the S.W. of
Schiller, with moderately high walls, and, according to Neison, a shallow
depression within, nearly central. I have seen a crater shown by Schmidt
on the E. side of the floor. A valley runs from the E. side of Rost to
the S. of Schiller.
WEIGEL.--A not very conspicuous ring-plain on the S. of Schiller, with a
crater on its N.W. rim, and a larger ring adjoining it on the S.E. A
prominent curved mountain arm from the E. wall of Schiller runs towards
the N. side of this formation.
BLANCANUS.--A formation, 50 miles in diameter, on the S.E. side of
Clavius, whose surpassing beauties tend to render the less remarkable
features of this magnificent ring-plain and those of its neighbour
Scheiner less attractive than they otherwise would be. The crest of its
finely terraced wall, which at one peak on the E. rises to 18,000 feet,
is at least 12,000 feet above the interior. Krieger saw twenty craters on
the floor (1894, Sept. 21, 13h.), most of them situated on the S.
quarter.
SCHEINER.--A still larger object, being nearly 70 miles in diameter, with
a prominently terraced wall, fully as lofty as that of Blancanus. There
is a large crater, nearly central, two others on the N.E. side of the
floor, and a fourth at the inner foot of the E. wall. There is also a
shallow ring on the N.E. slope. Schmidt shows, but far too prominently,
two straight ridges crossing each other on the S. side of the central
crater.
CASATUS.--A large walled-plain, about 50 miles in diameter, S.E. of
Blancanus, near the limb, remarkable for having one of the loftiest
ramparts of all known lunar objects; it rises at one peak on the S.W. to
the great height of 22,285 feet above the floor, while there are other
peaks nearly as high on the N. and S. The wall is broken on the E. by a
fine crater. There is also a crater on the N.W. side of the very
depressed floor, together with some craterlets.
KLAPROTH.--Casatus partially overlaps this still larger but less massive
formation on its S.E. flank. The walls of Klaproth are much lower and
very irregular and broken, especially on the W. There are some ridges on
the floor. The neighbouring region is covered with unnamed objects, large
and small.
EAST LONGITUDE 40 deg. TO 60 deg.
FLAMSTEED.--A bright ring-plain, 9 miles in diameter, in a barren region
in the Oceanus Procellarum, N.E. of Wichmann. It has a regular border
(broken at one place on the N. by a gap, which probably represents a
crater), rising to a height of about 1400 feet above the surrounding
plain. A great enclosure, 60 miles in diameter, lies on the N. of
Flamsteed. It is defined by low ridges which exhibit many breaks, though
under a high light the ring is apparently continuous. Within are several
small craters and two considerable hills, nearly central.
HERMANN.--A ring-plain, about 10 miles in diameter, in the Oceanus
Procellarum, W. of Lohrmann. It is associated with a group of long
ridges, running in a meridional direction and roughly parallel to the
coast-line.
LETRONNE.--A magnificent bay or inflexion in the coast-line of the
Oceanus Procellarum, N.N.E. of Gassendi, presenting an opening towards
the N. of nearly 50 miles, and bounded on the S. and S.W. by the lofty
Gassendi highlands. Its border on the W., about 3000 feet high, is
crowned with innumerable small depressions. The interior includes four
bright little mountains, nearly central (three of them forming a
triangle), a bright crater on the W. side, and several minor elevations
and ridges. On the plain N. of the bay, is a large bright crater, from
which a fine curved ridge runs to the central mountains. If Letronne is
observed under oblique illumination, the low mounds and ridges on the
Mare outside impress one with the idea that they represent the remains of
a once complete N. wall.
BILLY.--A ring-plain, 31 miles in diameter, S.E. of Letronne, with a very
dark floor, depressed about 1000 feet below the grey surface on the W.,
and a regular border, rising more than 3000 feet above it. There is a
narrow gap on the S., and indications of a crater on the N.W. rim. Two
small craters stand on the S. half of the interior. The formation is
flanked on the S.W. by highlands.
HANSTEEN.--A somewhat larger ring-plain, with a lower and more
irregular rampart, rising on the W. to nearly 3000 feet above the
floor, which is depressed to about the same extent as that of Billy.
Both the inner and outer slopes are terraced on the E., where the
_glacis_ is traversed by a short, delicate, rill-like valley.
There are some bright curved ridges on the floor. On the W. of Billy
and Hansteen is a wide inlet of the Oceanus Procellarum, bounded by
the Letronne region on the W., and on the S. by lofty highlands. On the
surface, not far from the S.W. border of Hansteen, is a curious
triangular-shaped mountain mass, with a digitated outline on the S., and
including a small bright crater on its area. Between this and the ring-
plain is a large but somewhat obscure depression, N. of which lies a
rill-like object extending from the N. point of the triangular mountain
to the W. wall. At the bottom of a gently sloping valley between Billy
and Hansteen is a delicate marking, which seems to represent a cleft
connecting the two formations.
ZUPUS.--A formation about 12 miles in diameter with a dark floor,
situated in the hilly region N.E. of Mersenius.
FONTANA.--A noteworthy ring-plain, about 20 miles in diameter, E.N.E. of
Zupus, with a bright border, exhibiting a narrow gap on the S. and two
large contiguous craters on the N.W. The faint central mountain stands on
a dusky interior. On the N. is a large peculiar depressed plain with a
gently sloping wall, within which are three short rill-like valleys and a
crater.
MERSENIUS.--With its extensive rill-system and interesting surroundings,
one of the most notable ring-plains in the third quadrant. It is 41 miles
in diameter, and is encircled by a fine rampart, which on the side
fronting the Mare Humorum rises 7000 feet above the floor, which is
distinctly convex, and is depressed 3000 feet below the region on the E.,
though it stands considerably above the level of the Mare. The
prominently terraced border is tolerably regular on the N.W., but on the
S. and S.E. is much broken by craters and depressions, the largest and
most conspicuous interrupting the continuity of its summit-ridge on the
latter side. A fine crater-row traverses the central part of the
interior, nearly axially, and a delicate cleft crosses the N. half of the
floor from the inner foot of the N.E. wall to a crater not far from the
opposite side. I detected another cleft on November 11, 1883, also
crossing the N. side of the floor.
South of Mersenius is the fine ring-plain Mersenius _d_, about 20 miles
in diameter, situated on the border of the Mare; and, extending in a line
from this towards Vieta are two others (_a_, and Cavendish _d_,),
somewhat larger, but otherwise similar; the more easterly being connected
with Cavendish by a mountain arm. One of the principal clefts of the
system (all of which run roughly parallel to the N.E. side of the Mare,
and extend to the Percy Mountains E. of Gassendi) crosses the floor of
_d_, and, I believe, partially cuts into its W. wall. Another, the
coarsest, abuts on a mountain arm connecting _d_ with Mersenius, and,
reappearing on the E. side, runs up to the N.W. wall of the other ring-
plain, _a_, and, again reappearing on the E. of this, strikes across the
rugged ground between _a_ and Cavendish _d_, traversing its floor and
border, as does also another cleft to the N. of it. Cavendish _d_
includes a coarse cleft on its floor, running from N. to S., which I have
frequently glimpsed with a 4 inch achromatic. There are two other
delicate clefts running from the Gassendi region to the S.W. side of
Mersenius, which are in part crater-rills.
CAVENDISH.--A notable ring-plain, 32 miles in diameter, S.E. of
Mersenius, with a prominently terraced border, rising at one point on the
S. to a height of 6000 feet above the interior, on which are a few low
ridges. A large bright ring-plain (_e_), about 12 miles in diameter,
breaks the continuity of the S.E. wall, and adjoining this, but beyond
the limits of the formation, is another smaller ring with a central hill.
There is also a bright crater on the N.W. border. The W. _glacis_ is very
broad, and includes two large shallow depressions. An especially fine
valley runs up to the N. wall, to the W. side of _e_.
VIETA.--One of the finest objects in the third quadrant; a ring-plain 51
miles in diameter, with broad lofty walls, a peak on the west rising to
nearly 11,000 feet, and another N. of it to considerably more than 14,000
feet above the interior. It is bounded by a linear border, approximating
very closely to an hexagonal shape, which is broken by many gaps and
cross-valleys. On the S., the S.W. and S.E. sections of the wall do not
meet, being separated by a wide valley flanked on the W. by a fine
crater, which has broken down the rampart at this place. The N. border is
likewise intersected by valleys and by a crater-row. The inner slopes are
conspicuously terraced. There is a very inconspicuous central mountain
and several large craters on the floor, some of them double. Ten have
been counted on the N. half of the interior. On the S.E. of Vieta are two
fine overlapping ring-plains, with a crater on the wall common to both.
DE VICO.--A conspicuous little ring-plain, about 9 miles in diameter,
with a lofty border, some distance E. of Mersenius.
LEE.--An incomplete walled-plain, about 28 miles in diameter, on the S.
side of the Mare Humorum, E. of Vitello, from which it is separated by
another partial enclosure, with a striking valley, not shown in the
published maps, running round its W. side. If viewed when its E. wall is
on the morning terminator, some isolated relics of the wrecked N.W. wall
of Lee are prominent, in the shape of a number of attenuated bright
elevations separated by gaps. Within are three or four conspicuous hills.
DOPPELMAYER.--Under a high sun this large ring-plain, 40 miles in
diameter, resembles a great bay open to the N.W., without a trace of
detail to break the monotony of the surface on the side facing the Mare
Humorum. When, however, it is viewed under oblique morning illumination,
a low broad ridge is easily traceable, extending across the opening,
indicating the site of a ruined wall. There is an isolated mountain at
the S.W. end of this, which casts a fine spire of shadow across the floor
at sunrise. The interior contains a massive bright central mountain and
several little hills. The crest of the wall on the E. is much broken.
FOURIER.--A large ring-plain, 30 miles in diameter, S.W. of Vieta, with a
border rising at a peak on the W. more than 9000 feet above the floor,
There are two craters on the outer slope of the N.W. wall, a prominent
crater on the S. wall, and (according to Schmidt) a small central crater
on the floor, which I have not seen. In the region between Fourier and
Vieta there are three ring-plains, two (the more westerly) standing side
by side, and on the W., towards the Mare, are two others much larger,
that nearer to Fourier being traversed by one cleft, and the other by two
clefts, crossing near the centre of the floor.
CLAUSIUS.--A small bright ring-plain in an isolated position N.W. of
Schickard, with a crater both on its N. and S. rim, and a faint central
hill.
LACROIX.--A ring-plain 20 miles in diameter, N. of Schickard. It has a
prominent central mountain.
SCHICKARD.--One of the largest wall-surrounded plains on the visible
surface of the moon, extending about 134 miles from N. to S., and about
the same from E. to W., enclosing a nearly level area, abounding in
detail. Its border, to a great extent linear, is very irregular, and much
broken by the interposition of small ring-plains and craters, and on the
N. by cross-valleys. Its general height is about 4000 feet, the loftiest
peak on the W. wall rising to more than 9000 feet above the floor. The
inner slopes of this vast rampart are very complex, especially on the E.,
where many terraces and depressions may be seen under suitable
illumination. There are three large ring-plains in the interior, all of
them S. of the centre; and at least five smaller ones near the inner foot
of the E. wall, which can only be well observed when libration is
favourable. The two more easterly of the large ring-plains are connected
by a cleft, and there are several short clefts and crater-rows associated
with the smaller ring-plains. On the N. side of the area is a number of
minute craters. The floor is diversified by two large dark markings--an
oblong patch on the S.W. side, abutting on the wall, being the more
remarkable; and a dusky area, occupying a great portion of the N. part of
the floor, and extending up to the N. border. This is traversed by a
light streak running from N. to S., which is the site of a row of minute
craters.
LEHMANN.--A ring-plain, about 28 miles in length, on the N. of Schickard,
with which it is connected by a number of cross-valleys.
DREBBEL.--A bright ring-plain, 18 miles in diameter, on the N.W. of
Schickard, with a lofty irregular border (especially on the W.),
exhibiting a well-marked terrace on the E., a distinct gap on the N., and
a small crater on the S.E. rim. On a dusky area between it and Schickard
stand three prominent deep craters.
PHOCYLIDES.--This extraordinary walled plain, with its neighbouring
enclosures, is structurally very remarkable and suggestive. It consists
of a large irregular formation, with a lofty wall, flanked on the N. by a
smaller and still more irregular enclosure (_b_), the floor of which is
1500 feet above that of Phocylides, the line of partition being a high
cliff, probably representing a "fault," whose shadow under a low sun is
very striking. Phocylides is about 80 miles in maximum length, or, if we
reckon the small enclosure _b_ to form a part of it, more than 120 miles.
The loftiest peak, nearly 9000 feet, is on the W. border, near the
partition wall. The continuity of the rampart is broken on the S. by a
large crater. There is a bright ring-plain on the W. side of the floor,
and a few small craters. Phocylides _b_ has only a solitary crater within
it. Phocylides C, abutting on the W. flank of Phocylides, is about 26
miles in diameter. Its somewhat dusky interior is devoid of detail, but
the outer slope of its W. wall is crowded with a number of minute
craters, which, under good conditions, may be utilised as tests of the
defining power of the telescope used. Phocylides A, on the bright S.W.
plain, is a large deep crater with a fine crater-row flanking it on the
W.
WARGENTIN.--A most remarkable member of the Phocylides group, flanking
the S.E. side of Schickard. Unlike the majority of lunar formations, its
floor is raised considerably above the surrounding region, so that it
resembles a shallow oval dish turned upside down. It is 54 miles in
diameter, and, except on the S.W. (where it abuts on Phocylides _b_, and
for some distance is bounded by its wall), it has only a border of very
moderate dimensions. On the N.E. slope of this ghostly rampart I have
seen a distinct little crater, and two much larger depressions on the
N.W. slope. There are some low ridges on the floor, radiating from a
nearly central point, which have been aptly compared to a bird's foot.
SEGNER.--A fine ring-plain, 46 miles in diameter, on the S.E. side of
Schiller, with a linear border on every side except the N. At a peak on
the W., whose shadow is very remarkable, it rises to a height of more
than 8000 feet above the outer surface. There is a crater on the S.W.
wall, another on the N.W. wall, and several depressions on the outer
slope on this side. The central mountain is small but conspicuous. A
large unnamed enclosure extends N. of Segner: it is larger than Schiller,
and is surrounded by a lofty barrier. The bright plain between this and
the latter is worth examination under a low sun.
ZUCHIUS.--Is situated on the S.E. of Segner, which it slightly overlaps.
It is very similar in size and general character, and has a lofty
terraced wall, rising at one place on the W. to nearly 11,000 feet above
the floor. A very fine chain of craters, well seen when the opposite
border is on the morning terminator, runs round the outer W. slope of the
wall. There is a bright crater beyond this on the S.W. Zuchius has a
central peak.
BETTINUS.--Another ring-plain of the same type and size, some distance S.
of the last, with a massive border, terraced within, and rising on the W.
more than 13,000 feet above the floor, on which stands a grand central
mountain, whose brilliant summit is in sunlight a long time before a ray
reaches any part of the deep interior.
KIRCHER.--A ring-plain, about 45 miles in diameter, S. of Bettinus,
remarkable also for its very lofty rampart, which on the S. attains the
tremendous height of nearly 18,000 feet above the floor, which appears to
be devoid of detail.
WILSON.--The most southerly of the chain of five massive ring-plains,
extending in an almost unbroken line from Segner and differing only very
slightly in size. It is about 40 miles in diameter, and has a somewhat
irregular border, both as regards shape and height, rising at one peak on
the S.W. to nearly 14,000 feet above a level interior, which apparently
contains no conspicuous features.
EAST LONGITUDE 60 deg. TO 90 deg.
