Part 20

HOMMEL.--Adjoins Vlacq on the S. It is a somewhat larger and a far more irregular formation. On every side except the W., where the border is unbroken, and descends with a gentle slope to the dark interior; ring- plains and smaller depressions encroach on its outline, perhaps the most remarkable being Hommel a on the N., which has an especially brilliant wall, that includes a conspicuous central mountain, a large crater, and other details. The best phase for observing Hommel and its surroundings is when the W. wall is just within the evening terminator.

PITISCUS.--The most regular of the Vlacq group. It is situated on the N.E. of Hommel (a curious oblong-shaped enclosure, Hommel h, with a very attenuated E. wall, and a large crater on a floor, standing at a higher level than that of Pitiscus, intervening). It is 52 miles in diameter, and is surrounded by an apparently continuous rampart, except on the E., where there is a crater, and on the S.W., where it abuts on Hommel h. Here there is a wide gap crossed by what has every appearance of being a "fault," resembling that in Phocylides on a smaller scale. There is a fine crater on the N. side of the interior connected with the S. wall by a bright ridge. Just beyond the E. border there is a shallow ring-plain of a very extraordinary shape.

NEARCH.--A ring-plain, about 35 miles in diameter, on the S.W. of Hommel, forming part of the Vlacq group.

TANNERUS.--A ring-plain, about 19 miles in diameter, between Mutus and Bacon. It has a central mountain.

MUTUS.--A fine but foreshortened walled plain, 51 miles in diameter. There are two ring-plains of about equal size on the floor, one on the N., and the other on the S. side. The wall on the W. rises to nearly 14,000 feet above the interior.

MANZINUS.--A walled plain, nearly 62 miles in diameter, with a terraced rampart rising to a height of more than 14,500 feet above the interior. Schmidt shows three craterlets on the floor, but no traces of the small central peak which is said to stand thereon, but to be only visible in large telescopes.

SCHOMBERGER.--A large walled-plain adjoining Simpelius on the S.W. Too near the limb for satisfactory observation.

WEST LONGITUDE 20 deg. TO 0 deg.

DELAMBRE.--A conspicuous ring-plain, 32 miles in diameter, a little S. of the equator, in W. long. 17 deg. 30 min., with a massive polygonal border, terraced within, rising on the W. to the great height of 15,000 feet above the interior, but to little more than half this on the opposite side. Its outline approximates to that of a pentagon with slightly curved sides. A section on the S.E. exhibits an inflexion towards the centre. The crest is everywhere continuous except on the N., where it is broken by a deep crater with a bright rim. The north-easterly trend of the ridges and hillocks on the E. is especially noteworthy. The central peak is not prominent, but close under it on the E. is a deep fissure, extending from near the centre, and dying out before it reaches the S. border. At the foot of the N.E. glacis there are traces of a ring with low walls.

THEON, SEN.--A brilliant little ring-plain, E.N.E. of Delambre, 11 miles in diameter, and of great depth, with a regular and perfectly unbroken wall. North of it is a bright little crater.

THEON, JUN.--A ring-plain similar in size and in other respects to the last, situated about 23 miles S. of it on a somewhat dusky surface. Between the pair is a curious oblong-shaped mountain mass; and on the E. a long cliff (of no great altitude, but falling steeply on the E. side) extending S. towards Taylor a. Just below the escarpment, I find a brilliant little pair of craterlets, of which Neison only shows one.

ALFRAGANUS.--A large bright crater, about 9 miles in diameter, with very steep walls, some distance S.S.W. of Delambre, and standing on the W. edge of a large but very shallow and irregular depression W. of Taylor. There is a remarkable chain of craters on the W. of it. Alfraganus is the centre of a system of light streaks radiating in all directions, one ray extending through Cyrillus to Fracastorius.

TAYLOR.--A deep spindle-shaped ring-plain, S. of Delambre, about 22 miles in length. The wall appears to be everywhere continuous, except at the extreme N. and S. ends, where there are small craters. The outer slopes, both on the E. and W., are very broad and prominent, but apparently not terraced. There is an inconspicuous central hill. On the W. is the irregular enclosure, already referred to under Alfraganus. Three or four short winding valleys traverse the N. edge of this formation, and descend to the dark floor. On the N.E. is the remarkable ring-plain Taylor a, 18 miles in diameter, rising, at an almost isolated mountain mass on the E. border, to a height of 7000 feet above the interior. The more regular and W. section of this formation is not so lofty, and falls with a gentle slope to the dark uneven floor, on which there is some detail in the shape of small bright ridges and mounds. On the surface, N.W. of Taylor a, is a curious linear row of bright little hills. Taylor and the vicinity is better seen under low evening illumination than under morning light.

HIPPARCHUS.--Except under a low sun, this immense walled-plain is by no means so striking an object as a glance at its representation on a chart of the moon would lead one to expect; for the border, in nearly every part of it, bears unmistakable evidence of wreck and ruin, its continuity being interrupted by depressions, transverse valleys, and gaps, and it nowhere attains a great altitude. This imperfect enclosure extends 97 miles from N. to S., and about 88 miles from E. to W., and in shape approximates to that of a rhombus with curved sides. One of the most prominent bright craters on its border is Hipparchus G, on the W. Another, of about the same size, is Hipparchus E, on the N. of Horrocks. On the E. there is a moderately bright crater, Hipparchus F; and S. of this, on the same side, two others, K and I. The interior is crossed by many ridges, and near the centre includes the relics of a low ring, traversed by a narrow rill-like valley. Schmidt shows a cleft running from F across the floor to the S. border.

