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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..6833f05 --- /dev/null +++ b/.gitattributes @@ -0,0 +1,3 @@ +* text=auto +*.txt text +*.md text diff --git a/17712.txt b/17712.txt new file mode 100644 index 0000000..01fe343 --- /dev/null +++ b/17712.txt @@ -0,0 +1,7431 @@ +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 + +Character set encoding: ASCII + +*** 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. 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