GRIMALDI.--This ranks among the largest wall-surrounded plains on the
moon, and is perhaps the darkest. It extends 148 miles from N. to S. and
129 miles from E. to W., enclosing an area of some 14,000 square miles,
or nearly double that of the principality of Wales. This vast dusky
surface is bounded on the E. by a tolerably regular border, having an
average height of about 4000 feet, while on the opposite side it is much
broken, and in places considerably loftier, rising at one peak on the
S.W. to an altitude of 9000 feet. About midway, also, this western
rampart attains a great height, as may be seen by any one who observes at
sunrise the magnificent shadow of it, and its many peaks thrown across
the bluish-grey interior. On the S. the wall is broken by a large
irregular depression, on the W. of which is a very curious V-shaped rill
valley. On the N.W. it is comparatively low, and in places discontinuous;
and even to a greater extent than on the S.W., intersected by passes. At
the extreme N. end, a number of wide valleys cut through the wall and
trend towards Lohrmann. There is a considerable ring-plain at the inner
foot of the N.E. wall, but, except this and a few longitudinal ridges,
just visible under a very low sun, there is apparently no other object to
vary the monotony of this great expanse.
DAMOISEAU.--Consists of a complex arrangement of rings, an enclosure 23
miles in diameter, with a somewhat smaller enclosure placed excentrically
within it (the N. side of both abutting on a bright plateau), with two
large depressions intervening between their W. borders. This peculiarity,
almost unique, renders the formation an especially interesting object.
Damoiseau is situated on the W. side of Grimaldi, on the E. coast-line of
the Oceanus Procellarum, from which the S.W. border rises at a gentle
inclination. On the N.W. there is a curious curved inflexion of the Mare,
bounded by a bright cliff, representing probably the E. side of a
destroyed ring, a supposition which is strengthened by the existence of a
faint scar on the surface of the sea, extending in a curve from one
extremity of the bay to the other, and thus indicating the position of
the remainder of the ring. A conspicuous little crater stands at the S.
end of it, and two others some distance to the W. The smaller component
of Damoiseau contains a low central ridge.
RICCIOLI.--An immense enclosure, near the limb, N.E. of Grimaldi, bounded
by a rampart which is very irregular both in form and height, though
nowhere of great altitude, and much broken by narrow gaps. It is
especially low and attenuated on the N., where a number of ridges with
intervening valleys traverse it. On the S. also a wide valley cuts
through it. With the exception of a few low rounded hills and ridges, a
short crater-row under the S.E. wall, and two small craters on the S.W.,
there are no details on the floor, which, however, is otherwise
remarkable for the dusky tone of its surface, especially on the N. This
dark patch occupies the whole of the N.E. side of the interior, and is
bounded on the S. by an irregular outline, extending at one point nearly
to the centre, and on the W. by a curved edge. The W. side is much darker
than the rest. It is, in fact, as dark, if not darker, than any part of
the floor of Grimaldi. Riccioli extends 106 miles from N. to S., and is
nearly as broad. It includes an area of 9000 square miles.
ROCCA.--An irregular formation, 60 miles in length, near the limb S.E. of
Grimaldi, consisting of a depression partially enclosed by mountain arms.
SIRSALIS.--The more westerly of a conspicuous pair of ring-plains about
20 miles in diameter, in the disturbed mountain region some distance S.W.
of Grimaldi. It has lofty bright walls, rising to a great height above a
depressed floor, on which there is a prominent central mountain. The E.
border encroaches considerably on the somewhat larger companion, which
is, however, scarcely a third so deep. One of the longest clefts on the
visible surface runs immediately W. of this formation. Commencing at a
minute crater on the N. of it, it grazes the foot of the W. _glacis_;
then, passing a pair of small overlapping craters (resembling Sirsalis
and its companion in miniature), it runs through a very rugged country to
a ring-plain E. of De Vico (De Vico _a_), which it traverses, and, still
following a southerly course, extends towards Byrgius, in the
neighbourhood of which it is apparently lost at a ridge, though Schmidt
and Gaudibert have traced it still farther in the same direction. It is
at least 300 miles in length, and varies much in width and character,
consisting in places of distinct crater-rows.
CRUGER.--A regular ring-plain E. of Fontana, 30 miles in diameter, with a
dark floor, without detail, and comparatively low bright walls. There is
a smaller but very conspicuous ring-plain (Cruger _a_) on the W. of it,
to which runs a branch of the great Sirsalis cleft.
EICHSTADT.--A ring-plain, 32 miles in diameter, near the E. limb, S. of
Rocca. It is the largest and most southerly of three nearly circular
enclosures, without central mountains or any other details of interest.
On the W. lies a great walled-plain with a very irregular border,
containing several ring-plains and craters, and a crater-rill. Schmidt
has named this formation DARWIN.
BYRGIUS.--A very irregular enclosure, about 40 miles in diameter, between
Cavendish and the E. limb, with a lofty and discontinuous border, rising
at one point on the E. to a height of 7000 feet above the floor. There
are wide openings both in the N. and S. wall, and some ridges within. The
border is broken on the E. by a crater, and on the W. by the well-known
crater Byrgius A, from which a number of bright streaks radiate, mostly
towards the E. One on the W. extends to Cavendish, and another to
Mersenius, traversing the ring-plain Cavendish C. North-east of Byrgius
there is a mountain arm which includes a peak 13,000 feet in height.
PIAZZI.--A walled-plain, about 90 miles in length, some distance S.E. of
Vieta, with a complex broken border, including several depressions on the
N.W., rising to about 7000 feet above a rather dark interior, on which
there is a prominent central mountain.
LAGRANGE.--A larger but similar formation, 100 miles in diameter,
associated with the last on the N.E., with a complex terraced border,
including peaks of 9000 feet, a bright crater on the W., and a ring-plain
on the N.W. The inner slope of the E. wall is a fine object at sunrise,
when libration is favourable. The floor is dark and devoid of detail.
BOUVARD.--A great irregular enclosure, which appears to be still larger
than Lagrange, S.E. of Piazzi, and close to the limb. It is bounded by a
very lofty rampart, rising at a peak on the W. to 10,000 feet. It has a
fine central mountain.
INGHIRAMI.--A very remarkable ring-plain, 60 miles in diameter, E. of
Schickard, with a bright, broad, and nearly continuous border, terraced
within, and intersected on the N.E. by narrow valleys, one of which is
prolonged over the floor and extends to the central mountain. There are
two curious dark spots on the N. side of the interior. Beyond the foot of
the _glacis_ on the S. a distinct cleft runs from a dusky spot to a group
of small craters E. of Wargentin. There is a fine regular ring-plain with
a small central mount W. of Inghirami.
PINGRE.--A ring-plain, about 18 miles in diameter, between Phocylides and
the limb.
HAUSEN.--A ring-plain, close to the limb, N. of Bailly, which, but for
its position, would be a fine object. It is, however, never sufficiently
well placed for observation.
BAILLY.--One of the largest wall-surrounded plains on the moon, almost a
"sea" in miniature, extending 150 miles from N. to S., and fully as much
from W. to E. When caught at a favourable phase, it is, despite its
position, especially worthy of scrutiny. The rampart on the W., of the
linear type, is broken by several bright craters. On the S.W. two
considerable overlapping ring-plains interfere with its continuity. On
the S.E. several very remarkable parallel curved valleys traverse the
border. The E. wall, which at one point attains a height of nearly 15,000
feet, is beautifully terraced. The floor on the eastern side includes
several ring-plains (some of which are of a very abnormal type), many
ridges, and two delicate dark lines, crossing each other near the S. end,
probably representing clefts.
LEGENTIL.--A large walled-plain, close to the limb, S. of Bailly.
FOURTH QUADRANT
WEST LONGITUDE 90 deg. TO 60 deg.
KASTNER.--A large walled-plain at the S. end of the Mare Smythii, too
near the limb for satisfactory observation.
MACLAURIN.--The principal member of a group of irregular ring-plains on
the W. side of the Mare Foecunditatis, a little S. of the lunar equator.
Schmidt shows no details within it, except a small crater on the E. side
of the floor.
WEBB.--A ring-plain E. of Maclaurin, about 14 miles in diameter, with a
dusky floor, enclosed by a bright rim, on the N.E. side of which there is
a small crater. Schmidt seems to have overlooked the central hill.
LANGRENUS.--This noble circumvallation, the most northerly of the
meridional chain of immense walled-plains, extending for more than 600
miles from near the equator to S. lat. 40 deg., would, but for its
propinquity to the limb, rank with Copernicus (which in many respects it
resembles) among the most striking objects on the surface of the moon.
Its length is about 90 miles from N. to S., and its breadth fully as
much. In shape it approximates very closely to that of a foreshortened
regular hexagon. The walls, which at one point on the E. rise to an
altitude of nearly 10,000 feet, are continuous, except on this side,
where they are broken by the interference of an irregular depression, and
on the extreme S., where they are intersected by cross-valleys. Within,
the terraces are remarkably distinct, and the intervening valleys
strongly marked. The brilliant compound central mountain rises at its
loftiest peak to a height of more than 3000 feet. On the N. of it is an
obscure circular ring, which may possibly merely represent a fortuitous
combination of ridges, though it has all the appearance of a modified
ring-plain. On the Mare, some distance N.E. of the formation, is a group
of three ring-plains, with two small craters (associated with a ridge) on
the N. of them. Two of the more westerly of these objects have prominent
central mountains, and the third a very dark interior. At least three
bright streaks originate on the E. flank of Langrenus, which, diverging
widely, traverse the Mare Foecunditatis.
[FLATTENINGS ON THE MOON'S WESTERN LIMB.--About thirty years ago, the
Rev. Henry Cooper Key drew attention to certain flattenings which he had
noted on the W. limb, which are very apparent under favourable conditions
of libration. Their position cannot be closely defined, but the principal
deviation from circularity extends from about S. lat. 10 deg. to the
region on the limb opposite the S. border of the Mare Crisium.]
VENDELINUS.--The second great enclosure pertaining to the meridional
chain--a magnificent walled-plain of about the same dimensions as the
last. It is bounded by a very irregular rampart, which, under evening
illumination, is especially noteworthy, though nowhere approaching the
altitude of that of Langrenus. Its continuity on the W. is broken by the
great ring-plain Vendelinus C, about 50 miles in diameter, a formation
resembling Langrenus in miniature. This is hexagonal in shape, and has
many rings and depressions on its W. wall. South of Vendelinus C, the
wall of Vendelinus runs up in a bold curve to the fine terraced ring-
plain Vendelinus B, and is surmounted by a bright serpentine crest, and
traversed by several valleys running down the slope to the floor. B has a
small crater on its N. wall, and another in the interior. There is a wide
gap in the S. border of Vendelinus, which is partially occupied by
another somewhat smaller ring-plain, bounded by a southerly extension of
the E. wall, which includes on its outer slope many craters and other
depressions, and abuts near its N. end on the large ring-plain Vendelinus
A, which has a prominently terraced wall and a large bright central
mountain. Between A and C extends a plateau that may be regarded as the
N. limit of the formation, including, among other minor details, a fine
cleft, which traverses it from N. to S., and ultimately extends to a
group of craters on the floor. On the S. side of the interior is one
large ring-plain, flanked on the W. by two small craters. Near the N. end
are many bright little craters, many of them unrecorded. Vendelinus C is
bordered on the E. by two large semicircular formations with low walls
extending on to the floor. Mr. W.H. Maw and others have detected many
minute depressions in connection with these curious objects; and N. of
them, on the outer slope of C, where it runs out to the level of the
plateau, I have seen the surface at sunset riddled like a sieve with
craterlets and little pits. There is an irregular ring-plain N. of A,
with linear walls, and another, much smaller and brighter, on the N. of
this, standing a little beyond the N. limits of Langrenus.
LA PEYROUSE.--A much foreshortened walled-plain, 41 miles in diameter,
close to the limb, S.W. of Langrenus. There is a longitudinal ridge on
the floor. Between it and Langrenus are two large ring-plains with
central mountains, and on the N.E., La Peyrouse A, a bright crater,
adjoining which is La Peyrouse DELTA, one of the most brilliant spots on
the moon.
ANSGARIUS.--A ring-plain, 50 miles in diameter, still nearer to the limb
than the last.
BEHAIM.--A great ring-plain, 65 miles in diameter, S. of Ansgarius, and
connected with it by ridges. It has lofty walls and a central mountain.
HECATAEUS.--An immense walled-plain, 115 miles in length, on the S.W. of
Vendelinus, with a very irregular rampart and a conspicuous central
mountain. It is flanked E. and W. by other large enclosures, which can
only be seen to advantage when libration is favourable.
W. HUMBOLDT.--Though close to the limb, this enormous wall-surrounded
plain, some 130 miles in extreme length, and estimated to have an area of
12,000 square miles, is well worth observing under suitable conditions.
It ranks among the largest formations of its class, and in many respects
resembles Bailly on the S.E. limb. At one point on the E. a peak rises to
16,000 feet, and on the opposite side there are peaks nearly as high. The
floor contains some detail--a crater, nearly central, associated with
ridges, and two dark spots, one at the S. and the other at the N. end.
PHILLIPS.--Abuts on the E. side of W. Humboldt. It is a walled-plain,
about 80 miles in length, with a border much broken on the E., and
terraced within on the opposite side. There are many hills and ridges on
the floor.
LEGENDRE.--A fine ring-plain, 46 miles in diameter, on the S.E. of the
last. According to Schmidt, there is a crater on the S. side of the
floor. There is a small ring-plain, ADAMS, on the S.
PETAVIUS.--The third member of the great meridional chain: a noble
walled-plain, with a complex rampart, extending nearly 100 miles from N.
to S., which encloses a very rugged convex floor, traversed by many
shallow valleys, and includes a massive central mountain and one of the
most remarkable clefts on the visible surface. To observe these features
to the best advantage, the formation should be viewed when its W. wall is
on the evening terminator. At this phase a considerable portion of the
interior on the N. is obscured by the shadow of the rampart, but the
principal features on the S. half of the floor, and on the broad gently-
shelving slope of the W. wall, are seen better than under any other
conditions. The border is loftiest on the E., where the ring-plain
Wrottesley abuts on it. It rises at this point to nearly 11,000 feet,
while on the opposite side it nowhere greatly exceeds 6000 feet above the
interior. The terraces, however, on the W. are much more numerous, and,
with the associated valleys, render this section of the wall one of the
most striking objects of its class. The N. border is conspicuously broken
by the many valleys from the region S. of Vendelinus, which run up to and
traverse it. On the S., also, it is intersected by gaps, and in one place
interrupted by a large crater. There is a remarkable bifurcation of the
border S. of Wrottesley. A lower section separates from the main rampart
and, extending to a considerable distance S.E. of it, encloses a wide and
comparatively level area which is crossed by two short clefts. The
central mountains of Petavius, rising at one peak to a height of nearly
6000 feet above the floor, form a noble group, exceeding in height those
in Gassendi by more than 2000 feet. The convexity of the interior is such
that the centre of it is about 800 feet higher than the margin, under the
walls; a protuberance which would, nevertheless, be scarcely remarked _in
situ_, as it represents no steeper gradient than about 1 in 300 on any
portion of its superficies. The great cleft, extending from the central
mountains to the S.E. wall, and perhaps beyond, was discovered by
Schroter on September 16, 1788, and can be seen in a 2 inch achromatic.
In larger instruments it is found to be in places bordered by raised
banks.
WROTTESLEY.--A formation, about 25 miles in diameter, closely associated
with the E. wall of Petavius, the shape of which it has clearly modified.
Its border on the E., of the linear type, rises nearly 9000 feet above a
light interior, where there is a small bright central mountain and some
mounds. There is a prominent valley running along the inner slope of the
W. wall.
PALITZSCH.--If this extraordinary formation is observed when the moon is
about three days old, it resembles a great trough, or deep elongated
gorge flanking the W. wall of Petavius, though it is a true ring-plain,
albeit of a very abnormal type, about 60 miles in length and 20 miles in
breadth, with a somewhat dusky interior. On the outer slope of its W.
wall is a bright ring-plain with a lofty border and a central mountain.
