The Moon Part 8

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 n.o.ble 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 cla.s.s.

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 a.s.sociated 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 cla.s.s. 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 ma.s.sive 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 pa.s.ses, 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 ma.s.sive irregular border ab.u.t.ting 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 circ.u.mvallation; two, some distance apart, ab.u.t.ting 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 alt.i.tude surpa.s.ses many terrestrial mountain systems--as, for example, the Snowdonian group. The ma.s.sive barrier between Alpetragius and Alphonsus deserves careful scrutiny, and should be examined under a moderately low morning sun. On the E., towards La.s.sell, stands a brilliant light-surrounded crater.

ARZACHEL.--Another magnificent object, a.s.sociated on the N. with Alphonsus, about 66 miles in diameter, and encircled by a ma.s.sive 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.

La.s.sELL.--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. pa.s.ses. There is another crater on the opposite side. The central mountain is small and difficult to see.

About 20 miles N.E. of La.s.sell is a remarkable mountain group a.s.sociated 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 ma.s.ses 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 encompa.s.sed by a bright border, which, at a point on the E., is nearly 5000 feet in height. It is intersected on the N. by pa.s.ses 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, ab.u.t.ting 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 pa.s.s 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 alt.i.tude, and include many depressions, large and small. On the E. inner slope are some fine terraces and several craters. The continuity of the circ.u.mvallation 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.

REGIOMONTa.n.u.s.--A still more irregular walled-plain, of about the same area, closely a.s.sociated with the S. flank of Purbach, having a rampart of a similar complex type, traversed by pa.s.ses, 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 Regiomonta.n.u.s, 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 a.s.sociation 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.

h.e.l.l.--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.