BESSEL.—­A bright circular crater, 14 miles in diameter, on the S. half of the Mare Serenitatis, and the largest object of its class thereon.  Its floor is depressed some 2000 feet below the surrounding surface, while the walls, rising nearly 1600 feet above the plain, have peaks both on the N. and S. about 200 feet higher.  The shadows of these features, noted by Schroter in 1797, and by many subsequent observers, are very noteworthy.  I have seen the shadow of a third peak about midway between the two.  One may faintly imagine the magnificent prospect of the coast-line of the Mare with the Haemus range, which would be obtained were it possible to stand on the summit of one of these elevations.  It is doubtful whether Bessel has a central mountain.  Neither Madler nor Schmidt have seen one, though Webb noted a peak on two occasions.  I fail to see anything within the crater.  The bright streak crossing the Mare from N. to S. passes through Bessel.

LINNE.—­A formation on the E. side of the Mare Serenitatis, described by Lohrmann and Madler as a deep crater, but which in 1866 was found by Schmidt to have lost all the appearance of one.  The announcement of this apparent change led to a critical examination of the object by most of the leading observers, and to a controversy which, if it had no other result, tended to awaken an interest in selenography that has been maintained ever since.  According to Madler, the crater was more than 6 miles in diameter in his time, and very conspicuous under a low sun, a description to which it certainly did not answer in 1867 or at any subsequent epoch.  It is anything but an easy object to see well, as there is a want of definiteness about it under the best conditions, though the minute crater, the low ridges, and the nebulous whiteness described by Schmidt and noted by Webb and others, are traceable at the proper phase.  As in the case of Hyginus N, there are still many sceptics as regards actual change, despite the records of Lohrmann and Madler; but the evidence in favour of it seems to preponderate.

CONON.—­A bright little crater, 11 miles in diameter, situated among the intricacies of the Apennines, S. of Mount Bradley.  It has a central hill, which is not a difficult object.

ARATUS.—­One of the most brilliant objects on the visible surface of the moon, a crater 7 miles in diameter, S. of Mount Hadley, surrounded by the lofty mountain arms and towering heights of the Apennines.  A peak close by on the N. is more than 10,000 feet, and another farther removed towards the N.W. is over 14,000 feet in altitude.

AUTOLYCUS.—­A ring-plain 23 miles in diameter, deviating considerably from circularity, W. of Archimedes, on the Mare Imbrium, or rather on that part of it termed the Palus Putredinis.  Its floor, which contains an inconspicuous central mountain, is depressed some 4000 feet below the surrounding country.  With a power of 150 on a 4 5/8 achromatic, Dr. Sheldon of Macclesfield has seen two shallow crateriform depressions in the interior, one nearly central, and the other about midway between it and the N. wall.  The wall is terraced within, and has a crater just below its crest on the W., which, when the opposite border is on the morning terminator, is seen as a distinct notch.  Autolycus is the centre of a minor ray-system.