HASE.--An irregular formation, about 50 miles in diameter, on the S.W. of
Petavius, with which it is connected by extensions of the W. and E. walls
of the latter. Its rampart, some 7000 feet above the floor, is broken by
depressions on the W.; and on the S. is bounded by a smaller ring-plain
with still loftier walls. Schmidt shows a large crater and three smaller
ones on the W. side of the floor.
MARINUS.--A ring-plain on the N.E. side of the Mare Australe, between
Furnerius and the limb.
FURNERIUS.--The fourth and most southerly component of the great
meridional chain of walled-plains, commencing on the N. with Langrenus: a
fine but irregular enclosure, about 80 miles in extreme length and much
more in breadth. Its rampart is very lofty, and tolerably continuous on
the N. and W., but on the other sides is interrupted by small craters and
depressions. At peaks on the E. it attains a height of more than 11,000
feet above the interior, and there are other peaks rising nearly as high.
There is a ring-plain (Furnerius B) with a central hill, on the E. side
of the floor, and numerous craters and crater-pits in other parts of it.
On the N.W. side of B there is a short cleft, on the W., a well-marked
crater-row, and on the E. a long rill-valley. The very brilliant crater
(Furnerius A) on the N.E. _glacis_ is the origin of two fine light
streaks, one extending S. for more than 100 miles, and the other in the
opposite direction for a great distance.
FRAUNHOFER.--A ring-plain, S. of Furnerius, about 30 miles in diameter,
with a regular border rising about 5000 feet above the floor. A smaller
ring-plain abuts on the N.E. side of it, which has slightly disturbed its
wall.
OKEN.--A large enclosure in S. lat. 43 deg. with broken irregular walls.
It is too near the limb for observation.
VEGA.--Schmidt represents this peculiar formation, situated S.E. of Oken,
as having a regular curved unbroken rampart on the E., while the opposite
border is occupied by four large partially overlapping ring-plains, two
of which contain small craters. The floor is devoid of detail.
PONTECOULANT.--A great irregular walled plain, about 100 miles in length,
near the S.W. limb, with a border rising in places to a height of 6000
feet above the floor.
HANNO.--A smaller and more regular enclosure, adjoining Pontecoulant on
the N.W., and still nearer the limb.
WEST LONGITUDE 60 deg. TO 40 deg.
MESSIER.--The more westerly of a remarkable pair of bright craters, about
9 miles in diameter, standing in an isolated position in the Mare
Foecunditatis just S. of the Equator. Madler represents them as similar
in every respect, but Webb, observing them in 1855 and 1856 with a 3 7/10
achromatic, found them very distinctly different,--Messier, the more
westerly, being not only clearly smaller than its companion, but longer
from W. to E. than from N. to S., as it undoubtedly is at the present
time. Messier A, however, as the companion is termed, though larger, is
certainly not circular, as sometimes shown, but triangular with curved
sides. It is just possible that change may have occurred here, for Madler
carefully observed these objects more than three hundred times, and, it
may be presumed, under very different phases. Messier A is the origin of
two slightly divergent light streaks, resembling a comet's tail, which
extend over the Mare towards its E. border N. of Lubbock, and are crossed
obliquely by a narrower streak. Messier and Messier A stand near the S.
and narrowest end of a tapering curved light area. There is a number of
craterlets and minute pits in the neighbourhood, and under a high light
two round dusky spots are traceable in connection with the "comet"
marking, one just beyond its northern, and the other beyond its southern
border, near its E. extremity.
LUBBOCK.--A brilliant little crater, about 4 or 5 miles in diameter, near
the E. coast-line of the Mare Foecunditatis. The region E. of this object
is particularly well worthy of scrutiny under a low sun, on account of
the variety of detail it includes. On the S.E. run three fine parallel
clefts, originating near the N. end of the Pyrenees.
GUTTEMBERG.--A very fine ring-plain of peculiar shape, about 45 miles in
width, with a lofty wall, broken on the N.W. by another ring-plain some
14 miles in diameter, and on the S.E. by a small but distinct crater. The
border presents a wide opening towards the S., which is traversed by a
number of longitudinal valleys, both the E. and W. sections of the wall
being prolonged in this direction. A fine crater-row runs round the outer
slope of the E. wall, from the crater just mentioned to the N. side of
the formation. It is best seen when the W. wall is on the evening
terminator. There is also a broad valley on the S. prolongation of the W.
wall. The central mountain is bright but not large. A cleft crosses the
N.W. side of the floor. North of Guttemberg there is a curious oblong
formation with low walls, connected with the N.E. border by a ridge, and
with the N. border by a remarkable row of depressions, situated on a
mound; and beyond this object on the E. are three parallel clefts running
towards the N.E. On the W. will be found some of the clefts belonging to
the Goclenius rill-system. In the rugged region S.E. of the formation is
a peculiar low ring with a very uneven floor and a large central hill.
The E. wall of Guttemberg may be regarded as forming a portion of the
Pyrenees Mountains.
GOCLENIUS.--A ring-plain, about 28 miles in diameter, bearing much
resemblance to Plinius in form and size, and, like this formation,
associated with a fine system of clefts. The lofty rampart, tolerably
continuous on the W., is broken on the S.W. by a bright crater, and on
the N.W. by a remarkable triangular depression. It is also traversed by a
delicate valley extending from the crater on the S.W. to another on the
N.W. border; and at a point a little W. of the first crater is dislocated
by an intrusive mass of rock. There are several gaps on the E. and many
spurs and irregularities in outline both within and without. A great
portion of the N. wall is linear, and joins the E. section nearly at
right angles. West of the triangular depression it appears to be
partially wrecked, indications of the destruction being very evident if
it be observed when the E. wall is near the morning terminator. The small
bright central mountain is remarkable for its curious oblong shadow. Two
clefts traverse the interior of Goclenius. (1) Originates at the S. wall,
E. of the crater, and runs E. of the central mountain to the N. wall; (2)
crosses the _debris_ of the ruined N.W. border, runs parallel to the
first, and extends nearly to the centre of the floor, (1) Re-appears at
the foot of a mound outside the N. wall, and, after crossing the outer W.
slope of the great ring-plain on the N.W. wall of Guttemberg, runs to the
W. side of an oblong formation N. of it. There are two other clefts,
closely parallel and W. of this, traversing the Mare, and terminating
among the mountains on the N.W. These are crossed at right angles by what
appears to be a "fault," running in a N.W. direction from the W. side of
Guttemberg.
MACCLURE.--One of a curious group of formations situated in the Mare
Foecunditatis some distance S.W. of Goclenius. It is a bright ring-plain,
about 15 miles in diameter, with a narrow gap in the N.E. wall and a
small central hill. A prominent ridge runs up to the N. border; and on
the S.W. a rill-valley may be traced, extending S. to a bright deep
little crater W. of Cook.
CROZIER.--A conspicuous ring-plain a few miles N.N.W. of MacClure, and of
about the same size. It has a faint central hill. Neison refers to two
long straight streaks extending from Crozier towards Messier.
BELLOT.--A brilliant little ring-plain N.E. of Crozier.
COOK.--A ring-plain, about 25 miles in diameter, on the E. side of the
Mare Foecunditatis in S. lat. 17 deg., with low and (except on the S.E.)
very narrow walls. There is a small circular depression on the S. border,
and a prominent crater on the W. side of the dark interior. On the S.S.E.
is the curiously shaped enclosure Cook _d_, with very bright broad lofty
walls and a fine central mountain. On the plain W. of Cook is a
conspicuous crater-row, consisting of six or seven craters, diminishing
in size in both directions from the centre.
COLOMBO.--A fine ring-plain, about 50 miles in diameter, situated in the
highlands separating the Mare Foecunditatis and the Mare Nectaris. The
wall, rising at one place to a height of 8000 feet above the floor, is
very complicated and irregular, being traversed within by many terraces,
and almost everywhere by cross-valleys. Its shape is greatly distorted by
the large ring-plain _a_, which abuts on its N.E. flank. It loses its
individuality altogether on the S., its place being occupied by two large
depressions, and lofty mountains trending towards the S.E. In the centre
there are several distinct bright elevations.
MAGELHAENS.--The more northerly and the larger of a pair of ring-plains
between Colombo and Goclenius, with a bright and somewhat irregular
though continuous border. The dark interior includes a small central
mountain. Its companion on the S.W., Magelhaens _a_, slightly overlaps
it. This also has a central hill, and a crater on the outer slope of its
E. wall.
SANTBECH.--A very prominent ring-plain, 46 miles in diameter, on the S.E.
side of the Mare Foecunditatis, W. of Fracastorius. The continuity of its
fine lofty rampart is broken on the W., where it rises nearly 10,000 feet
above the floor, by a brilliant little crater just below the crest, and
by a narrow gap on the S. The wall on the E. towers to a height of 15,000
feet above the interior. On its broad outer slope, near the summit, there
is a fine crater, and S. of this running obliquely down the slope a
distinct valley. On the N.E., where the _glacis_ runs down to the level
of the surrounding plain, there is a large crateriform object with a
broken N. border, and a small crater opposite the opening. A long coarse
valley runs from this latter object in a N.E. direction to the region W.
of Bohnenberger. Santbech contains a prominent central peak.
BIOT.--A brilliant little ring-plain, scarcely more than 7 miles in
diameter, standing in an isolated position in the Mare Foecunditatis N.E.
of Wrottesley. There is a number of bright streaks in its neighbourhood;
and a few miles E. of it, in the hilly region W. of Santbech, another
conspicuous crater of about the same size.
BORDA.--A ring-plain about 25 miles in diameter, S.S.W. of Santbech, with
a rampart low on the N. and S., but elsewhere of considerable height, and
a very conspicuous central mountain. A wide deep valley flanked by lofty
mountains extends from the N. wall for many miles towards the N.W. It is
an especially noteworthy object when the W. wall of Santbech is on the
evening terminator, as its somewhat winding course, indicated by the
bright summit-ridges of the bordering mountains, can be followed some
hours before either the interior of the valley or the region between it
and Santbech are in sunlight. Among the mountains W. of Borda there is a
peak more than 11,000 feet in height.
SNELLIUS.--A very fine ring-plain, 50 miles in diameter, S.E. of
Petavius, with terraced walls, considerably broken on the S.E. by
craters, &c. It rises on the E. nearly 7000 feet above a dark floor,
which contains a central mountain. N.E. of Snellius is a smaller ring-
plain (Snellius _a_), and due E. a curious rough plateau, bordered on the
N. and S. by a number of small craters.
STEVINUS.--A somewhat larger ring-plain, S. of Snellius, with a border
rising on the S. to more than 11,000 feet above a dark interior, which
includes a bright central mountain.
REICHENBACH.--A very abnormally-shaped ring-plain, about 30 miles in
diameter, with a rampart nearly 12,000 feet high. The border is broken on
the W., S., and E. by craters and depressions, and on the N. is flanked
by two overlapping ring-plains, _a_ and _b_. On the S.W. lies a
magnificent serpentine valley, fully 100 miles in length and about 12
miles in breadth at the N. end, but gradually diminishing as it runs
southwards, till it reaches a depression N. of Rheita, where it
terminates: here is scarcely more than 4 miles wide.
RHEITA.--A formation, about 35 miles in diameter, S. of Reichenbach, with
regular lofty walls, rising at a peak on the N.E. to a height of more
than 14,000 feet above the interior, on which there is a small but
prominent central mountain, a smaller elevation W. of the centre, and two
adjoining craters at the foot of the S. wall. On the E. originates
another fine valley, very similar to that already mentioned in connection
with Reichenbach. It runs in a S.S.W. direction, is about 100 miles in
length, and, in its widest part, is about 12 miles across. Like the
Reichenbach valley, it terminates at a small crater-like object, which
has a border broken down on the side facing the valley, and a small
central hill. About midway between its extremities, this great gorge is
crossed by a wall of rock, like a narrow bridge.
JANSSEN.--An immense irregular enclosure, reminding one of the very
similar area, bordered by Walter, Lexell, Hell, &c., in the third
quadrant. It extends about 150 miles from E. to W., and more than 100
from N. to S., its limits on the N. being rather indefinite. Its very
rugged humpy surface includes one great central mountain, and innumerable
minor hills and ridges, craters, and crater-pits; but the principal
feature is the magnificent curved rill-valley running from the S. side of
Fabricius across the rough expanse to the S. side. This fine object, very
coarse on the N., passes the central mountain on the E. side, and becomes
gradually narrower as it approaches the border; before reaching which,
another finer cleft branches from it on the W., and also runs to the S.
side of the plain.
LOCKYER.--A prominent deep ring-plain, 32 miles in diameter, with massive
bright lofty walls, standing just outside the S.E. border of Janssen.
Schmidt shows a minute crater on the S. rim. I have seen a crater within,
at the inner foot of the W. wall, and a central peak.
FABRICIUS.--A ring-plain, 55 miles in diameter, with a lofty terraced
border, rising on the S.W. to a height of nearly 10,000 feet above the
interior. It is partially included by the rampart of Janssen, and the
great rill-valley on the floor of the latter appears to cut through its
S. wall. There is a long central mountain on the floor, with a prominent
ridge extending along the E. side of it. W. of Fabricius (between it and
the border of Janssen) lies a very irregular enclosure, with three
distinct craters within it; and on the E., running from the wall to the
E. side of Janssen, is a straight narrow valley. Both Fabricius and
Janssen should be viewed under a low morning sun.
STEINHEIL.--A double ring-plain, W. of Janssen, 27 miles in diameter. The
more easterly formation sinks to a depth of nearly 12,000 feet below the
summit of the border.
METIUS.--This ring-plain, of about the same size as Fabricius, but with a
still loftier barrier, abuts on the N. wall of this formation, and has
caused a very obvious deformation in its contour. It is prominently
terraced internally, and on the W. the wall rises at one peak to a height
of 13,000 feet above the floor, which contains a deep crater on the W. of
the centre, and many ridges.
BIELA.--A considerable ring-plain, about 55 miles in diameter, S.W. of
Janssen, with a wall broken on the N.W., S., and E. by rings and large
enclosures. There is a central mountain, but apparently no other details
on the floor.
ROSENBERGER.--This formation, about 50 miles in diameter, is one of the
remarkable group of large rings to which Vlacq, Hommel, Pitiscus, &c.,
belong. Its walls, though of only moderate altitude, are distinctly
terraced. In addition to a prominent central mountain (E. of which
Schmidt shows two craters), there is a large crater on the S. side of the
floor, and many smaller craters and crater-pits.
HAGECIUS.--The most westerly member of the Vlacq group of formations. It
is situated on the S.W. of Rosenberger, and is about 50 miles in
diameter. The rampart on the E. is continuous and of the normal type, but
on the opposite side is broken by a number of smaller rings.
WEST LONGITUDE 40 deg. TO 20 deg.
CENSORINUS.--A brilliant little crater, with very bright surroundings, in
the Mare Tranquilitatis, nearly on the moon's equator, in W. long. 32
deg. 22 min. Another smaller but less conspicuous crater adjoins it on
the W. On the Mare to the S. extends a delicate cleft which trends
towards the Sabine and Ritter rill system.
CAPELLA.--Forms with Isodorus, its companion on the E. (which it
partially overlaps), a very noteworthy object. It is about 30 miles in
diameter, with finely terraced walls, broken on the S.W. by broad
intrusive rill-valleys. The rampart on the N.E. is also cut through by a
magnificent valley, which extends for many miles beyond the limits of the
formation. There is a fine central mountain, on which M. Gaudibert
discovered a crater, the existence of which has been subsequently
verified by Professor Weinek on a Lick observatory negative.
