range, Mount Huygens, is at least 18,000 feet high,
and the black silhouettes of their sharp-pointed shadows thrown upon the
smooth floor of the _Mare Imbrium_ about the time of first quarter
present a spectacle as beautiful as it is unique. The Apennines end at
the southeast in the ring mountain, Eratosthenes, thirty-eight miles
across and very deep, one of its encircling chain of peaks rising 16,000
feet above the floor, and about half that height above the level of the
_Mare Imbrium_. The shadows cast by Eratosthenes at sunrise are
magnificent.

And now we come to one of the supreme spectacles of the moon, the
immense ring or crater mountain Copernicus. This is generally regarded
as the grandest object that the telescope reveals on the earth's
satellite. It is about fifty-six miles across, and its interior falls to
a depth of 8,000 feet below the _Mare Imbrium_. Its broad wall, composed
of circle within circle of ridges, terraces, and precipices, rises on
the east about 12,000 feet above the floor. On the inner side the slopes
are very steep, cliff falling below cliff, until the bottom of the
fearful abyss is attained. To descend those precipices and reach the
depressed floor of Copernicus would be a memorable feat for a
mountaineer. In the center of the floor rises a complicated mountain
mass about 2,400 feet high. All around Copernicus the surface of the
moon is dotted with countless little crater pits, and splashed with
whitish streaks. Northward lie the Carpathian Mountains, terminating on
the east in Tobias Mayer, a ring mountain more than twenty miles across.
The mountain ring Kepler, which is also the center of a great system of
whitish streaks and splashes, is twenty-two miles in diameter, and
notably brilliant.

Finally, we turn to the southeastern quadrant of the moon, represented
in Lunar Chart No. 4. The broad, dark expanse extending from the north
is the _Mare Nubium_ on the west and the _Oceanus Procellarum_ on the
east. Toward the southeast appears the notably dark, rounded area of the
_Mare Humorum_ inclosed by highlands and rings. We begin with the range
of vast inclosures running southward near the central meridian, and
starting with Ptolemaeus, a walled plain one hundred and fifteen miles in
its greatest diameter and covering an area considerably exceeding that
of the State of Massachusetts. Its neighbor toward the south, Alphonsus,
is eighty-three miles across. Next comes Arzachel, more than sixt