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.