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.