the rampart is about 3,800 feet on the eastern side; the western side is
somewhat lower, but there is one peak rising to the height of nearly
7,300 feet. The plain girdled by this vast rampart is of ample
proportions. It is a somewhat irregular circle, about 60 miles in
diameter, and containing an area of 2,700 square miles. On its floor the
shadows of the western wall are shown in Plate IX., as are also three of
the small craters, of which a large number have been detected by
persevering observers. The narrow sharp line leading from the crater to
the left is one of those remarkable "clefts" which traverse the moon in
so many directions. Another may be seen further to the left. Above Plato
are several detached mountains, the loftiest of which is Pico, about
8,000 feet in height. Its long and pointed shadow would at first sight
lead one to suppose that it must be very steep; but Schmidt, who
specially studied the inclinations of the lunar slopes, is of opinion
that it cannot be nearly so steep as many of the Swiss mountains that
are frequently ascended. As many as thirty minute craters have been
carefully observed on the floor of Plato, and variations have been
thought by Mr. W.H. Pickering to be perceptible.

9. _Eratosthenes._--This profound crater, upwards of 37 miles in
diameter, lies at the end of the gigantic range of the Apennines. Not
improbably, Eratosthenes once formed the volcanic vent for the
stupendous forces that elevated the comparatively craterless peaks of
these great mountains.

10. _Copernicus._--Of all the lunar craters this is one of the grandest
and best known. The region to the west is dotted over with innumerable
minute craterlets. It has a central many-peaked mountain about 2,400
feet in height. There is good reason to believe that the terracing shown
in its interior is mainly due to the repeated alternate rise, partial
congelation, and subsequent retreat of a vast sea of lava. At full moon
the crater of Copernicus is seen to be surrounded by radiating streaks.

11. _Kepler._--Although the internal depth of this crater is scarcely
less than 10,000 feet, it has but a very low surrounding wall, which is
remarkable for being covered with the same glistening substance that
also forms a system of bright rays not unlike those surrounding the last
object.

12. _Aristarchus_ is the most brilliant of the lunar craters, being
specially vivid with a low power in a large telescope. So bright is it,
indee