small central mountain, which is a good test for
moderate apertures.

GASSENDI.--One of the most beautiful telescopic objects on the moon's
visible surface, and structurally one of the most interesting and
suggestive. It is a walled-plain, 55 miles in diameter, of a distinctly
polygonal type, the N.W. and S.W. sections being practically straight,
while the intermediate W. section exhibits a slightly convex curvature,
or bulging in towards the interior. There is also much angularity about
the E. side, which is evident at an early stage of sunrise. The wall on
the N. is broken through and almost completely wrecked by the great ring-
plain Gassendi A. The bright eastern section of the border is in places
very lofty, rising at one peak, N. of the well-known triangular
depression upon it, to 9000 feet, and at other peaks on the same side
still higher. It is very low on the S., being only about 500 feet above
the surface. The floor, however, on the N. stands 2000 feet above the
Mare Humorum. On the W. there is a peak towering 4000 feet above the
wall, which is here about 5000 feet above the floor, and 8000 feet above
the Mare Nubium. A very notable feature in connection with this formation
is the little bright plain bounding it on the N.W., and separated from it
by merely a narrow strip of wall. This enclosure is flanked on the N.E.
by Gassendi A, and on the S.W. and N.W. by a coarse winding ridge,
running from the W. wall and terminating at a large irregular dusky
depression. Gaudibert has detected a crater near the S.E. edge of this
bright plain, which includes also some oval mounds. The interior of
Gassendi is without question unrivalled for the variety of its details,
and, after Plato, has perhaps received more attention from observers than
any other object. The bright central mountain, or rather mountains, for
it consists of a number of grouped masses crowned by peaks, of which the
loftiest is about 4000 feet, is one of the finest on the moon. It was
carefully studied with a 6 1/4 inch Cooke-achromatic by the late
Professor Phillips, the geologist, who compared it to the dolomitic or
trachytic mountains of the earth. The buttresses and spurs which it
throws out give its base a digitated outline, easily seen under suitable
illumination. There are between 30 and 40 clefts in the interior, the
majority being confined to the S.W. quarter of the floor. Those most
easily seen pertain to the group which radiates from the centra