Chapter 16
FRACASTORIUS.--This great bay or inflexion at the extreme S. end of the Mare Nectaris, about 60 miles in diameter, is one of the largest and most suggestive examples of a partially destroyed formation to be found on the visible surface. The W. section of the rampart is practically complete and unbroken, rising at one peak to a height of 6000 feet above the interior. It is very broad at its S. end, and its inner slope descends with a gentle gradient to the floor. Towards the N., however, it rapidly decreases in width, but apparently not in altitude, till near its bright pointed N. extremity. Under a low sun, some long deformed crateriform depressions may be seen on the slope, and a bright little crater on the crest of the border near its N. end. The southern rampart is broken by three large craters, and a fine valley, running some distance in a S. direction, which diminishes gradually in width till it ultimately resembles a cleft, and terminates at a small crater. The E. border is very lofty and irregular, rising at the N. corner of the large triangular formation, which is such a prominent feature upon it, to a height of 7000 feet, and at a point on the S.E. to considerably more than 8000 feet above the floor. N. of the former peak it becomes much lower and narrower, and is finally only represented by a very attenuated strip of wall, hardly more prominent than the brighter portions of the border of Stadius at sunrise, terminating at an obscure semi-ring-plain. Between this and the pointed N. termination of the W. border there is a wide gap, open to the north for a space of about 30 miles, appearing, except under very oblique illumination, as smooth and as devoid of detail as the grey surface of the Mare Nectaris itself. If, however, this interval is observed at sunrise or sunset, it is seen to be not quite so structureless as it appears under different conditions, for a number of mounds and large humpy swellings, with low hills and craterlets, extend across it, and occupy a position which we are justified in regarding as the site of a section of the rampart, which, from some cause or other, has been completely destroyed and overlaid with the material, whatever this may be, of the Mare Nectaris. The floor of Fracastorius is, as regards the light streaks and other features upon it, only second in interest to those of Plato and Archimedes, and will repay systematic observation. Between thirty and forty light spots and craters have been recorded on its surface, most of them, as in these formations, being situated either on or at the edges of the light streaks. On the higher portion of the interior (near the centre) is a curious object consisting apparently of four light spots, arranged in a square, with a craterlet in the middle, all of which undergo (as I have pointed out elsewhere) notable changes of aspect under different phases. There are at least two distinct clefts on the floor, one running from the W. wall towards the centre, and another on the S.E. side of the interior. The last throws out two branches towards the S.W.
ROSSE.--A fine bright deep crater in the Mare Nectaris, N. of the pointed termination of the W. wall of Fracastorius, with which it is connected by a bold curved ridge, with a crater upon it. A ray from Tycho, striking along the E. wall of Fracastorius passes near this object. A rill from near Bohnenberger terminates at this crater.
POLYBIUS.--A ring-plain, about 17 miles in diameter, in the hilly region S.E. of Fracastorius. The border is unbroken, except on the N., where it is interrupted by a group of depressions. There is a long valley on the S.W., at the bottom of which Schmidt shows a crater-chain.
NEANDER.--This ring-plain, 34 miles in diameter, a short distance W.S.W. of Piccolomini, has a somewhat deformed rampart, which, however, except on the N., where there is a narrow gap occupied by a small crater, is continuous. It rises on the E. nearly 8000 feet above the floor, on which there is a central mountain about 2500 feet high. Schmidt shows some minor hills, a large crater on the N.E. side, and three smaller craters in the interior.
PICCOLOMINI.--A ring-plain of a very massive type, about 57 miles in diameter, S. of Fracastorius, with complex and prominently terraced walls, surmounted by very many peaks; one of which on the E. attains a height of 14,000 feet, and another, N. of it, on the same side, an altitude of 15,000 feet above the interior. The crest of this grand rampart is tolerably continuous, except on the S.W., where, for a distance of twenty miles or more, its character as regards form and brightness is entirely changed. Under a low sun, instead of a continuous bright border, we note a wide gap occupied by a dusky rugged plateau, which falls with a gentle gradient to the floor, and is traversed by three or four parallel shallow valleys running towards the S. I can recall no lunar formation which presents an appearance at all like this: one is impressed with the idea that it has resulted from the collapse of the upper portion of the wall, and the flow of some viscous material over the wreck and down the inner slope. The difference between the reflective power of this matter, whatever may be its nature, and the broad bright declivities of the inner slopes, are beautifully displayed at sunset. The cross-valleys are more easily traced under low morning illumination; but to appreciate the actual structure of the wall, it should be observed under both phases. The N.W. section of the border includes many "pockets," or long elliptical depressions, which at an early stage of sunrise give a scalloped appearance to the crest. Except the great bright central mountain with its numerous peaks, there does not appear to be any prominent detail on the floor. There is a large ring-plain beyond the foot of the _glacis_ on the W. with two craters on the E. side of it, another on the S., and a fine rill-valley running up to its N. side from near the crest of the W. wall. On the N. side of Piccolomini is a remarkable group of deformed and overlapping enclosures, mingled with numberless craters and little depressions. The plain on the N.E. is crossed by a fine cleft.