ISODORUS.--The rampart of this fine ring-plain, which is of about the
same size as Capella, rises at a peak on the W. to a height of more than
13,000 feet above the interior, which, except a small bright crater at
the foot of the E. wall and a smaller one adjoining it on the N.,
contains no detail. The region between Isodorus and the equator includes
many interesting objects, among them Isodorus _b_, an irregular formation
open towards the N., and containing several craters.
BOHNENBERGER.--A ring-plain about 22 miles in diameter, situated on the
W. side of the Mare Nectaris, under the precipitous flanks of the
Pyrenees, whose prominent shadows partially conceal it for many hours
after sunrise. The circular border is comparatively low, and, except on
the N., continuous. Here there is a gap, and on the W. of it an intrusive
mass of rock. From its very peculiar shadow at sunrise, the wall on the
E. appears to be very irregular. The club-shaped central mountain is of
considerable size, but not conspicuous. S. of Bohnenberger stands the
very attenuated ring, Bohnenberger A. It is of about the same diameter,
has a large deep crater on its N. rim, and a smaller one, distinguished
with difficulty, on its S.E. rim. On the N. of Bohnenberger there is a
bright little ring-plain connected with the formation by a lofty ridge,
under the E. flank of which Schmidt shows a crater-chain. An especially
fine cleft originates on the E. side of this crater, which, following an
undulating course over the Mare Nectaris, terminates at Rosse, N. of
Fracastorius.
TORRICELLI.--A remarkable little formation in the Mare Tranquilitatis, N.
of Theophilus, consisting of two unequal contiguous craters ranging from
W. to E., whose partition wall has nearly disappeared, so that, under a
low sun, when the interior of both is filled with shadow, the pair
resemble the head of a javelin. The larger, western, ring is about 10
miles in diameter, and the other about half this size. There is a gap in
the W. wall of the first, and a long spur projecting from its S. side;
and a minute crater on the S. border of the smaller object. Torricelli is
partially enclosed on the S. by a circular arrangement of ridges. There
is a delicate cleft running in a meridional direction on the Mare, E. of
the formation, and another on the N., running from W. to E.
HYPATIA.--A ring-plain, about 30 miles in extreme length, of very
abnormal shape, on the E. side of the Mare, N.N.E. of Theophilus, with a
wall rising at a peak on the E. to a height of more than 7000 feet above
a dusky floor, which does not apparently contain any detail. A small
crater breaks the uniformity of the border on the W. Beyond the wall on
the S.E. lies the fine bright crater Hypatia A, with another less
prominent adjoining it on the S.W.
THEOPHILUS.--The most northerly of three of the noblest ring-mountains on
the visible surface of the moon, situated on the N.E. side of the Mare
Nectaris. It is nearly 64 miles in diameter, and is enclosed by a mighty
rampart towering above the floor at one peak on the W. to the height of
18,000 feet, and at two other peaks on the opposite side to nearly 16,000
and 14,000. The border, though appearing nearly circular with low powers,
is seen, under greater magnification, to be made up of several more or
less linear sections, which give it a polygonal outline. It is
prominently terraced within, the loftier terraces on the W. rising nearly
to the height of the crest of the wall, and including several craters and
elongated depressions. On the W. _glacis_ is a row of large inosculating
craters; and near its foot, S.E. of Madler, a short unrecorded rill-
valley. The magnificent bright central mountain is composed of many
distinct masses surmounted by lofty peaks, one of which is about 6000
feet above the floor, and covers an area of at least 300 square miles.
Except a distinct crater on the S.W. quarter, this appears to be the only
object within the ring.
CYRILLUS.--The massive border of Theophilus partially overlaps the N.W.
side of this great walled-plain, which is even more complex than that of
its neighbour, and far more irregular in form, exhibiting many linear
sections. Its crest on the S.E. is clearly inflected towards the
interior, a peculiarity that has already been noticed in connection with
Copernicus and some other objects. On the inner slope of this wall there
is a large bright crater, in connection with which have been detected two
delicate rills extending to the summit. I have not seen these, but one of
the crater-rows shown by Schmidt, between this crater and the crest, has
often been noted. The N.E. wall is very remarkable. It appears to be
partially wrecked. If observed at an early stage of sunrise, a great
number of undulating ridges and rows of hillocks will be seen crossing
the region E. of Theophilus. They resemble a consolidated stream of
"ropy" lava which has flowed through and over the wall and down the
_glacis_. The arrangement of the ridges within Cyrillus is very
noteworthy, as is also the triple mountain near the centre of the floor.
The fine curved cleft thereon traverses the W. side, sweeping round the
central mountains, and then turning to the south. I have only
occasionally seen it in its entirety. There are also two oblong dark
patches on the S. side of the interior. The S. wall of Cyrillus is broken
by a narrow pass opening out into a valley situated on the plateau which
bounds the W. side of the oblong formation lying between it and
Catherina, and overlooking a curious shallow square-shaped enclosure
abutting on the S.W. side of Cyrillus.
CATHERINA.--The largest of the three great formations: a ring-plain with
a very irregular outline, extending more than 70 miles in a meridional
direction, and of still greater width. The wall is comparatively narrow
and low on the N.E. (8000 feet above the floor), but on the N.W. it rises
to more than double this height, and is broken by some large depressions.
The inner slope on the S.E. is very gentle, and includes two bright
craters, but exhibits only slight indications of terraces. The most
remarkable features on an otherwise even interior are the large low
narrow ring (with a crater within it), occupying fully a third of the
area of the floor, and a large ring-plain on the S. side.
MADLER.--The interest attaching to this formation is not to be measured
by its size, for it is only about 20 miles in diameter, but by the
remarkable character of its surroundings. Its bright regular wall, rising
6000 feet on the E. and only about half as much on the W., above a rather
dark interior, is everywhere continuous, except at one place on the N.
Here there is a narrow gap (flanked on the E. by a somewhat obscure
little crater) through which a curious bent ridge coming up from the N.
passes, and, extending on to the floor, expands into something resembling
a central mountain. Under a high sun Madler has a very peculiar
appearance. The lofty E. wall is barely perceptible, while the much lower
W. border is conspicuously brilliant; and the E. half of the floor is
dark, while the remainder, with two objects representing the loftier
portions of the intrusive ridge, is prominently white. Under an evening
sun, with the terminator lying some distance to the W., a very remarkable
obscure ring with a low border, a valley running round it on the W. side,
and two large central mounds, may be easily traced. This object is
connected with Madler by what appears to be under a higher sun a bright
elbow-shaped marking, in connection with which I have often suspected a
delicate cleft. Between the obtuse-angled bend of this object and the W.
wall of Madler, two large circular dark spots may be seen under a high
sun; and on the surface of the Mare N. of it, a great number of delicate
white spots.
BEAUMONT.--A ring-plain about 30 miles in diameter, on the S.E. side of
the Mare Nectaris, midway between Theophilus and Fracastorius, with the
N.E. side of which it is connected by a chain of large depressions. Its
border is lofty, regular, and continuous on the S. and E., but on the W.
it is low, and on the N. sinks to such a very inconsiderable height that
it is often scarcely traceable. It exhibits two breaks on the S.W.,
through one of which passes a coarse valley that ultimately runs on the
E. side of the depressions just referred to. The interior is pitted with
many craters, one on the W. side being shallow but of considerable size.
I once counted twenty with a 4 inch Cooke achromatic, and Dr. Sheldon of
Macclesfield subsequently noted many more. A ridge, prominent under
oblique light, follows a winding course from the N.W. side of Beaumont to
the W. side of Theophilus, and there is another lower ridge E. of it.
Between them is included a region covered with minute hillocks and
asperities. Among these objects are certain dusky little crater-cones,
which Dr. Klein of Cologne regards as true analogues of some terrestrial
volcanoes. They are very similar in character to those, already alluded
to, in the dusky area between Copernicus and Gambart.
KANT.--A conspicuous ring-plain, 23 miles in diameter, situated in a
mountainous district E. of Theophilus, with lofty terraced walls and a
bright central peak. Adjoining it on the W. is a mountain mass,
projecting from the coast-line of the Mare, on which there is a peak
rising to more than 14,000 feet above the surface.
FRACASTORIUS.--This great bay or inflexion at the extreme S. end of the
Mare Nectaris, about 60 miles in diameter, is one of the largest and most
suggestive examples of a partially destroyed formation to be found on the
visible surface. The W. section of the rampart is practically complete
and unbroken, rising at one peak to a height of 6000 feet above the
interior. It is very broad at its S. end, and its inner slope descends
with a gentle gradient to the floor. Towards the N., however, it rapidly
decreases in width, but apparently not in altitude, till near its bright
pointed N. extremity. Under a low sun, some long deformed crateriform
depressions may be seen on the slope, and a bright little crater on the
crest of the border near its N. end. The southern rampart is broken by
three large craters, and a fine valley, running some distance in a S.
direction, which diminishes gradually in width till it ultimately
resembles a cleft, and terminates at a small crater. The E. border is
very lofty and irregular, rising at the N. corner of the large triangular
formation, which is such a prominent feature upon it, to a height of 7000
feet, and at a point on the S.E. to considerably more than 8000 feet
above the floor. N. of the former peak it becomes much lower and
narrower, and is finally only represented by a very attenuated strip of
wall, hardly more prominent than the brighter portions of the border of
Stadius at sunrise, terminating at an obscure semi-ring-plain. Between
this and the pointed N. termination of the W. border there is a wide gap,
open to the north for a space of about 30 miles, appearing, except under
very oblique illumination, as smooth and as devoid of detail as the grey
surface of the Mare Nectaris itself. If, however, this interval is
observed at sunrise or sunset, it is seen to be not quite so
structureless as it appears under different conditions, for a number of
mounds and large humpy swellings, with low hills and craterlets, extend
across it, and occupy a position which we are justified in regarding as
the site of a section of the rampart, which, from some cause or other,
has been completely destroyed and overlaid with the material, whatever
this may be, of the Mare Nectaris. The floor of Fracastorius is, as
regards the light streaks and other features upon it, only second in
interest to those of Plato and Archimedes, and will repay systematic
observation. Between thirty and forty light spots and craters have been
recorded on its surface, most of them, as in these formations, being
situated either on or at the edges of the light streaks. On the higher
portion of the interior (near the centre) is a curious object consisting
apparently of four light spots, arranged in a square, with a craterlet in
the middle, all of which undergo (as I have pointed out elsewhere)
notable changes of aspect under different phases. There are at least two
distinct clefts on the floor, one running from the W. wall towards the
centre, and another on the S.E. side of the interior. The last throws out
two branches towards the S.W.
ROSSE.--A fine bright deep crater in the Mare Nectaris, N. of the pointed
termination of the W. wall of Fracastorius, with which it is connected by
a bold curved ridge, with a crater upon it. A ray from Tycho, striking
along the E. wall of Fracastorius passes near this object. A rill from
near Bohnenberger terminates at this crater.
POLYBIUS.--A ring-plain, about 17 miles in diameter, in the hilly region
S.E. of Fracastorius. The border is unbroken, except on the N., where it
is interrupted by a group of depressions. There is a long valley on the
S.W., at the bottom of which Schmidt shows a crater-chain.
NEANDER.--This ring-plain, 34 miles in diameter, a short distance W.S.W.
of Piccolomini, has a somewhat deformed rampart, which, however, except
on the N., where there is a narrow gap occupied by a small crater, is
continuous. It rises on the E. nearly 8000 feet above the floor, on which
there is a central mountain about 2500 feet high. Schmidt shows some
minor hills, a large crater on the N.E. side, and three smaller craters
in the interior.
PICCOLOMINI.--A ring-plain of a very massive type, about 57 miles in
diameter, S. of Fracastorius, with complex and prominently terraced
walls, surmounted by very many peaks; one of which on the E. attains a
height of 14,000 feet, and another, N. of it, on the same side, an
altitude of 15,000 feet above the interior. The crest of this grand
rampart is tolerably continuous, except on the S.W., where, for a
distance of twenty miles or more, its character as regards form and
brightness is entirely changed. Under a low sun, instead of a continuous
bright border, we note a wide gap occupied by a dusky rugged plateau,
which falls with a gentle gradient to the floor, and is traversed by
three or four parallel shallow valleys running towards the S. I can
recall no lunar formation which presents an appearance at all like this:
one is impressed with the idea that it has resulted from the collapse of
the upper portion of the wall, and the flow of some viscous material over
the wreck and down the inner slope. The difference between the reflective
power of this matter, whatever may be its nature, and the broad bright
declivities of the inner slopes, are beautifully displayed at sunset. The
cross-valleys are more easily traced under low morning illumination; but
to appreciate the actual structure of the wall, it should be observed
under both phases. The N.W. section of the border includes many
"pockets," or long elliptical depressions, which at an early stage of
sunrise give a scalloped appearance to the crest. Except the great bright
central mountain with its numerous peaks, there does not appear to be any
prominent detail on the floor. There is a large ring-plain beyond the
foot of the _glacis_ on the W. with two craters on the E. side of it,
another on the S., and a fine rill-valley running up to its N. side from
near the crest of the W. wall. On the N. side of Piccolomini is a
remarkable group of deformed and overlapping enclosures, mingled with
numberless craters and little depressions. The plain on the N.E. is
crossed by a fine cleft.
PONS.--A complete formation of irregular shape, about 20 miles in
greatest diameter, on the S.E. side of the Altai range, in W. long. 21
deg. It consists of a crowd of rings and craters enclosed by a narrow
wall.
STIBORIUS.--An elongated ring-plain, about 22 miles in diameter, S. of
Piccolomini, with a lofty wall, broken in one place on the N. by a very
conspicuous crater. Schmidt shows a distinct crater in the centre of the
floor. I have only seen a central mountain in this position. There is a
large crater on the N.W., a ring-plain on the S.W. side, and a multitude
of little craters on the surrounding plain.
RICCIUS.--A ring-plain, 51 miles in diameter, of a very irregular type,
S.E. of the last. It is enclosed by a complex wall (which is in places
double), broken by large rings on the S. The very conspicuous little
ring-plain Riccius A is situated on the N. of it, and other less
prominent features. The interior includes a bright crater and some
smaller objects of the same class.
ZAGUT.--The most easterly of a group of closely associated irregular
walled-plains, of which Lindenau and Rabbi Levi are the other members,
all evidently deformed and modified in shape by their proximity. It is
about 45 miles in diameter, and is enclosed by a wall which on the S.W.
attains a height of about 9500 feet, and is much broken on the N. by a
number of depressions. A large ring-plain, some 20 miles in diameter,
occupies a considerable portion of the W. side of the interior; E. of
which, and nearly central, there is a large bright crater, but apparently
no other conspicuous details. On the S.E. side of Zagut lies an
elliptical ring-plain, about 28 miles in diameter, named by Schmidt
CELSIUS. The border of this is open on the N., the gap being occupied by
a large crater, whose S. wall is wanting, so that the interiors of both
formations are in communication.
LINDENAU.--This formation, about 35 miles in diameter, is bounded on the
W. by a regular unbroken wall nearly 8600 feet in height; but which on
the E. and N.E. is far loftier and more complex, rising to about 12,000
feet above the floor, consisting of four or more distinct ramparts,
separated by deep valleys, and extending towards Rabbi Levi. Neison
points out that under a high light Lindenau appears to have a bright
uniform single wall. There is a small central mountain and some minor
inequalities in the interior.
RABBI LEVI.--A larger but less obvious formation than either of its
neighbours, Zagut and Lindenau, abutting on the S. side of them. It is
about 55 miles in diameter, and is enclosed by a border somewhat
difficult to trace in its entirety, except under oblique light. There are
some large craters within it, of which one on the N. side of the floor is
especially prominent.
