liant
in contrast with the surrounding plain, but out of that plain, about
forty miles toward the east, projects a small mountain which is also
remarkable for its reflecting properties, as if the gray ground were
underlain by a stratum of some material that flashes back the sunlight
wherever it is exposed. The crater mountain, Sulpicius Gallus, on the
border of the _Mare_, north of Manilius and east of Menelaus, is another
example of the strange shining quality of certain formations on the
moon.

Follow next the Haemus range westward until the attention falls upon the
great ring mountain Plinius, more than thirty miles across, and bearing
an unusual resemblance to a fortification. Mr. T. G. Elger, the
celebrated English selenographer, says of Plinius that, at sunrise, "it
reminds one of a great fortress or redoubt erected to command the
passage between the _Mare Tranquilitatis_ and the _Mare Serenitatis_."
But, of course, the resemblance is purely fanciful. Men, even though
they dwelt in the moon, would not build a rampart 6,000 feet high!

Mount Argaeus, at the southwest corner of the _Mare Serenitatis_, is a
very wonderful object when the sun has just risen upon it. This occurs
five days after the new moon.

Returning to the eastern extremity of the _Mare_, we glance, in passing,
at the precipitous Mount Hadley, which rises more than 15,000 feet above
the level of the _Mare_ and forms the northern point of the Apennine
range. Passing into the region of the _Mare Imbrium_, whose western end
is divided into the _Palus Putredinis_ on the south and the _Palus
Nebularum_ on the north, we notice three conspicuous ring mountains,
Cassini near the Alps, and Aristillus and Autolycus, a beautiful pair,
nearly opposite the strait connecting the two _Maria_. Cassini is
thirty-six miles in diameter, Aristillus thirty-four, and Autolycus
twenty-three. The first named is shallow, only 4,000 feet in depth from
the highest point of its wall, while Aristillus carries some peaks on
its girdle 11,000 feet high. Autolycus, like Cassini, is of no very
great depth.

Westward from the middle of an imaginary line joining Aristillus and
Cassini is the much smaller crater Theaetetus. Outside the walls of this
are a number of craterlets, and a French astronomer, Charbonneaux, of
the Meudon Observatory, reported in December, 1900, that he had
repeatedly observed white clouds appearing and disappearing over one of
these small craters.

Sout