PONS.--A complete formation of irregular shape, about 20 miles in greatest diameter, on the S.E. side of the Altai range, in W. long. 21 deg. It consists of a crowd of rings and craters enclosed by a narrow wall.
STIBORIUS.--An elongated ring-plain, about 22 miles in diameter, S. of Piccolomini, with a lofty wall, broken in one place on the N. by a very conspicuous crater. Schmidt shows a distinct crater in the centre of the floor. I have only seen a central mountain in this position. There is a large crater on the N.W., a ring-plain on the S.W. side, and a multitude of little craters on the surrounding plain.
RICCIUS.--A ring-plain, 51 miles in diameter, of a very irregular type, S.E. of the last. It is enclosed by a complex wall (which is in places double), broken by large rings on the S. The very conspicuous little ring-plain Riccius A is situated on the N. of it, and other less prominent features. The interior includes a bright crater and some smaller objects of the same class.
ZAGUT.--The most easterly of a group of closely associated irregular walled-plains, of which Lindenau and Rabbi Levi are the other members, all evidently deformed and modified in shape by their proximity. It is about 45 miles in diameter, and is enclosed by a wall which on the S.W. attains a height of about 9500 feet, and is much broken on the N. by a number of depressions. A large ring-plain, some 20 miles in diameter, occupies a considerable portion of the W. side of the interior; E. of which, and nearly central, there is a large bright crater, but apparently no other conspicuous details. On the S.E. side of Zagut lies an elliptical ring-plain, about 28 miles in diameter, named by Schmidt CELSIUS. The border of this is open on the N., the gap being occupied by a large crater, whose S. wall is wanting, so that the interiors of both formations are in communication.
LINDENAU.--This formation, about 35 miles in diameter, is bounded on the W. by a regular unbroken wall nearly 8600 feet in height; but which on the E. and N.E. is far loftier and more complex, rising to about 12,000 feet above the floor, consisting of four or more distinct ramparts, separated by deep valleys, and extending towards Rabbi Levi. Neison points out that under a high light Lindenau appears to have a bright uniform single wall. There is a small central mountain and some minor inequalities in the interior.
RABBI LEVI.--A larger but less obvious formation than either of its neighbours, Zagut and Lindenau, abutting on the S. side of them. It is about 55 miles in diameter, and is enclosed by a border somewhat difficult to trace in its entirety, except under oblique light. There are some large craters within it, of which one on the N. side of the floor is especially prominent.
NICOLAI.--A tolerably regular ring-plain, 18 miles in diameter, S. of Riccius, with a border, rising more than 6000 feet above a level floor, on the N. side of which Schmidt shows a minute crater. The bright plain surrounding this formation abounds in small craters; and on the W. is a number of curious enclosures, many of them overlapping.
VLACQ.--A member of a magnificent group of closely associated formations situated on the greatly disturbed area between W. long. 30 deg. and 45 deg. and S. lat. 50 deg. and 60 deg. It is 57 miles in diameter, and is enclosed by terraced walls, rising on the W. about 8000 feet, and on the E. more than 10,000 feet above the floor. They are broken on the S. by a fine crater. In addition to a conspicuous central peak, there are several small craters, and low short ridges in the interior.
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.
[A valuable monograph of Hipparchus, by Mr. W.B. Birt, was published in 1870.]
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.
[Horrocks, Halley, and Hind may be regarded as strictly belonging to Hipparchus.]
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.
DELAUNAY.--Adjoins Faye on the S.E., and is a larger and more complex object, of irregular form, with very lofty peaks on its border. A prominent ridge of great height traverses the formation from N. to S., abutting on the W. border of Lacaille. Delaunay is the last link in the chain commencing with Argelander.
LACAILLE.--An oblong enclosure situated on the N. side of Blanchinus, and apparently about 30 miles in greatest diameter. The border is to a great extent linear and continuous on the N., but elsewhere abounds in depressions. Two large inosculating ring-plains are associated with the N.E. wall.
BLANCHINUS.--A large walled-plain on the W. of Purbach and abutting on the S. side of Lacaille. It much resembles Purbach in shape, but has lower walls. Schmidt shows a crater on the N. side of the floor, which I have seen, and a number of parallel ridges which have not been noted, probably because they are only visible under very oblique light.
GEBER.--A bright ring-plain, 25 miles in diameter, S. of Almanon, with a regular border, rising to a height on the W. of nearly 9000 feet above the floor. There is a small crater on the crest of the S. wall, and another on the N. A ring-plain about 8 miles in diameter adjoins the formation on the N.E. According to Neison, there is a feeble central hill, which, however, is not shown by Schmidt.