NICOLAI.--A tolerably regular ring-plain, 18 miles in diameter, S. of
Riccius, with a border, rising more than 6000 feet above a level floor,
on the N. side of which Schmidt shows a minute crater. The bright plain
surrounding this formation abounds in small craters; and on the W. is a
number of curious enclosures, many of them overlapping.
VLACQ.--A member of a magnificent group of closely associated formations
situated on the greatly disturbed area between W. long. 30 deg. and 45
deg. and S. lat. 50 deg. and 60 deg. It is 57 miles in diameter, and is
enclosed by terraced walls, rising on the W. about 8000 feet, and on the
E. more than 10,000 feet above the floor. They are broken on the S. by a
fine crater. In addition to a conspicuous central peak, there are several
small craters, and low short ridges in the interior.
HOMMEL.--Adjoins Vlacq on the S. It is a somewhat larger and a far more
irregular formation. On every side except the W., where the border is
unbroken, and descends with a gentle slope to the dark interior; ring-
plains and smaller depressions encroach on its outline, perhaps the most
remarkable being Hommel _a_ on the N., which has an especially brilliant
wall, that includes a conspicuous central mountain, a large crater, and
other details. The best phase for observing Hommel and its surroundings
is when the W. wall is just within the evening terminator.
PITISCUS.--The most regular of the Vlacq group. It is situated on the
N.E. of Hommel (a curious oblong-shaped enclosure, Hommel _h_, with a
very attenuated E. wall, and a large crater on a floor, standing at a
higher level than that of Pitiscus, intervening). It is 52 miles in
diameter, and is surrounded by an apparently continuous rampart, except
on the E., where there is a crater, and on the S.W., where it abuts on
Hommel _h_. Here there is a wide gap crossed by what has every appearance
of being a "fault," resembling that in Phocylides on a smaller scale.
There is a fine crater on the N. side of the interior connected with the
S. wall by a bright ridge. Just beyond the E. border there is a shallow
ring-plain of a very extraordinary shape.
NEARCH.--A ring-plain, about 35 miles in diameter, on the S.W. of Hommel,
forming part of the Vlacq group.
TANNERUS.--A ring-plain, about 19 miles in diameter, between Mutus and
Bacon. It has a central mountain.
MUTUS.--A fine but foreshortened walled plain, 51 miles in diameter.
There are two ring-plains of about equal size on the floor, one on the
N., and the other on the S. side. The wall on the W. rises to nearly
14,000 feet above the interior.
MANZINUS.--A walled plain, nearly 62 miles in diameter, with a terraced
rampart rising to a height of more than 14,500 feet above the interior.
Schmidt shows three craterlets on the floor, but no traces of the small
central peak which is said to stand thereon, but to be only visible in
large telescopes.
SCHOMBERGER.--A large walled-plain adjoining Simpelius on the S.W. Too
near the limb for satisfactory observation.
WEST LONGITUDE 20 deg. TO 0 deg.
DELAMBRE.--A conspicuous ring-plain, 32 miles in diameter, a little S. of
the equator, in W. long. 17 deg. 30 min., with a massive polygonal
border, terraced within, rising on the W. to the great height of 15,000
feet above the interior, but to little more than half this on the
opposite side. Its outline approximates to that of a pentagon with
slightly curved sides. A section on the S.E. exhibits an inflexion
towards the centre. The crest is everywhere continuous except on the N.,
where it is broken by a deep crater with a bright rim. The north-easterly
trend of the ridges and hillocks on the E. is especially noteworthy. The
central peak is not prominent, but close under it on the E. is a deep
fissure, extending from near the centre, and dying out before it reaches
the S. border. At the foot of the N.E. _glacis_ there are traces of a
ring with low walls.
THEON, SEN.--A brilliant little ring-plain, E.N.E. of Delambre, 11 miles
in diameter, and of great depth, with a regular and perfectly unbroken
wall. North of it is a bright little crater.
THEON, JUN.--A ring-plain similar in size and in other respects to the
last, situated about 23 miles S. of it on a somewhat dusky surface.
Between the pair is a curious oblong-shaped mountain mass; and on the E.
a long cliff (of no great altitude, but falling steeply on the E. side)
extending S. towards Taylor _a_. Just below the escarpment, I find a
brilliant little pair of craterlets, of which Neison only shows one.
ALFRAGANUS.--A large bright crater, about 9 miles in diameter, with very
steep walls, some distance S.S.W. of Delambre, and standing on the W.
edge of a large but very shallow and irregular depression W. of Taylor.
There is a remarkable chain of craters on the W. of it. Alfraganus is the
centre of a system of light streaks radiating in all directions, one ray
extending through Cyrillus to Fracastorius.
TAYLOR.--A deep spindle-shaped ring-plain, S. of Delambre, about 22 miles
in length. The wall appears to be everywhere continuous, except at the
extreme N. and S. ends, where there are small craters. The outer slopes,
both on the E. and W., are very broad and prominent, but apparently not
terraced. There is an inconspicuous central hill. On the W. is the
irregular enclosure, already referred to under Alfraganus. Three or four
short winding valleys traverse the N. edge of this formation, and descend
to the dark floor. On the N.E. is the remarkable ring-plain Taylor _a_,
18 miles in diameter, rising, at an almost isolated mountain mass on the
E. border, to a height of 7000 feet above the interior. The more regular
and W. section of this formation is not so lofty, and falls with a gentle
slope to the dark uneven floor, on which there is some detail in the
shape of small bright ridges and mounds. On the surface, N.W. of Taylor
_a_, is a curious linear row of bright little hills. Taylor and the
vicinity is better seen under low evening illumination than under morning
light.
HIPPARCHUS.--Except under a low sun, this immense walled-plain is by no
means so striking an object as a glance at its representation on a chart
of the moon would lead one to expect; for the border, in nearly every
part of it, bears unmistakable evidence of wreck and ruin, its continuity
being interrupted by depressions, transverse valleys, and gaps, and it
nowhere attains a great altitude. This imperfect enclosure extends 97
miles from N. to S., and about 88 miles from E. to W., and in shape
approximates to that of a rhombus with curved sides. One of the most
prominent bright craters on its border is Hipparchus G, on the W.
Another, of about the same size, is Hipparchus E, on the N. of Horrocks.
On the E. there is a moderately bright crater, Hipparchus F; and S. of
this, on the same side, two others, K and I. The interior is crossed by
many ridges, and near the centre includes the relics of a low ring,
traversed by a narrow rill-like valley. Schmidt shows a cleft running
from F across the floor to the S. border.
[A valuable monograph of Hipparchus, by Mr. W.B. Birt, was published in
1870.]
HORROCKS.--This fine ring-plain, 18 miles in diameter, stands on the N.
side of the interior of Hipparchus, close to the border. It has a
continuous wall, rising on the E. to a height of nearly 8000 feet above
the interior, and a distinct central mountain.
HALLEY.--A ring-plain, 21 miles in diameter, on the S.W. border of
Hipparchus, with a bright wall, rising at one point on the E. to a height
of 7500 feet above the floor, which is depressed about 4000 feet below
the surface. Two craterlets on the floor, one discovered by Birt on
Rutherfurd's photogram of 1865, and the other by Gaudibert, raised a
suspicion of recent lunar activity within this ring. A magnificent
valley, shown in part by Schmidt as a crater-row, runs from the S. of
Halley to the W. side of Albategnius.
HIND.--A ring-plain, 16 miles in diameter, a few miles W. of Halley, with
a peak on its E. wall 10,000 feet above the floor. The border is broken
both on the S.E. and N.E. by small craters.
[Horrocks, Halley, and Hind may be regarded as strictly belonging to
Hipparchus.]
ALBATEGNIUS.--A magnificent walled-plain, 65 miles in diameter, adjoining
Hipparchus on the S., surrounded by a massive complex rampart,
prominently terraced, including many depressions, and crossed by several
valleys. It is surmounted by very lofty peaks, one of which on the N.E.
stands nearly 15,000 feet above the floor. The great ring-plain
Albategnius A, 28 miles in diameter, intrudes far within the limits of
the formation on the E., and its towering crest rises more than 10,000
feet above its floor, on which there is a small central mountain. The
central mountain of Albategnius is more than 4000 feet high, and, with
the exception of a few minor elevations, is the only prominent feature in
the interior, though there are many small craters. Schmidt counted forty
with the Berlin refractor, among them 12 on the E. side, arranged like a
string of pearls.
PARROT.--An irregularly-shaped formation, 41 miles in diameter, S. of
Albategnius, with a very discontinuous margin, interrupted on every side
by gaps and depressions, large and small; the most considerable of which
is the regular ring-plain Parrot _a_, on the E. An especially fine
valley, shown by Schmidt to consist in part of large inosculating
craters, cuts through the wall on the S.W., and runs on the E. side of
Argelander towards Airy. The floor of Parrot is very rugged.
DESCARTES.--This object, about 30 miles in diameter, situated N.W. of
Abulfeda, is bounded by ill-defined, broken, and comparatively low walls;
interrupted on the S.E. by a fine crater, Descartes A, and on the S.W. by
another, smaller. There is also a brilliant crater outside on the N.W.
Schmidt shows a crater-row on the floor, which I have seen as a cleft.
DOLLOND.--A bright crater, about 6 miles in diameter, on the N.E. side of
Descartes. Between it and the latter there is a rill-valley.
TACITUS.--A bright ring-plain, about 28 miles in diameter, a few miles E.
of Catherina, with a lofty wall rising both on the E. and W. to more than
11,000 feet above the floor. Its continuity is broken on the N. by a gap
occupied by a depression, and there is a conspicuous crater below the
crest on the S.W. The central mountain is connected with the N. wall by a
ridge, recalling the same arrangement within Madler. A range of lofty
hills, an offshoot of the Altai range, extends from Tacitus towards
Fermat.
ALMANON.--This ring-plain, with its companion Abulfeda on the N.E., is a
very interesting telescopic object. It is about 36 miles in diameter, and
is surrounded by an irregular border of polygonal shape, the greatest
altitude of which is about 6000 feet above the floor on the W. It is
slightly terraced, and is broken on the S. by a deep crater pertaining to
the bright and large formation Tacitus _b_, the E. border of which casts
a fine double-peaked shadow at sunrise. On the N.W. there is another
bright crater, the largest of the row, running in a W.S.W. direction, and
forming a W. extension of the remarkable crater-chain tangential to the
borders of Almanon and Abulfeda. The only objects on the floor are three
little hills, in a line, near the centre, a winding ridge on the W. side
of it, and two or three other low elevations.
ABULFEDA.--A larger and more massive formation than Almanon, 39 miles in
diameter, the E. wall rising about 10,000 feet above the interior, which
is depressed more than 3000 feet. It is continuous on the W., but much
broken by transverse valleys on the S.E., and by little depressions on
the N. On the S.E. originates the very curious bright crater-row which
runs in a straight line to the N.W. wall of Almanon, crossing for the
first few miles the lofty table-land lying on the S.E. side of the
border. With the exception of a low central mountain, the interior of
Abulfeda contains no visible detail. The rampart is finely terraced on
the E. and W. The E. _glacis_ is very rugged.
ARGELANDER.--This conspicuous ring-plain, about 20 miles in diameter, is,
if we except two smaller inosculating rings on the S.W. flank of
Albategnius, the most northerly of a remarkable serpentine chain of seven
moderately-sized formations, extending for nearly 180 miles from the S.W.
of Parrot to the N. side of Blanchinus. Its border is lofty, slightly
terraced within, and includes a central peak.
AIRY.--About 22 miles in diameter, connected with Argelander by a
depression bounded by linear walls. Its border, double on the S.E., is
broken on the S. by a prominent crater, with a smaller companion on the
W. of it; and again on the N.E. by another not so conspicuous. It has a
central peak. The next link in the chain of ring-plains is Airy _c_, a
very irregular object, somewhat larger, and with, for the most part,
linear walls.
DONATI.--A ring-plain on the S. of Airy _c_, about 22 miles in greatest
length. It is very irregular in outline, with a lofty broken border,
especially on the N. and S., where there are wide gaps. There is another
ring on the S.E.
FAYE.--The direction of the chain swerves considerably towards the E. at
this formation, which resembles Donati both in size and in irregularity
of outline. The wall, where it is not broken, is slightly terraced. There
is a craterlet on the S. rim and a central crater in the interior.
DELAUNAY.--Adjoins Faye on the S.E., and is a larger and more complex
object, of irregular form, with very lofty peaks on its border. A
prominent ridge of great height traverses the formation from N. to S.,
abutting on the W. border of Lacaille. Delaunay is the last link in the
chain commencing with Argelander.
LACAILLE.--An oblong enclosure situated on the N. side of Blanchinus, and
apparently about 30 miles in greatest diameter. The border is to a great
extent linear and continuous on the N., but elsewhere abounds in
depressions. Two large inosculating ring-plains are associated with the
N.E. wall.
BLANCHINUS.--A large walled-plain on the W. of Purbach and abutting on
the S. side of Lacaille. It much resembles Purbach in shape, but has
lower walls. Schmidt shows a crater on the N. side of the floor, which I
have seen, and a number of parallel ridges which have not been noted,
probably because they are only visible under very oblique light.
GEBER.--A bright ring-plain, 25 miles in diameter, S. of Almanon, with a
regular border, rising to a height on the W. of nearly 9000 feet above
the floor. There is a small crater on the crest of the S. wall, and
another on the N. A ring-plain about 8 miles in diameter adjoins the
formation on the N.E. According to Neison, there is a feeble central
hill, which, however, is not shown by Schmidt.
SACROBOSCO.--This is one of those extremely abnormal formations which are
almost peculiar to certain regions in the fourth quadrant. It is about 50
miles in greatest diameter, and is enclosed by a rampart of unequal
height, rising on the E. to 12,000 feet above the floor, but sinking in
places to a very moderate altitude. On the N. its contour is, if
possible, rendered still more irregular by the intrusion of a smaller
ring-plain. On the N.E. side of the floor stands a very bright little
crater and two others on the S. of the centre, each with central
mountains.
FERMAT.--An irregular ring-plain 25 miles in diameter on the W. of
Sacrobosco. Its partially terraced wall is broken on the N. by a gap
which communicates with the interior of a smaller formation. There are
some low hills on the floor, which is depressed 6000 feet below the crest
of the border.
AZOPHI.--A prominent ring-plain, 30 miles in diameter, E.N.E. of
Sacrobosco, its lofty barrier towering nearly 11,000 feet above a
somewhat dusky interior, which includes some light spots. A massive
curved mountain arm runs from the S. side of this formation to a small
ring-plain W. of Playfair.
ABENEZRA.--When observed near the morning terminator, this noteworthy
ring-plain, 27 miles in diameter, seems to be divided into two by a
curved ridge which traverses the formation from N. to S., and extends
beyond its limits. The irregular border rises on the W. to a height of
more than 14,000 feet above the deeply-sunken floor, which includes
several craters, hills, and ridges.
APIANUS.--A magnificent ring-plain, 38 miles in diameter, N.W. of
Aliacensis, with lofty terraced walls, rising on the N.E. to about 9000
feet above the interior, and crowned on the W. by three large conspicuous
craters. The border is broken on the N. by a smaller depression and a
large ring with low walls. The dark-grey floor appears to be devoid of
conspicuous detail.
PLAYFAIR.--A ring-plain, 28 miles in diameter, with massive walls. It is
situated on the N. of Apianus, and is connected with it by a mountain
arm. The rampart is tolerably continuous, but varies considerably in
altitude, rising on the S. to a height of more than 8000 feet above the
interior. On the E., extending towards Blanchinus, is a magnificent
unnamed formation, bounded on the E. by a broad lofty rampart flanking
Blanchinus, Lacaille, Delaunay, and Faye; and on the W. by Playfair and
the mountain arm just mentioned. It is fully 60 miles in length from N.
to S. Sunrise on this region affords a fine spectacle to the observer
with a large telescope. The best phase is when the morning terminator
intersects Aliacensis, as at this time the long jagged shadows of the E.
wall of Playfair and of the mountain arm are very prominent on the
smooth, greyish-blue surface of this immense enclosure.
