The Moon Part 11

WILSON.--The most southerly of the chain of five ma.s.sive ring-plains, extending in an almost unbroken line from Segner and differing only very slightly in size. It is about 40 miles in diameter, and has a somewhat irregular border, both as regards shape and height, rising at one peak on the S.W. to nearly 14,000 feet above a level interior, which apparently contains no conspicuous features.

EAST LONGITUDE 60 deg. TO 90 deg.

GRIMALDI.--This ranks among the largest wall-surrounded plains on the moon, and is perhaps the darkest. It extends 148 miles from N. to S. and 129 miles from E. to W., enclosing an area of some 14,000 square miles, or nearly double that of the princ.i.p.ality of Wales. This vast dusky surface is bounded on the E. by a tolerably regular border, having an average height of about 4000 feet, while on the opposite side it is much broken, and in places considerably loftier, rising at one peak on the S.W. to an alt.i.tude of 9000 feet. About midway, also, this western rampart attains a great height, as may be seen by any one who observes at sunrise the magnificent shadow of it, and its many peaks thrown across the bluish-grey interior. On the S. the wall is broken by a large irregular depression, on the W. of which is a very curious V-shaped rill valley. On the N.W. it is comparatively low, and in places discontinuous; and even to a greater extent than on the S.W., intersected by pa.s.ses. At the extreme N. end, a number of wide valleys cut through the wall and trend towards Lohrmann. There is a considerable ring-plain at the inner foot of the N.E. wall, but, except this and a few longitudinal ridges, just visible under a very low sun, there is apparently no other object to vary the monotony of this great expanse.

DAMOISEAU.--Consists of a complex arrangement of rings, an enclosure 23 miles in diameter, with a somewhat smaller enclosure placed excentrically within it (the N. side of both ab.u.t.ting on a bright plateau), with two large depressions intervening between their W. borders. This peculiarity, almost unique, renders the formation an especially interesting object.

Damoiseau is situated on the W. side of Grimaldi, on the E. coast-line of the Ocea.n.u.s Procellarum, from which the S.W. border rises at a gentle inclination. On the N.W. there is a curious curved inflexion of the Mare, bounded by a bright cliff, representing probably the E. side of a destroyed ring, a supposition which is strengthened by the existence of a faint scar on the surface of the sea, extending in a curve from one extremity of the bay to the other, and thus indicating the position of the remainder of the ring. A conspicuous little crater stands at the S.

end of it, and two others some distance to the W. The smaller component of Damoiseau contains a low central ridge.

RICCIOLI.--An immense enclosure, near the limb, N.E. of Grimaldi, bounded by a rampart which is very irregular both in form and height, though nowhere of great alt.i.tude, and much broken by narrow gaps. It is especially low and attenuated on the N., where a number of ridges with intervening valleys traverse it. On the S. also a wide valley cuts through it. With the exception of a few low rounded hills and ridges, a short crater-row under the S.E. wall, and two small craters on the S.W., there are no details on the floor, which, however, is otherwise remarkable for the dusky tone of its surface, especially on the N. This dark patch occupies the whole of the N.E. side of the interior, and is bounded on the S. by an irregular outline, extending at one point nearly to the centre, and on the W. by a curved edge. The W. side is much darker than the rest. It is, in fact, as dark, if not darker, than any part of the floor of Grimaldi. Riccioli extends 106 miles from N. to S., and is nearly as broad. It includes an area of 9000 square miles.

ROCCA.--An irregular formation, 60 miles in length, near the limb S.E. of Grimaldi, consisting of a depression partially enclosed by mountain arms.

SIRSALIS.--The more westerly of a conspicuous pair of ring-plains about 20 miles in diameter, in the disturbed mountain region some distance S.W.

of Grimaldi. It has lofty bright walls, rising to a great height above a depressed floor, on which there is a prominent central mountain. The E.

border encroaches considerably on the somewhat larger companion, which is, however, scarcely a third so deep. One of the longest clefts on the visible surface runs immediately W. of this formation. Commencing at a minute crater on the N. of it, it grazes the foot of the W. _glacis_; then, pa.s.sing a pair of small overlapping craters (resembling Sirsalis and its companion in miniature), it runs through a very rugged country to a ring-plain E. of De Vico (De Vico _a_), which it traverses, and, still following a southerly course, extends towards Byrgius, in the neighbourhood of which it is apparently lost at a ridge, though Schmidt and Gaudibert have traced it still farther in the same direction. It is at least 300 miles in length, and varies much in width and character, consisting in places of distinct crater-rows.

