STADIUS.—­An inconspicuous though a very interesting formation, 43 miles in diameter, W. of Copernicus, with a border scarcely exceeding 200 feet in height.  Hence it is not surprising that it was for a long time altogether overlooked by Madler.  Except as a known object, it is only traceable under very oblique illumination, and even then some attention is required before its very attenuated wall can be followed all round.  It is most prominent on the W., where it apparently consists of a S. extension of the Eratosthenes mountain-arm, and is associated with a number of little craters and pits.  This is succeeded on the S.W. by a narrow strip of bright wall, and on the S. by a section made up of a piece of straight wall and a strip curving inwards, forming the S. side.  On the E. the border assumes a very ghostly character, and appears to be mainly defined by rows of small depressions and mounds.  On the N.E., N., and N.W. it is still lower and narrower; so much so, that it is only for an hour or so after sunrise or before sunset that it can be traced at all.  On every side, with the exception of the curved piece on the S., the wall consists of linear sections.  The interior contains a great number of little craters and very low longitudinal mounds.  Ten craters are shown in Beer and Madler’s map.  Schmidt only draws fifteen, though in the text accompanying his chart he says that he once counted fifty.  In the monograph published in the Journal of the Liverpool Astronomical Society (vol. v. part 8), forty-one are represented.  They appear to be rather more numerous on the S. half of the floor than elsewhere.  Just beyond the limits of the border on the N., is a bright crater with a much larger obscure depression on the W. of it.  The former is surrounded by a multitude of minute craters and crater-cones, which are easily seen under a low sun.  Though almost every trace of Stadius disappears under a high light, I have had little difficulty in seeing portions of the border and some of the included details when the morning terminator had advanced as far as the E. wall of Herodotus, and the site was traversed by innumerable light streaks radiating from Copernicus.  At this phase the bright crater, just mentioned, on the N. edge of the border was tolerably distinct.

COPERNICUS.—­This is without question the grandest object, not only on the second Quadrant, but on the whole visible superficies of the moon.  It undoubtedly owes its supremacy partly to its comparative isolation on the surface of a vast plain, where there are no neighbouring formations to vie with it in size and magnificence, but partly also to its favourable position, which is such, that, though not central, is sufficiently removed from the limb to allow all its manifold details to be critically examined without much foreshortening.  There are some other formations, Langrenus and Petavius, for example, which, if they were equally well situated, would probably be fully