PONTANUS.--An irregular ring-plain, 28 miles in diameter, S.S.W. of
Azophi, with a low broken border, interrupted on the S.W. by a smaller
ring-plain, which forms one of a group extending towards the S.W. The
dark floor includes a central mountain.
ALIACENSIS.--This ring-plain, 53 miles in diameter, with its neighbour
Werner on the N.E., are beautiful telescopic objects under a low sun. Its
lofty terraced border rises at one peak on the E. to the tremendous
height of 16,500 feet, and at another on the opposite side to nearly
12,000 feet above the floor. The wall on the S. is broken by a crater,
and on the W. traversed by narrow passes. There is also a prominent
crater on the inner slope of the N.E. wall. The floor includes a small
mountain, several little hills, and a crater.
WERNER.--A ring-plain, 45 miles in diameter, with a massive rampart
crowned by peaks almost as lofty as any on that of Aliacensis, and with
terraces fully as conspicuous. It has a magnificent central mountain,
4500 feet high. At the foot of the N.E. wall Madler observed a small
area, which he describes as rivalling the central peak of Aristarchus in
brilliancy. Webb, however, was unable to confirm this estimate, though he
noted it as very bright, and saw a minute black pit and narrow ravine
within it. Neison subsequently found that the black pit is a crater-cone.
It would perhaps be rash, with our limited knowledge of minute lunar
detail, to assert that Madler over-estimated the brightness of this area,
which may have been due to a _recent_ deposit round the orifice of the
crater-cone.
POISSON.--An irregular formation on the W. of Aliacensis, extending about
50 miles from W. to E., but much less in a meridional direction. Its N.
limits are marked by a number of overlapping ring-plains and craters, and
it is much broken elsewhere by smaller depressions. The E. wall is about
7000 feet in height.
GEMMA FRISIUS.--A great composite walled-plain, 80 miles or more in
length from N. to S., with a wall rising at one place nearly 14,000 feet
above the floor. It is broken on the N. by two fine ring-plains, each
about 20 miles in diameter, and on the E. by a third open to the E. There
is a central mountain, and several small craters on the floor, especially
on the W. side.
BUSCHING.--A ring-plain S. of Zagut, about 36 miles in diameter, with a
moderately high but irregular wall. There are several craterlets within
and some low hills.
BUCH.--Adjoins Busching on the S.E. It is about 31 miles in diameter, and
has a less broken barrier. There is a large crater on the E. wall, and
another smaller one on the S.W. Schmidt shows nothing on the floor, but
Neison noted two minute crater-cones.
MAUROLYCUS.--This unquestionably ranks as one of the grandest walled-
plains on the moon's visible surface, and when viewed under a low sun
presents a spectacle which is not easily effaced from the mind. Like so
many of the great enclosures in the fourth quadrant, it impresses one
with the notion that we have here the result of the crowding together of
a number of large rings which, when they were in a semi-fluid or viscous
condition, mutually deformed each other. It extends fully 150 miles from
E. to W., and more from N. to S.; so it may be taken to include an area
on the lunar globe which is, roughly speaking, equal to half the
superficies of Ireland. This vast space, bounded by one of the loftiest,
most massive, and prominently-terraced ramparts, includes ring-plains,
craters, crater-rows, and valleys,--in short, almost every type of lunar
formation. It towers on the E. to a height of nearly 14,000 feet above
the interior, and on the W., according to Schmidt, to a still greater
altitude. A fine rill-valley curves round the outer slope of the W. wall,
just below its crest, which is an easy object in a 8 1/2 inch reflector
when the opposite border is on the morning terminator, and could
doubtless be seen in a smaller instrument; and there is an especially
brilliant crater on the S. border, which is not visible till a somewhat
later stage of sunrise. The central mountain is of great altitude, its
loftiest peaks standing out amid the shadow long before a ray of sunlight
has reached the lower slopes of the walls. It is associated with a number
of smaller elevations. I have seen three considerable craters and several
smaller ones in the interior.
BAROCIUS.--A massive formation, about 50 miles in diameter, on the S.W.
side of Maurolycus, whose border it overlaps and considerably deforms.
Its wall rises on the E. to a height of 12,000 feet above the floor, and
is broken on the N.W. by two great ring-plains. On the inner slope of the
S.E. border is a curious oblong enclosure. There is nothing remarkable in
the interior. On the dusky grey plain W. of Maurolycus and Barocius there
is a number of little formations, many of them being of a very abnormal
shape, which are well worthy of examination. I have seen two short
unrecorded clefts in connection with these objects.
STOFLER.--A grand object, very similar in size and general character to
Maurolycus, its neighbour on the W. To view it and its surroundings at
the most striking phase, it should be observed when the morning
terminator lies a little E. of the W. wall. At this time the jagged,
clean-cut, shadows of the peaks on Faraday and the W. border, the fine
terraces, depressions, and other features on the illuminated section of
the gigantic rampart, and the smooth bluish-grey floor, combine to make a
most beautiful telescopic picture. At a peak on the N.E., the wall
attains a height of nearly 12,000 feet, but sinks to a little more than a
third of this height on the E. It is apparently loftiest on the N. The
most conspicuous of the many craters upon it is the bright deep circular
depression E. on the S. wall, and another, rather larger and less
regular, on the N.W., which has a very low rim on the side facing the
floor, and a craterlet on either side of the apparent gap. A large
lozenge-shaped enclosure abuts on the wall, near the crater E., with a
border crowned by a number of little peaks, which at an early stage of
sunrise resemble a chaplet of pearls. The floor of Stofler is apparently
very level, and in colour recalls the beautiful steel-grey tone of Plato
seen under certain conditions. I have noted several distinct little
craters on its surface, mostly on the N.E. side; and on the E. side a
triangular dark patch, close to the foot of the wall, very similar in
size and appearance to those within Alphonsus.
FARADAY.--A large ring-plain, about 35 miles in diameter, overlapping the
S.W. border of Stofler; its own rampart being overlapped in its turn by
two smaller ring-plains on the S.E., and by two still smaller formations
(one of which is square-shaped) on the N.W. The wall is broad and very
massive on the E. and N.E., prominently terraced, and includes many
brilliant little craters. Schmidt shows a ridge and several craters in
the interior.
LICETUS.--An irregular formation, about 50 miles in maximum width, on the
S. of Stofler, with the flanks of which it is connected by a coarse
valley. Neison points out that it consists of a group of ring-plains
united into one, owing to the separating walls having been partially
destroyed. This seems to be clearly the case, if Licetus is examined
under a low sun. On the E. side of the N. portion of the formation, the
wall rises to nearly 13,000 feet.
FERNELIUS.--A ring-plain, about 30 miles in diameter, abutting on the N.
wall of Stofler. It is overlapped on the E. by another similar formation
of about half its size. There are many craters and depressions on the
borders of both, and a large crater between the smaller enclosure and the
N.E. outer slope of Stofler. Schmidt shows eight craters on the floor of
Fernelius.
NONIUS.--A ring-plain, about 20 miles in diameter, abutting on the N.
wall of Fernelius. There is a prominent bright crater on the W. of it,
and another on the N., from which a delicate valley runs towards the W.
side of Walter.
CLAIRAUT.--A very peculiar formation, about 40 miles in diameter, S. of
Maurolycus, affording another good example of interference and
overlapping. The continuity of its border, nowhere very regular, has been
entirely destroyed on the S. by the subsequent formation of two large
rings, some 10 or 12 miles in diameter, the more easterly of which has,
in its turn, been partially wrecked on the N. by a smaller object of the
same class. There is also a ring-plain N.E. of Clairaut, which has very
clearly modified the shape of the border on this side. Two craters on the
floor of Clairaut are easy objects.
BACON.--A very fine ring-plain, 40 miles in diameter, S.W. of Clairaut.
At one peak on the E. the terraced wall rises to nearly 14,000 feet above
the interior. It is broken on the S. by three or four craters. On the W.
there is an irregular inconspicuous enclosure, whose contiguity has
apparently modified the shape of the border. There are two large rings on
the N. (the more easterly having a central peak), and a third on the E.
The floor appears to be devoid of prominent detail.
CUVIER.--A walled-plain, about 50 miles in diameter, on the S.E. of
Clairaut. The border on the E. rises to 12,000 feet; and on the N.W. is
much broken by depressions. Neison has seen a mound, with a minute crater
W. of it, on the otherwise undisturbed interior.
JACOBI.--A ring-plain S. of Cuvier, about 40 miles in diameter, with
walls much broken on the N. and S., but rising on the E. to nearly 10,000
feet. There is a group of craters (nearly central) on the floor. The
region S. of this formation abounds in large unnamed objects.
LILIUS.--An irregular ring-plain, 39 miles in diameter, with a rampart on
the E. nearly 10,000 feet above the floor. A smaller ring between it and
Jacobi has considerably inflected the wall towards the interior. It has a
conspicuous central mountain.
ZACH.--A massive formation, 46 miles in diameter, on the S. of Lilius,
with prominently terraced walls, rising on the E. to 13,000 feet above
the interior. A small ring-plain, whose wall stands 6000 feet above the
floor, is associated with the N. border. Two other rings, on the S.W. and
N.E. respectively, have craters on their ramparts and central hills.
PENTLAND.--A fine conspicuous formation under a low sun, even in a region
abounding in such objects. It is about 50 miles in diameter, with a
border exceeding in places 10,000 feet in height above the floor, which
includes an especially fine central mountain.
KINAU.--One of the group of remarkable ring-plains extending in a N.W.
direction from Pentland.
SIMPELIUS.--Another grand circumvallation, almost as large as Pentland,
but unfortunately much foreshortened. One of its peaks on the E. rises to
a height of more than 12,000 feet above the floor, on which there is a
small central mountain. Between Simpelius and Pentland are several ring-
plains, most of which appear to have been squeezed and deformed into
abnormal shapes.
CURTIUS.--A magnificent formation, about 50 miles in diameter, with one
of the loftiest ramparts on the visible surface, rising at a mountain
mass on the N.E. to more than 22,000 feet, an altitude which is only
surpassed by peaks on the walls of Newton and Casatus. There is a bright
crater on the S.E. border and another on the W. The formation is too near
the S. limb for satisfactory scrutiny. Between Curtius and Zach is a fine
group of unnamed enclosures.
APPENDIX
DESCRIPTION OF THE MAP
The accompanying map, eighteen inches in diameter, represents the moon
under mean libration. Meridian lines and parallels of latitude are drawn
at every 10 deg., except in the case of the meridians of 80 deg. E. and
W. longitude, which are omitted to avoid confusion, and as being
practically needless. These lines will enable the observer, with the aid
of the Tables in the Appendix, to find the position of the terminator at
any time required. As astronomical telescopes exhibit objects inverted,
maps of the moon are always drawn upside down, and with the right and
left interchanged, as in the diagram above, which also shows how the
quadrants are numbered.
This circle [drawing of circle], intended to be .15708 in diameter,
represents a circle of one degree in diameter at the centre of the map,
and as the length of one selenographical degree is 18.871 miles, it
represents an area of nearly 280 square miles.
The catalogue is so arranged that, beginning with the W. limb, and
referring to the lists under the first and fourth, and the second and
third quadrants, all the formations falling within the meridians 90 deg.
to 60 deg., 60 deg. to 40 deg., 40 deg. to 20 deg., 20 deg. to 0 deg.
(the central meridian), and from 0 deg. to 20 deg., and so on, to the E.
limb, will be found in convenient proximity in the text.
In the Catalogue, N. S. E. W. are used as abbreviations for the cardinal
points.
LIST OF THE MARIA, OR GREY PLAINS, TERMED "SEAS," &c.
FIRST QUADRANT.
Mare Tranquilitatis (nearly the whole), page 5.
,, Foecunditatis (the N. portion), 5.
,, Serenitatis, 5.
,, Crisium, 6.
,, Frigoris (a portion), 5.
,, Vaporum (nearly the whole), 6.
,, Humboldtianum, 6.
,, Smythii (a portion), 39.
Lacus Mortis, 53.
,, Somniorum.
Palus Somnii.
,, Nebularum (a portion), 62.
,, Putredinis, 61.
Sinus Medii (a portion), 6.
SECOND QUADRANT.
Mare Imbrium, 5.
,, Nubium (the N. portion), 5.
,, Frigoris (a portion), 5.
,, Vaporum (a portion), 6.
Oceanus Procellarum (the N. portion), 5.
Palus Nebularum (a portion), 62.
Sinus Iridum, 80.
,, Medii (a portion), 6.
,, Roris, 90.
,, Aestuum.
THIRD QUADRANT.
Mare Nubium (the greater portion), 5.
,, Humorum, 6.
Oceanus Procellarum (the S. portion), 5.
Sinus Medii (a small portion), 6.
FOURTH QUADRANT.
Mare Foecunditatis (the greater portion), 5.
,, Nectaris, 7.
,, Tranquilitatis (a small portion), 5.
,, Australe, 127.
,, Smythii (a portion), 39.
Sinus Medii (a portion), 6.
LIST OF SOME OF THE MOST PROMINENT MOUNTAIN RANGES, PROMONTORIES,
ISOLATED MOUNTAINS, AND REMARKABLE HILLS.
FIRST QUADRANT.
The Alps. The western portion of the range.
The Apennines. The extreme northern part of the range.
The Caucasus.
The Haemus.
The Taurus.
The North Polar Range. On the limb extending from N. lat. 81 deg.
towards the E.
The Humboldt Mountains. On the limb from N. lat. 72 deg. to N. lat. 53
deg.
Mount Argaeus. A mountain mass rising some 8000 feet above the Mare
Serenitatis in N. lat. 20 deg., W. long. 28 deg., N.W. of Dawes.
Prom. Acherusia. A bright promontory at the W. extremity of the Haemus
range, rising nearly 5000 feet above the Mare Serenitatis. N. lat. 17
deg., W. long. 22 deg.
Cape Agarum. The N. end of a projecting headland on the S.W. side of the
Mare Crisium, in N. lat. 14 deg., W. long. 66 deg., rising nearly 11,000
feet above the Mare.
Le Monnier A. An isolated mountain more than 3000 feet high, standing
about midway between the extremities of the bay: probably a relic of a
once complete ring.
Secchi. South of this formation there is a lofty prominent isolated
mountain.
Manilius A and beta. Two conspicuous mountains N. of Manilius; A,
the more westerly, being more than 5000 feet, and beta about 2000
feet in height.
Autolycus A. A mountain of considerable altitude, S. of this formation.
Mont Blanc. Principal peak, N. lat. 46 deg., W. long. 0 deg. 30 min.,
nearly 12,000 feet in height.
Cassini epsilon and delta. Two adjoining mountain masses N. of Cassini,
more than 5000 feet high.
Eudoxus. S.E. of this formation, in N. lat. 43 deg., W. long. 10 deg.,
are two bright mountain masses, the more southerly rising 7000, and the
other 4000 feet above the surface.
Mount Hadley. The northern extremity of the Apennines, in N. lat. 27 deg.
W. long. 5 deg., rising more than 15,000 feet above the Mare.
Mount Bradley. A promontory of the Apennines, in N, lat. 23 deg., W.
long. 1 deg., nearly 14,000 feet above the Mare Imbrium.
The Silberschlag Range, running from near the S.E. side of Julius Caesar
to the region W. of Agrippa.
SECOND QUADRANT.
The Alps. The eastern and greater portion.
The Apennines. Nearly the whole of the range.
The Carpathians.