CRUGER.--A regular ring-plain E. of Fontana, 30 miles in diameter, with a dark floor, without detail, and comparatively low bright walls. There is a smaller but very conspicuous ring-plain (Cruger _a_) on the W. of it, to which runs a branch of the great Sirsalis cleft.

EICHSTADT.--A ring-plain, 32 miles in diameter, near the E. limb, S. of Rocca. It is the largest and most southerly of three nearly circular enclosures, without central mountains or any other details of interest.

On the W. lies a great walled-plain with a very irregular border, containing several ring-plains and craters, and a crater-rill. Schmidt has named this formation DARWIN.

BYRGIUS.--A very irregular enclosure, about 40 miles in diameter, between Cavendish and the E. limb, with a lofty and discontinuous border, rising at one point on the E. to a height of 7000 feet above the floor. There are wide openings both in the N. and S. wall, and some ridges within. The border is broken on the E. by a crater, and on the W. by the well-known crater Byrgius A, from which a number of bright streaks radiate, mostly towards the E. One on the W. extends to Cavendish, and another to Mersenius, traversing the ring-plain Cavendish C. North-east of Byrgius there is a mountain arm which includes a peak 13,000 feet in height.

PIAZZI.--A walled-plain, about 90 miles in length, some distance S.E. of Vieta, with a complex broken border, including several depressions on the N.W., rising to about 7000 feet above a rather dark interior, on which there is a prominent central mountain.

LAGRANGE.--A larger but similar formation, 100 miles in diameter, a.s.sociated with the last on the N.E., with a complex terraced border, including peaks of 9000 feet, a bright crater on the W., and a ring-plain on the N.W. The inner slope of the E. wall is a fine object at sunrise, when libration is favourable. The floor is dark and devoid of detail.

BOUVARD.--A great irregular enclosure, which appears to be still larger than Lagrange, S.E. of Piazzi, and close to the limb. It is bounded by a very lofty rampart, rising at a peak on the W. to 10,000 feet. It has a fine central mountain.

INGHIRAMI.--A very remarkable ring-plain, 60 miles in diameter, E. of Schickard, with a bright, broad, and nearly continuous border, terraced within, and intersected on the N.E. by narrow valleys, one of which is prolonged over the floor and extends to the central mountain. There are two curious dark spots on the N. side of the interior. Beyond the foot of the _glacis_ on the S. a distinct cleft runs from a dusky spot to a group of small craters E. of Wargentin. There is a fine regular ring-plain with a small central mount W. of Inghirami.

PINGRE.--A ring-plain, about 18 miles in diameter, between Phocylides and the limb.

HAUSEN.--A ring-plain, close to the limb, N. of Bailly, which, but for its position, would be a fine object. It is, however, never sufficiently well placed for observation.

BAILLY.--One of the largest wall-surrounded plains on the moon, almost a "sea" in miniature, extending 150 miles from N. to S., and fully as much from W. to E. When caught at a favourable phase, it is, despite its position, especially worthy of scrutiny. The rampart on the W., of the linear type, is broken by several bright craters. On the S.W. two considerable overlapping ring-plains interfere with its continuity. On the S.E. several very remarkable parallel curved valleys traverse the border. The E. wall, which at one point attains a height of nearly 15,000 feet, is beautifully terraced. The floor on the eastern side includes several ring-plains (some of which are of a very abnormal type), many ridges, and two delicate dark lines, crossing each other near the S. end, probably representing clefts.

LEGENTIL.--A large walled-plain, close to the limb, S. of Bailly.

FOURTH QUADRANT

WEST LONGITUDE 90 deg. TO 60 deg.

KASTNER.--A large walled-plain at the S. end of the Mare Smythii, too near the limb for satisfactory observation.

MACLAURIN.--The princ.i.p.al member of a group of irregular ring-plains on the W. side of the Mare Foecunditatis, a little S. of the lunar equator.

Schmidt shows no details within it, except a small crater on the E. side of the floor.

WEBB.--A ring-plain E. of Maclaurin, about 14 miles in diameter, with a dusky floor, enclosed by a bright rim, on the N.E. side of which there is a small crater. Schmidt seems to have overlooked the central hill.

LANGRENUS.--This n.o.ble circ.u.mvallation, the most northerly of the meridional chain of immense walled-plains, extending for more than 600 miles from near the equator to S. lat. 40 deg., would, but for its propinquity to the limb, rank with Copernicus (which in many respects it resembles) among the most striking objects on the surface of the moon.