HORROCKS.--This fine ring-plain, 18 miles in diameter, stands on the N. side of the interior of Hipparchus, close to the border. It has a continuous wall, rising on the E. to a height of nearly 8000 feet above the interior, and a distinct central mountain.

HALLEY.--A ring-plain, 21 miles in diameter, on the S.W. border of Hipparchus, with a bright wall, rising at one point on the E. to a height of 7500 feet above the floor, which is depressed about 4000 feet below the surface. Two craterlets on the floor, one discovered by Birt on Rutherfurd's photogram of 1865, and the other by Gaudibert, raised a suspicion of recent lunar activity within this ring. A magnificent valley, shown in part by Schmidt as a crater-row, runs from the S. of Halley to the W. side of Albategnius.

HIND.--A ring-plain, 16 miles in diameter, a few miles W. of Halley, with a peak on its E. wall 10,000 feet above the floor. The border is broken both on the S.E. and N.E. by small craters.

ALBATEGNIUS.--A magnificent walled-plain, 65 miles in diameter, adjoining Hipparchus on the S., surrounded by a massive complex rampart, prominently terraced, including many depressions, and crossed by several valleys. It is surmounted by very lofty peaks, one of which on the N.E. stands nearly 15,000 feet above the floor. The great ring-plain Albategnius A, 28 miles in diameter, intrudes far within the limits of the formation on the E., and its towering crest rises more than 10,000 feet above its floor, on which there is a small central mountain. The central mountain of Albategnius is more than 4000 feet high, and, with the exception of a few minor elevations, is the only prominent feature in the interior, though there are many small craters. Schmidt counted forty with the Berlin refractor, among them 12 on the E. side, arranged like a string of pearls.

PARROT.--An irregularly-shaped formation, 41 miles in diameter, S. of Albategnius, with a very discontinuous margin, interrupted on every side by gaps and depressions, large and small; the most considerable of which is the regular ring-plain Parrot a, on the E. An especially fine valley, shown by Schmidt to consist in part of large inosculating craters, cuts through the wall on the S.W., and runs on the E. side of Argelander towards Airy. The floor of Parrot is very rugged.

DESCARTES.--This object, about 30 miles in diameter, situated N.W. of Abulfeda, is bounded by ill-defined, broken, and comparatively low walls; interrupted on the S.E. by a fine crater, Descartes A, and on the S.W. by another, smaller. There is also a brilliant crater outside on the N.W. Schmidt shows a crater-row on the floor, which I have seen as a cleft.

DOLLOND.--A bright crater, about 6 miles in diameter, on the N.E. side of Descartes. Between it and the latter there is a rill-valley.

TACITUS.--A bright ring-plain, about 28 miles in diameter, a few miles E. of Catherina, with a lofty wall rising both on the E. and W. to more than 11,000 feet above the floor. Its continuity is broken on the N. by a gap occupied by a depression, and there is a conspicuous crater below the crest on the S.W. The central mountain is connected with the N. wall by a ridge, recalling the same arrangement within Madler. A range of lofty hills, an offshoot of the Altai range, extends from Tacitus towards Fermat.

ALMANON.--This ring-plain, with its companion Abulfeda on the N.E., is a very interesting telescopic object. It is about 36 miles in diameter, and is surrounded by an irregular border of polygonal shape, the greatest altitude of which is about 6000 feet above the floor on the W. It is slightly terraced, and is broken on the S. by a deep crater pertaining to the bright and large formation Tacitus b, the E. border of which casts a fine double-peaked shadow at sunrise. On the N.W. there is another bright crater, the largest of the row, running in a W.S.W. direction, and forming a W. extension of the remarkable crater-chain tangential to the borders of Almanon and Abulfeda. The only objects on the floor are three little hills, in a line, near the centre, a winding ridge on the W. side of it, and two or three other low elevations.

ABULFEDA.--A larger and more massive formation than Almanon, 39 miles in diameter, the E. wall rising about 10,000 feet above the interior, which is depressed more than 3000 feet. It is continuous on the W., but much broken by transverse valleys on the S.E., and by little depressions on the N. On the S.E. originates the very curious bright crater-row which runs in a straight line to the N.W. wall of Almanon, crossing for the first few miles the lofty table-land lying on the S.E. side of the border. With the exception of a low central mountain, the interior of Abulfeda contains no visible detail. The rampart is finely terraced on the E. and W. The E. glacis is very rugged.

ARGELANDER.--This conspicuous ring-plain, about 20 miles in diameter, is, if we except two smaller inosculating rings on the S.W. flank of Albategnius, the most northerly of a remarkable serpentine chain of seven moderately-sized formations, extending for nearly 180 miles from the S.W. of Parrot to the N. side of Blanchinus. Its border is lofty, slightly terraced within, and includes a central peak.

AIRY.--About 22 miles in diameter, connected with Argelander by a depression bounded by linear walls. Its border, double on the S.E., is broken on the S. by a prominent crater, with a smaller companion on the W. of it; and again on the N.E. by another not so conspicuous. It has a central peak. The next link in the chain of ring-plains is Airy c, a very irregular object, somewhat larger, and with, for the most part, linear walls.

DONATI.--A ring-plain on the S. of Airy c, about 22 miles in greatest length. It is very irregular in outline, with a lofty broken border, especially on the N. and S., where there are wide gaps. There is another ring on the S.E.

FAYE.--The direction of the chain swerves considerably towards the E. at this formation, which resembles Donati both in size and in irregularity of outline. The wall, where it is not broken, is slightly terraced. There is a craterlet on the S. rim and a central crater in the interior.