or under
suitable illumination, among them a forked cleft on the N.E. quarter, and
two others, originating at a dusky pit of irregular form situated near
the foot of the S.E. wall, one of which runs W. of the central hills, and
the other on the opposite side. A ridge, at times resembling a light
marking, extends from the central mountain to the N. border. During the
years 1870 and 1871 I bestowed some attention on the dusky pit, and was
led to suspect that both it and the surrounding area vary considerably in
tone from time to time. Professor W.H. Pickering, observing the formation
in 1891 with a 13 inch telescope under the favourable atmospheric
conditions which prevail at Arequipa, Peru, confirmed this supposition,
and has discovered some very interesting and suggestive facts relating to
these variations, which, it is hoped, will soon be made public. On the
plain a short distance beyond the foot of the _glacis_ of the S.E. wall,
I have frequently noted a second dusky spot, from which proceeds, towards
the E., a long rill-like marking. On the N. there is a large formation
enclosed by rectilineal ridges. The outer slopes of the rampart of Atlas
are very noteworthy under a low sun.

HERCULES.--The eastern companion of Atlas, a fine ring-plain, about 46
miles in diameter, with a complex border, rising some 11,000 feet above a
depressed floor. There are few formations of its class and size which
display so much detail in the shape of terraces, apparent landslips, and
variation in brightness. In the interior, S.E. of the centre, is a very
conspicuous crater, which is visible as a bright spot when the formation
itself is hardly traceable, two large craterlets slightly N. of the
centre, and several faint little spots on the east of them. The latter,
detected some years ago by Herr Hackel of Stuttgart, are arranged in the
form of a horse-shoe. There are two small contiguous craters on the S.E.
wall, one of which, a difficult object, was recently detected by Mr. W.H.
Maw, F.R.A.S. The well-known wedge-shaped protuberance on the S. wall is
due to a large irregular depression. On the bright inner slope of the N.
wall are manifest indications of a landslip.

ENDYMION.--A large walled-plain, 78 miles in diameter, enclosed by a
lofty, broad, bright border, surmounted in places by peaks which attain a
height of more than 10,000 feet above the interior, one on the W.
measuring more than 15,000 feet. The walls are much terraced and exh