The Teneriffe Mountains. S.E. of Plato. Highest peak, 8000 feet.
The Straight Range. East of the last, in N. lat. 48 deg., E. long. 20
deg.
The Harbinger Mountains. N.W. of Aristarchus.
The Hercynian Mountains. Near the N.E. limb, E. of Otto Struve, N. lat.
25 deg.
Mount Huygens. A mountain mass projecting from the escarpment of the
Apennines, in N. lat. 20 deg., E. long. 3 deg., one peak rising to 18,000
feet above the Mare Imbrium.
Mount Wolf. A great square-shaped mountain mass, near the S.E.
extremity of the Apennines, in N. lat. 17 deg., E. long. 9 deg., the
loftiest peak rising to nearly 12,000 feet above the Mare Imbrium.
Eratosthenes I and X. Two isolated mountains N. of this formation, in N.
lat. 20 deg.; X is 1800 feet in height.
Pico. A magnificent isolated mountain, S. of Plato, in N. lat. 45 deg.,
E. long. 9 deg., rising some 8000 feet above the Mare Imbrium.
Pico B. A triple-peaked mountain a few miles S. of Pico.
Piton. A bright isolated mountain 7000 feet high, in N. lat. 1 deg., E.
long. 1 deg.
Fontinelle A. A conspicuous isolated mountain about 3000 feet high, S. of
Fontinelle.
Archimedes Z. A triangular-shaped group E. of Archimedes, in N. lat. 31
deg., E. long. 8 deg., the highest of the peaks rising more than 2000
feet.
Caroline Herschel. E. of this formation is a double-peaked mountain
rising to 1300 feet.
Gruithuisen delta and gamma. On the N. of this bright crater, in N. lat.
36 deg., E. long. 40 deg., rises a fine mountain, delta, nearly 6000 feet
in height, and on the N.E. of it the larger mass gamma, almost as lofty.
Mairan. There is a group of three bright little mountains, the loftiest
about 800 feet above the Mare, some distance E. of this formation.
Euler beta. A fine but small mountain group, more than 3600 feet high, on
the Mare Imbrium, S.E. of Euler.
The Laplace Promontory. A magnificent headland on the N. side of the
Sinus Iridum, rising about 9000 feet above the latter, and about 7000
feet above the Mare Imbrium.
Cape Heraclides. A fine but less prominent headland on the opposite side
of the bay, rising more than 4000 feet above it.
Lahire. A large bright isolated mountain in the Mare Imbrium, N.E. of
Lambert, in N. lat. 27 deg., E. long. 25 deg. It is, according to
Schroter, nearly 5000 feet high.
Delisle beta. A curious club-shaped mountain on the S.E. of this
formation, nearly 4000 feet in height.
Pytheas beta. An isolated mountain, 900 feet high, in N. lat. 20 deg., E.
long. 23 deg.
Kirch. There is a small isolated hill a few miles N. of this formation.
Kirch GAMMA. A bright mountain about 700 feet high, in N. lat. 39 deg.,
E. long. 3 deg.
Piazzi Smyth beta. A small bright isolated mountain on a ridge S. of
this, is a noteworthy object under a low sun.
Lambert GAMMA. In N. lat. 26 deg., E. long. 18 deg.; a remarkable curved
mountain about 3000 feet in height, a brilliant object under a low sun.
D'Alembert Mountains. A range on the E. limb running S. from N. lat. 12
deg.
Wollaston. An isolated triangular mountain about midway between this and
Wollaston B.
THIRD QUADRANT.
The Riphaean Mountains. An isolated range S. of Landsberg in S. lat. 7
deg., E. long. 28 deg. They run in a meridional direction, and rise at
one peak to nearly 3000 feet above the Oceanus Procellarum.
The Percy Mountains extend from the eastern flank of Gassendi
towards Mersenius, forming the north-eastern border of the Mare
Humorum.
Prom. Aenarium. A steep bluff situated at the northern end of
a plateau, some distance E. of Arzachel, in S. lat. 18 deg., E. long. 9
deg. It rises some 2000 feet above the Mare Nubium.
Euclides zeta and chi. Two mountain masses N. of this formation in S.
lat. 5 deg.; zeta rises about 1700 feet above the Mare; both are
evidently offshoots from the Riphaean range.
Landsberg H. An isolated hill in S. lat. 4 deg., E. long. 25 deg.
Nicollet C. S.E. of Nicollet, in S. lat. 22 deg., E. long. 17 deg.; is
hemmed in by a mountain mass rising to more than 2000 feet above the Mare
Nubium.
The Stag's-Horn Mountains. At the S. end of the straight wall, or
"railroad," in S. lat. 24 deg., E. long. 8 deg., a curious mountain mass
rising about 2000 feet above the Mare Nubium.
Lacroix delta. A mountain more than 7000 feet high, N. of Lacroix.
Flamsteed E. A mountain of more than 3000 feet in S. lat. 4 deg., E.
long. 51 deg.
D'Alembert Mountains. A very lofty range on the E. limb, extending to S.
lat. 11 deg.
The Cordilleras. Close to the E. limb; they lie between S. lat. 8 deg.
and S. lat. 23 deg.
Rook Mountains. On the E. limb, extending from about S. lat. 18 deg. to
S. lat. 35 deg. According to Schroter, they attain a height of 25,000
feet.
Dorfel Mountains. On the S.E. limb between S. lat. 57 deg. and S. lat. 80
deg.
Leibnitz Mountains. On the S. limb extending W. from S. lat. 80 deg.
beyond the Pole on to the Fourth Quadrant. Perhaps the loftiest range on
the limb. Madler's measures give more than 27,000 feet as the height of
one peak, and there are several others nearly as high.
FOURTH QUADRANT.
The Altai Mountains. A fine conspicuous serpentine range, extending from
the E. side of Piccolomini in a north-easterly direction to the region
between Tacitus and Catherina, a length of about 275 miles. The loftiest
peak is over 13,000 feet. The average height of the southern portion is
about 6000 feet. The region lying on the S.E. of this range is a vast
tableland, devoid of prominent objects, rising gradually towards the
mountains, which shelve rapidly down to an equally barren expanse on the
N.W.
The Pyrenees. These mountains, on the E. of Guttemberg, border the
western side of the Mare Nectaris. Their loftiest peak, rising nearly to
12,000 feet, is on the S.E. of Guttemberg.
LIST OF THE PRINCIPAL RAY-SYSTEMS, LIGHT-SURROUNDED CRATERS, AND LIGHT-
SPOTS.
[In this list, which does claim to be exhaustive, most of the objects
noted by Schmidt are incorporated.]
FIRST QUADRANT.
Autolycus. Encircled by a delicate nimbus, throwing out four or five
prominent rays extending towards Archimedes. Seen best under evening
illumination.
Aristillus. The centre of a noteworthy system of delicate rays extending
W. towards the Caucasus; and on the S. disappearing among the rays of
Autolycus. They are traceable on the Mare Nubium near Kirch.
Theaetetus. A very brilliant group of little hills E. of this formation.
Eudoxus A. A light-surrounded crater W. of Eudoxus, with distinct long
streaks, one of which extends to the S. wall of Aristoteles.
Aristoteles A. A light-surrounded crater in the Mare Frigoris, N.E. of
Aristoteles.
Aratus. A very conspicuously brilliant crater in the Apennines, with a
smaller light-surrounded crater W. of it.
Sulpicius Gallus. A light spot near.
Manilius. Surrounded by a light halo and streaks.
Taquet. Has a prominent nimbus, and indications of very delicate streaks.
Plinius A. Is surrounded by a well-marked halo.
Posidonius gamma. Among the hills E. of this formation a light spot
resembling Linne, according to Schmidt. He first saw it in 1867, when it
had a delicate black spot in the centre. Dr. Vogel observed and drew it
in 1871 with the great refractor at Bothkamp. These observations were
confirmed by Schmidt in 1875 with the 14-feet refractor at Berlin.
Littrow. A very bright light-spot with streaks, on the site of a little
crater and well-known cleft E. of this ring-plain.
Romer. A light-surrounded mountain on the E.
Macrobius. Two light-surrounded craters on the E. of this formation, the
more northerly being the brighter.
Cleomedes A. (On the floor.) Surrounded by a nimbus and rays. Large
crater, A, on the E. has also a nimbus and rays.
Agrippa. Exhibits faint rays.
Godin. Exhibits faint rays.
Proclus. A well-known ray-centre, some of the rays prominent on part of
the Mare Crisium.
Taruntius. Has a very faint nimbus, with rays, on a dark surface.
Dionysius. A brilliant crater with a prominent, bright, excentrically
placed nimbus on a dark surface, on which distinct rays are displayed.
Hypatia B. A very small bright crater on a dark surface: surrounded by a
faint nimbus.
Apollonius. Among the hills S. of this, there is a small bright streak
system.
Eimmart. There is a large white spot N.W. of this.
Geminus is associated with a system of very delicate rays.
Menelaus. A brilliant object. It is traversed by a long ray from Tycho.
SECOND QUADRANT.
Anaxagoras. The centre of an important ray-system.
Timocharis is surrounded by a pale irregular nimbus and faint rays, most
prominently developed on the W. side of the formation.
Copernicus. Next to Tycho, the most extended ray-centre on the visible
surface. Some distance on the E., in E. long. 25 deg., N. lat. 11 deg.,
lies a very small but conspicuous system, and in E. long. 22 deg., N.
lat. 8 deg. a bright light spot among little hills.
Gambart A. A bright crater with large nimbus and rays.
Landsberg A. A light-surrounded crater on a dark surface, with
companions, referred to under the Third Quadrant.
Encke. There is a light-surrounded crater S. of this.
Kepler. A noted ray-centre. It is surrounded by an extensive halo,
especially well developed on the E., across the Mare Procellarum.
Bessarion. Two bright craters: the more northerly is prominently
light-surrounded, while its companion is less conspicuously so.
Aristarchus.--The most conspicuous bright centre on the moon, the
origin of a complicated ray-system.
Delisle. S. of this formation there is a tolerably bright spot on the
site of some hills.
Timaeus. A ray-centre.
Euler. Feeble halo with streaks.
Galileo. Between this and Reiner is a curious bright formation with short
rays, referred to in the Catalogue, under Reiner.
Cavalerius. A light streak originating in the W. wall, and extending on
to the Oceanus Procellarum.
Olbers. A considerable ray-system, but seldom distinctly visible.
Lichtenberg. Faintly light-surrounded.
THIRD QUADRANT.
Tycho. The largest and best known system on the visible surface.
Zuchius. A remarkable ray-system, but one which is only well seen when
libration is favourable.
Bailly. N. of the centre of this great enclosure are two very distinct
radiating streaks.
Schickard. Four conspicuous light spots, probably craters, on the S.E.
Byrgius A. A brilliant ray-centre, most of the rays trending eastward
from a nimbus.
Hainzel. There are several bright spots E. of this formation.
Mersenius. Two or three light-rays originate from a point on the W.
rampart.
Mersenius C. A light-surrounded crater with short rays.
Grimaldi. There are three bright spots on the W. wall.
Damoiseau. A light-surrounded crater W. of Damoiseau, E. long. 58 deg.,
S. lat. 6 deg.
Flamsteed C. A light-surrounded crater on a dark surface.
Lubieniezky A. Crater with halo on a dark surface.
Lubieniezky F. Crater with halo on a dark surface.
Lubieniezky G. Crater with halo on a dark surface.
Birt _a_. A light-surrounded crater.
Landsberg. E. of Landsberg, four light-surrounded craters, forming
with Landsberg A (in the Second Quadrant) an interesting group.
Lohrmann A. A light-surrounded crater, with a light area a few miles N.
of it. S. lat. 1 deg., E. long. 61 deg.
Euclides. Has a conspicuous nimbus with traces of rays, a typical
example.
Guerike. There is a crater, with nimbus, W. of this, in E. long. 12 deg.,
S. lat. 11 deg. 5 min.
Parry. A very brilliant light-spot in the S. wall.
Parry A. Surrounded by a bright nimbus.
Alpetragius B. A conspicuous light-surrounded crater, one of the most
remarkable on the moon.
Alpetragius _d_ (E. long. 11 deg., S. lat. 13 deg. 8 min.). A bright
spot, seen by Madler as a crater, but which, as Schmidt found in 1868, no
longer answers to this description.
Mosting C. A light-surrounded crater.
Lalande. Has a large nimbus and distinct rays.
Hell. A large ill-defined spot in E. long. 4 deg., S. lat. 33 deg. This
is most probably the site of the white cloud seen by Cassini.
Mercator. There is a brilliant crater and light area under E. wall.
FOURTH QUADRANT.
Stevinus _a_. A crater E. of Stevinus; it is a centre of wide extending
rays.
Furnerius A. Prominently light-surrounded, with bright streaks,
radiating for a long distance N. and S.
Messier A. The well-known "Comet" rays, extending E. of this.
Langrenus. Has a large but very pale ray-system. It is best seen under a
low evening sun. Three long streaks radiate towards the E. from the foot
of the _glacis_ of the S.E. wall.
Censorinus. A very brilliant crater with faint rays.
Theophilus. The central mountain is faintly light-surrounded.
Madler. This ring-plain and the neighbourhood on the N. and N.W.,
include many bright areas and curious streaks.
Almanon. About midway between this and Argelander is a very brilliant
little crater.
Beaumont. Between this and Cyrillus stand three considerable craters
with nimbi.
Cyrillus A. A prominent light-surrounded crater.
Alfraganus. A light-surrounded crater with rays.
POSITION OF THE LUNAR TERMINATOR
Though the position of the Lunar Terminator is given for mean midnight
throughout the year in that very useful publication the Companion to the
Observatory, it is frequently important in examining or comparing former
drawings and observations to ascertain its position at the times when
they were made. For this purpose the subjoined tables (which first
appeared in the Selenographical Journal) will be found useful, as they
give for any day between A.D. 1780 and A.D. 1900 the selenographical
longitude of the point where the terminator crosses the moon's equator,
which it does very nearly at right angles.
[Tables and examples]
LUNAR ELEMENTS
Moon's mean apparent diameter - 31 min. 8 sec.
Moon's maximum apparent diameter - 33 min. 33.20 sec.
Moon's minimum apparent diameter - 29 min. 23.65 sec.
Moon's diameter, in miles - 2163 miles.
Volume (earth's = 1) - 1/49.20 or 0.02033.
Mass (earth's = 1) - 1/81.40 or 0.0128.
Density (earth's = 1) - 0.60419, or 3.444 the density of water
(water being unity).
Surface area, about 14,600,000 square miles (earth's surface area,
196,870,000 miles)
Earth's surface area = 1, moon's - About 2/27 or 0.07407.
Action of gravity at surface - 0.16489 or 1/6.065 of the earth's.
Surface of moon never seen - 0.4100.
Surface of moon seen at one time or another - 0.5900.
Synodical revolution, or interval from new moon to new moon (commonly
called a lunation) - 29 d. 12 h. 44 m. 2.684 s. - 29.5305887 days.
Sidereal revolution, or time taken in passing from one star to the same
star again - 27 d. 7 h. 43 m. 11.545 s. - 27.3216614 days.
Tropical revolution, or time taken in passing from "the first point of
Aries" to the same point again - 27 d. 7 h. 43 m. 4.68 s. - 27.321582
days.
Anomalistic revolution, or time taken in passing from perigee to perigee
- 27 d. 13 h. 18 m. 37.44 s. - 27.55460 days.
Nodical revolution, or time taken in passing from rising node to rising
node - 27 d. 5h. 5m. 35.81 s. - 27.21222 days.
Distance (mean) in terms of the equatorial radius of the earth - 60.27.
Distance in miles (mean) - 238,840 miles.
Distance, maximum - 252,972 miles.
Distance, minimum - 221,614 miles.