Its length is about 90 miles from N. to S., and its breadth fully as much. In shape it approximates very closely to that of a foreshortened regular hexagon. The walls, which at one point on the E. rise to an alt.i.tude of nearly 10,000 feet, are continuous, except on this side, where they are broken by the interference of an irregular depression, and on the extreme S., where they are intersected by cross-valleys. Within, the terraces are remarkably distinct, and the intervening valleys strongly marked. The brilliant compound central mountain rises at its loftiest peak to a height of more than 3000 feet. On the N. of it is an obscure circular ring, which may possibly merely represent a fortuitous combination of ridges, though it has all the appearance of a modified ring-plain. On the Mare, some distance N.E. of the formation, is a group of three ring-plains, with two small craters (a.s.sociated with a ridge) on the N. of them. Two of the more westerly of these objects have prominent central mountains, and the third a very dark interior. At least three bright streaks originate on the E. flank of Langrenus, which, diverging widely, traverse the Mare Foecunditatis.

[FLATTENINGS ON THE MOON'S WESTERN LIMB.--About thirty years ago, the Rev. Henry Cooper Key drew attention to certain flattenings which he had noted on the W. limb, which are very apparent under favourable conditions of libration. Their position cannot be closely defined, but the princ.i.p.al deviation from circularity extends from about S. lat. 10 deg. to the region on the limb opposite the S. border of the Mare Crisium.]

VENDELINUS.--The second great enclosure pertaining to the meridional chain--a magnificent walled-plain of about the same dimensions as the last. It is bounded by a very irregular rampart, which, under evening illumination, is especially noteworthy, though nowhere approaching the alt.i.tude of that of Langrenus. Its continuity on the W. is broken by the great ring-plain Vendelinus C, about 50 miles in diameter, a formation resembling Langrenus in miniature. This is hexagonal in shape, and has many rings and depressions on its W. wall. South of Vendelinus C, the wall of Vendelinus runs up in a bold curve to the fine terraced ring- plain Vendelinus B, and is surmounted by a bright serpentine crest, and traversed by several valleys running down the slope to the floor. B has a small crater on its N. wall, and another in the interior. There is a wide gap in the S. border of Vendelinus, which is partially occupied by another somewhat smaller ring-plain, bounded by a southerly extension of the E. wall, which includes on its outer slope many craters and other depressions, and abuts near its N. end on the large ring-plain Vendelinus A, which has a prominently terraced wall and a large bright central mountain. Between A and C extends a plateau that may be regarded as the N. limit of the formation, including, among other minor details, a fine cleft, which traverses it from N. to S., and ultimately extends to a group of craters on the floor. On the S. side of the interior is one large ring-plain, flanked on the W. by two small craters. Near the N. end are many bright little craters, many of them unrecorded. Vendelinus C is bordered on the E. by two large semicircular formations with low walls extending on to the floor. Mr. W.H. Maw and others have detected many minute depressions in connection with these curious objects; and N. of them, on the outer slope of C, where it runs out to the level of the plateau, I have seen the surface at sunset riddled like a sieve with craterlets and little pits. There is an irregular ring-plain N. of A, with linear walls, and another, much smaller and brighter, on the N. of this, standing a little beyond the N. limits of Langrenus.

LA PEYROUSE.--A much foreshortened walled-plain, 41 miles in diameter, close to the limb, S.W. of Langrenus. There is a longitudinal ridge on the floor. Between it and Langrenus are two large ring-plains with central mountains, and on the N.E., La Peyrouse A, a bright crater, adjoining which is La Peyrouse DELTA, one of the most brilliant spots on the moon.

ANSGARIUS.--A ring-plain, 50 miles in diameter, still nearer to the limb than the last.

BEHAIM.--A great ring-plain, 65 miles in diameter, S. of Ansgarius, and connected with it by ridges. It has lofty walls and a central mountain.

HECATAEUS.--An immense walled-plain, 115 miles in length, on the S.W. of Vendelinus, with a very irregular rampart and a conspicuous central mountain. It is flanked E. and W. by other large enclosures, which can only be seen to advantage when libration is favourable.

W. HUMBOLDT.--Though close to the limb, this enormous wall-surrounded plain, some 130 miles in extreme length, and estimated to have an area of 12,000 square miles, is well worth observing under suitable conditions.

It ranks among the largest formations of its cla.s.s, and in many respects resembles Bailly on the S.E. limb. At one point on the E. a peak rises to 16,000 feet, and on the opposite side there are peaks nearly as high. The floor contains some detail--a crater, nearly central, a.s.sociated with ridges, and two dark spots, one at the S. and the other at the N. end.

