tre, a peculiarity already noticed in the case of
Eratosthenes. The walls, tolerably uniform in height, are surmounted by a
great number of peaks, one of which on the W., according to Neison,
stands 11,000 feet above the floor, and a second on the opposite side is
nearly as high. Both the inner and outer slopes of this gigantic rampart
are very broad, each being fully 10 miles in width. The outer slope,
especially on the E., is a fine object at sunrise, when its rugged
surface, traversed by deep gullies, is seen to the best advantage. The
terraces and other features on the bright inner declivities on this side
may be well observed when the sun's altitude is about 6 deg. Schmidt,
whose measures differ from those of Neison, estimates the height of the
wall on the E. to be 12,000 feet, and states that the interior slopes
vary from 60 deg. to 50 deg. above, to from 10 deg. to 2 deg. at the
base. The first inclination of 50 deg., and in some cases of 60 deg., is
confined to the loftiest steep crests and to the flanks of the terraces.
There are apparently five bright little mountains on the floor, the most
easterly being rather the largest, and a great number of minute hillocks
on the S.E. quarter. S.W. of the centre is a little crater, and on the
same side of the interior a curious hook-shaped ridge, projecting from
the foot of the wall, and extending nearly halfway across the floor. The
region surrounding Copernicus is one of the most remarkable on the moon,
being everywhere traversed by low ridges, enclosing irregular areas,
which are covered with innumerable craterlets, hillocks, and other minute
features, and by a labyrinth of bright streaks, extending for hundreds of
miles on every side, and varying considerably both in width and
brilliancy.

The notable crater-row on the W., often utilised by observers for testing
the steadiness of the air and the definition of their telescopes, should
be examined when it is on the morning terminator, at which time Webb's
homely comparison, "a mole-run with holes in it," will be appreciated,
and its evident connection with the E. side of Stadius clearly made out.
There is another much more delicate row running closely parallel to this
object; it lies a little W. of it, and extends farther in a northerly
direction.

ARCHIMEDES.--Next to Plato the finest object on the Mare Imbrium. It is
about 50 miles in diameter. The average height of its massive border is
about 4000 feet above the in