Mean excentricity of moon's orbit - 0.05490807.
Inclination of moon's orbit to the ecliptic (mean) - 5 deg. 8 min. 39.96
sec.
Inclination of moon's axis to the ecliptic - 87 deg. 27 min. 51 sec.
Inclination of moon's equator to the ecliptic - 1 deg. 32 min. 9 sec.
Maximum libration in latitude - 6 deg. 44 min.
Maximum libration in longitude - 7 deg. 45 min.
Maximum total libration from earth's centre - 10 deg. 16 min.
Maximum diurnal libration - 1 deg. 1 min. 28.8 sec.
Angle subtended by one degree of selenographical latitude and longitude
at the centre of the moon's disc, when at its mean distance - 16.566 sec.
Length of a degree under these conditions - 18.871 miles.
Selenographical arc at the centre of the moon's surface, subtending an
angle of one second of arc - 3 min. 37.31 sec.
Miles at the centre of the moon's disc, subtending an angle of one second
of arc - 1.139
[It must be remembered that this value is _increased_, in departing from
the centre, in the proportion of the secants of the angular distance from
the centre.]
Period of similar phase - 59 d. 1h. 28m. = 2 lunations.
Or, more accurately - 442 d. 23 h. = 15 lunations.
End of the Project Gutenberg EBook of The Moon, by Thomas Gwyn Elger
*** END OF THIS PROJECT GUTENBERG EBOOK THE MOON ***
***** This file should be named 17712.txt or 17712.zip *****
This and all associated files of various formats will be found in:
http://www.gutenberg.org/1/7/7/1/17712/
Produced by Steve Ridgway
Updated editions will replace the previous one--the old editions
will be renamed.
Creating the works from public domain print editions means that no
one owns a United States copyright in these works, so the Foundation
(and you!) can copy and distribute it in the United States without
permission and without paying copyright royalties. Special rules,
set forth in the General Terms of Use part of this license, apply to
copying and distributing Project Gutenberg-tm electronic works to
protect the PROJECT GUTENBERG-tm concept and trademark. Project
Gutenberg is a registered trademark, and may not be used if you
charge for the eBooks, unless you receive specific permission. If you
do not charge anything for copies of this eBook, complying with the
rules is very easy. You may use this eBook for nearly any purpose
such as creation of derivative works, reports, performances and
research. They may be modified and printed and given away--you may do
practically ANYTHING with public domain eBooks. Redistribution is
subject to the trademark license, especially commercial
redistribution.
*** START: FULL LICENSE ***
THE FULL PROJECT GUTENBERG LICENSE
PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK
To protect the Project Gutenberg-tm mission of promoting the free
distribution of electronic works, by using or distributing this work
(or any other work associated in any way with the phrase "Project
Gutenberg"), you agree to comply with all the terms of the Full Project
Gutenberg-tm License (available with this file or online at
http://gutenberg.org/license).
Section 1. General Terms of Use and Redistributing Project Gutenberg-tm
electronic works
1.A. By reading or using any part of this Project Gutenberg-tm
electronic work, you indicate that you have read, understand, agree to
and accept all the terms of this license and intellectual property
(trademark/copyright) agreement. If you do not agree to abide by all
the terms of this agreement, you must cease using and return or destroy
all copies of Project Gutenberg-tm electronic works in your possession.
If you paid a fee for obtaining a copy of or access to a Project
Gutenberg-tm electronic work and you do not agree to be bound by the
terms of this agreement, you may obtain a refund from the person or
entity to whom you paid the fee as set forth in paragraph 1.E.8.
1.B. "Project Gutenberg" is a registered trademark. It may only be
used on or associated in any way with an electronic work by people who
agree to be bound by the terms of this agreement. There are a few
things that you can do with most Project Gutenberg-tm electronic works
even without complying with the full terms of this agreement. See
paragraph 1.C below. There are a lot of things you can do with Project
Gutenberg-tm electronic works if you follow the terms of this agreement
and help preserve free future access to Project Gutenberg-tm electronic
works. See paragraph 1.E below.
1.C. The Project Gutenberg Literary Archive Foundation ("the Foundation"
or PGLAF), owns a compilation copyright in the collection of Project
Gutenberg-tm electronic works. Nearly all the individual works in the
collection are in the public domain in the United States. If an
individual work is in the public domain in the United States and you are
located in the United States, we do not claim a right to prevent you from
copying, distributing, performing, displaying or creating derivative
works based on the work as long as all references to Project Gutenberg
are removed. Of course, we hope that you will support the Project
Gutenberg-tm mission of promoting free access to electronic works by
freely sharing Project Gutenberg-tm works in compliance with the terms of
this agreement for keeping the Project Gutenberg-tm name associated with
the work. You can easily comply with the terms of this agreement by
keeping this work in the same format with its attached full Project
Gutenberg-tm License when you share it without charge with others.
1.D. The copyright laws of the place where you are located also govern
what you can do with this work. Copyright laws in most countries are in
a constant state of change. If you are outside the United States, check
the laws of your country in addition to the terms of this agreement
before downloading, copying, displaying, performing, distributing or
creating derivative works based on this work or any other Project
Gutenberg-tm work. The Foundation makes no representations concerning
the copyright status of any work in any country outside the United
States.
1.E. Unless you have removed all references to Project Gutenberg:
1.E.1. The following sentence, with active links to, or other immediate
access to, the full Project Gutenberg-tm License must appear prominently
whenever any copy of a Project Gutenberg-tm work (any work on which the
phrase "Project Gutenberg" appears, or with which the phrase "Project
Gutenberg" is associated) is accessed, displayed, performed, viewed,
copied or distributed:
This eBook is for the use of anyone anywhere at no cost and with
almost no restrictions whatsoever. You may copy it, give it away or
re-use it under the terms of the Project Gutenberg License included
with this eBook or online at www.gutenberg.org
1.E.2. If an individual Project Gutenberg-tm electronic work is derived
from the public domain (does not contain a notice indicating that it is
posted with permission of the copyright holder), the work can be copied
and distributed to anyone in the United States without paying any fees
or charges. If you are redistributing or providing access to a work
with the phrase "Project Gutenberg" associated with or appearing on the
work, you must comply either with the requirements of paragraphs 1.E.1
through 1.E.7 or obtain permission for the use of the work and the
Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or
1.E.9.
1.E.3. If an individual Project Gutenberg-tm electronic work is posted
with the permission of the copyright holder, your use and distribution
must comply with both paragraphs 1.E.1 through 1.E.7 and any additional
terms imposed by the copyright holder. Additional terms will be linked
to the Project Gutenberg-tm License for all works posted with the
permission of the copyright holder found at the beginning of this work.
1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm
License terms from this work, or any files containing a part of this
work or any other work associated with Project Gutenberg-tm.
1.E.5. Do not copy, display, perform, distribute or redistribute this
electronic work, or any part of this electronic work, without
prominently displaying the sentence set forth in paragraph 1.E.1 with
active links or immediate access to the full terms of the Project
Gutenberg-tm License.
1.E.6. You may convert to and distribute this work in any binary,
compressed, marked up, nonproprietary or proprietary form, including any
word processing or hypertext form. However, if you provide access to or
distribute copies of a Project Gutenberg-tm work in a format other than
"Plain Vanilla ASCII" or other format used in the official version
posted on the official Project Gutenberg-tm web site (www.gutenberg.org),
you must, at no additional cost, fee or expense to the user, provide a
copy, a means of exporting a copy, or a means of obtaining a copy upon
request, of the work in its original "Plain Vanilla ASCII" or other
form. Any alternate format must include the full Project Gutenberg-tm
License as specified in paragraph 1.E.1.
1.E.7. Do not charge a fee for access to, viewing, displaying,
performing, copying or distributing any Project Gutenberg-tm works
unless you comply with paragraph 1.E.8 or 1.E.9.
1.E.8. You may charge a reasonable fee for copies of or providing
access to or distributing Project Gutenberg-tm electronic works provided
that
- You pay a royalty fee of 20% of the gross profits you derive from
the use of Project Gutenberg-tm works calculated using the method
you already use to calculate your applicable taxes. The fee is
owed to the owner of the Project Gutenberg-tm trademark, but he
has agreed to donate royalties under this paragraph to the
Project Gutenberg Literary Archive Foundation. Royalty payments
must be paid within 60 days following each date on which you
prepare (or are legally required to prepare) your periodic tax
returns. Royalty payments should be clearly marked as such and
sent to the Project Gutenberg Literary Archive Foundation at the
address specified in Section 4, "Information about donations to
the Project Gutenberg Literary Archive Foundation."
- You provide a full refund of any money paid by a user who notifies
you in writing (or by e-mail) within 30 days of receipt that s/he
does not agree to the terms of the full Project Gutenberg-tm
License. You must require such a user to return or
destroy all copies of the works possessed in a physical medium
and discontinue all use of and all access to other copies of
Project Gutenberg-tm works.
- You provide, in accordance with paragraph 1.F.3, a full refund of any
money paid for a work or a replacement copy, if a defect in the
electronic work is discovered and reported to you within 90 days
of receipt of the work.
- You comply with all other terms of this agreement for free
distribution of Project Gutenberg-tm works.
1.E.9. If you wish to charge a fee or distribute a Project Gutenberg-tm
electronic work or group of works on different terms than are set
forth in this agreement, you must obtain permission in writing from
both the Project Gutenberg Literary Archive Foundation and Michael
Hart, the owner of the Project Gutenberg-tm trademark. Contact the
Foundation as set forth in Section 3 below.
1.F.
1.F.1. Project Gutenberg volunteers and employees expend considerable
effort to identify, do copyright research on, transcribe and proofread
public domain works in creating the Project Gutenberg-tm
collection. Despite these efforts, Project Gutenberg-tm electronic
works, and the medium on which they may be stored, may contain
"Defects," such as, but not limited to, incomplete, inaccurate or
corrupt data, transcription errors, a copyright or other intellectual
property infringement, a defective or damaged disk or other medium, a
computer virus, or computer codes that damage or cannot be read by
your equipment.
1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right
of Replacement or Refund" described in paragraph 1.F.3, the Project
Gutenberg Literary Archive Foundation, the owner of the Project
Gutenberg-tm trademark, and any other party distributing a Project
Gutenberg-tm electronic work under this agreement, disclaim all
liability to you for damages, costs and expenses, including legal
fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT
LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE
PROVIDED IN PARAGRAPH F3. YOU AGREE THAT THE FOUNDATION, THE
TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE
LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR
INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH
DAMAGE.
1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a
defect in this electronic work within 90 days of receiving it, you can
receive a refund of the money (if any) you paid for it by sending a
written explanation to the person you received the work from. If you
received the work on a physical medium, you must return the medium with
your written explanation. The person or entity that provided you with
the defective work may elect to provide a replacement copy in lieu of a
refund. If you received the work electronically, the person or entity
providing it to you may choose to give you a second opportunity to
receive the work electronically in lieu of a refund. If the second copy
is also defective, you may demand a refund in writing without further
opportunities to fix the problem.
1.F.4. Except for the limited right of replacement or refund set forth
in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER
WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO
WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE.
1.F.5. Some states do not allow disclaimers of certain implied
warranties or the exclusion or limitation of certain types of damages.
If any disclaimer or limitation set forth in this agreement violates the
law of the state applicable to this agreement, the agreement shall be
interpreted to make the maximum disclaimer or limitation permitted by
the applicable state law. The invalidity or unenforceability of any
provision of this agreement shall not void the remaining provisions.
1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the
trademark owner, any agent or employee of the Foundation, anyone
providing copies of Project Gutenberg-tm electronic works in accordance
with this agreement, and any volunteers associated with the production,
promotion and distribution of Project Gutenberg-tm electronic works,
harmless from all liability, costs and expenses, including legal fees,
that arise directly or indirectly from any of the following which you do
or cause to occur: (a) distribution of this or any Project Gutenberg-tm
work, (b) alteration, modification, or additions or deletions to any
Project Gutenberg-tm work, and (c) any Defect you cause.
Section 2. Information about the Mission of Project Gutenberg-tm
Project Gutenberg-tm is synonymous with the free distribution of
electronic works in formats readable by the widest variety of computers
including obsolete, old, middle-aged and new computers. It exists
because of the efforts of hundreds of volunteers and donations from
people in all walks of life.
Volunteers and financial support to provide volunteers with the
assistance they need, is critical to reaching Project Gutenberg-tm's
goals and ensuring that the Project Gutenberg-tm collection will
remain freely available for generations to come. In 2001, the Project
Gutenberg Literary Archive Foundation was created to provide a secure
and permanent future for Project Gutenberg-tm and future generations.
To learn more about the Project Gutenberg Literary Archive Foundation
and how your efforts and donations can help, see Sections 3 and 4
and the Foundation web page at http://www.pglaf.org.
Section 3. Information about the Project Gutenberg Literary Archive
Foundation
The Project Gutenberg Literary Archive Foundation is a non profit
501(c)(3) educational corporation organized under the laws of the
state of Mississippi and granted tax exempt status by the Internal
Revenue Service. The Foundation's EIN or federal tax identification
number is 64-6221541. Its 501(c)(3) letter is posted at
http://pglaf.org/fundraising. Contributions to the Project Gutenberg
Literary Archive Foundation are tax deductible to the full extent
permitted by U.S. federal laws and your state's laws.
The Foundation's principal office is located at 4557 Melan Dr. S.
Fairbanks, AK, 99712., but its volunteers and employees are scattered
throughout numerous locations. Its business office is located at
809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email
[email protected]. Email contact links and up to date contact
information can be found at the Foundation's web site and official
page at http://pglaf.org
For additional contact information:
Dr. Gregory B. Newby
Chief Executive and Director
[email protected]
Section 4. Information about Donations to the Project Gutenberg
Literary Archive Foundation
Project Gutenberg-tm depends upon and cannot survive without wide
spread public support and donations to carry out its mission of
increasing the number of public domain and licensed works that can be
freely distributed in machine readable form accessible by the widest
array of equipment including outdated equipment. Many small donations
($1 to $5,000) are particularly important to maintaining tax exempt
status with the IRS.
The Foundation is committed to complying with the laws regulating
charities and charitable donations in all 50 states of the United
States. Compliance requirements are not uniform and it takes a
considerable effort, much paperwork and many fees to meet and keep up
with these requirements. We do not solicit donations in locations
where we have not received written confirmation of compliance. To
SEND DONATIONS or determine the status of compliance for any
particular state visit http://pglaf.org
While we cannot and do not solicit contributions from states where we
have not met the solicitation requirements, we know of no prohibition
against accepting unsolicited donations from donors in such states who
approach us with offers to donate.
International donations are gratefully accepted, but we cannot make
any statements concerning tax treatment of donations received from
outside the United States. U.S. laws alone swamp our small staff.
Please check the Project Gutenberg Web pages for current donation
methods and addresses. Donations are accepted in a number of other
ways including checks, online payments and credit card donations.
To donate, please visit: http://pglaf.org/donate
Section 5. General Information About Project Gutenberg-tm electronic
works.
Professor Michael S. Hart is the originator of the Project Gutenberg-tm
concept of a library of electronic works that could be freely shared
with anyone. For thirty years, he produced and distributed Project
Gutenberg-tm eBooks with only a loose network of volunteer support.
Project Gutenberg-tm eBooks are often created from several printed
editions, all of which are confirmed as Public Domain in the U.S.
unless a copyright notice is included. Thus, we do not necessarily
keep eBooks in compliance with any particular paper edition.
Most people start at our Web site which has the main PG search facility:
http://www.gutenberg.org
This Web site includes information about Project Gutenberg-tm,
including how to make donations to the Project Gutenberg Literary
Archive Foundation, how to help produce our new eBooks, and how to
subscribe to our email newsletter to hear about new eBooks.