PHILLIPS.--Abuts on the E. side of W. Humboldt. It is a walled-plain, about 80 miles in length, with a border much broken on the E., and terraced within on the opposite side. There are many hills and ridges on the floor.

LEGENDRE.--A fine ring-plain, 46 miles in diameter, on the S.E. of the last. According to Schmidt, there is a crater on the S. side of the floor. There is a small ring-plain, ADAMS, on the S.

PETAVIUS.--The third member of the great meridional chain: a n.o.ble walled-plain, with a complex rampart, extending nearly 100 miles from N.

to S., which encloses a very rugged convex floor, traversed by many shallow valleys, and includes a ma.s.sive central mountain and one of the most remarkable clefts on the visible surface. To observe these features to the best advantage, the formation should be viewed when its W. wall is on the evening terminator. At this phase a considerable portion of the interior on the N. is obscured by the shadow of the rampart, but the princ.i.p.al features on the S. half of the floor, and on the broad gently- shelving slope of the W. wall, are seen better than under any other conditions. The border is loftiest on the E., where the ring-plain Wrottesley abuts on it. It rises at this point to nearly 11,000 feet, while on the opposite side it nowhere greatly exceeds 6000 feet above the interior. The terraces, however, on the W. are much more numerous, and, with the a.s.sociated valleys, render this section of the wall one of the most striking objects of its cla.s.s. The N. border is conspicuously broken by the many valleys from the region S. of Vendelinus, which run up to and traverse it. On the S., also, it is intersected by gaps, and in one place interrupted by a large crater. There is a remarkable bifurcation of the border S. of Wrottesley. A lower section separates from the main rampart and, extending to a considerable distance S.E. of it, encloses a wide and comparatively level area which is crossed by two short clefts. The central mountains of Petavius, rising at one peak to a height of nearly 6000 feet above the floor, form a n.o.ble group, exceeding in height those in Ga.s.sendi by more than 2000 feet. The convexity of the interior is such that the centre of it is about 800 feet higher than the margin, under the walls; a protuberance which would, nevertheless, be scarcely remarked _in situ_, as it represents no steeper gradient than about 1 in 300 on any portion of its superficies. The great cleft, extending from the central mountains to the S.E. wall, and perhaps beyond, was discovered by Schroter on September 16, 1788, and can be seen in a 2 inch achromatic.

In larger instruments it is found to be in places bordered by raised banks.

WROTTESLEY.--A formation, about 25 miles in diameter, closely a.s.sociated with the E. wall of Petavius, the shape of which it has clearly modified.

Its border on the E., of the linear type, rises nearly 9000 feet above a light interior, where there is a small bright central mountain and some mounds. There is a prominent valley running along the inner slope of the W. wall.

PALITZSCH.--If this extraordinary formation is observed when the moon is about three days old, it resembles a great trough, or deep elongated gorge flanking the W. wall of Petavius, though it is a true ring-plain, albeit of a very abnormal type, about 60 miles in length and 20 miles in breadth, with a somewhat dusky interior. On the outer slope of its W.

wall is a bright ring-plain with a lofty border and a central mountain.

HASE.--An irregular formation, about 50 miles in diameter, on the S.W. of Petavius, with which it is connected by extensions of the W. and E. walls of the latter. Its rampart, some 7000 feet above the floor, is broken by depressions on the W.; and on the S. is bounded by a smaller ring-plain with still loftier walls. Schmidt shows a large crater and three smaller ones on the W. side of the floor.

MARINUS.--A ring-plain on the N.E. side of the Mare Australe, between Furnerius and the limb.

FURNERIUS.--The fourth and most southerly component of the great meridional chain of walled-plains, commencing on the N. with Langrenus: a fine but irregular enclosure, about 80 miles in extreme length and much more in breadth. Its rampart is very lofty, and tolerably continuous on the N. and W., but on the other sides is interrupted by small craters and depressions. At peaks on the E. it attains a height of more than 11,000 feet above the interior, and there are other peaks rising nearly as high.

There is a ring-plain (Furnerius B) with a central hill, on the E. side of the floor, and numerous craters and crater-pits in other parts of it.

On the N.W. side of B there is a short cleft, on the W., a well-marked crater-row, and on the E. a long rill-valley. The very brilliant crater (Furnerius A) on the N.E. _glacis_ is the origin of two fine light streaks, one extending S. for more than 100 miles, and the other in the opposite direction for a great distance.

FRAUNHOFER.--A ring-plain, S. of Furnerius, about 30 miles in diameter, with a regular border rising about 5000 feet above the floor. A smaller ring-plain abuts on the N.E. side of it, which has slightly disturbed its wall.