are Nubium_, is a very conspicuous and
beautiful ring mountain about thirty-eight miles in diameter, with walls
8,000 feet high above the interior.

Those who wish to see the lunar mountains in all their varying aspects
will not content themselves with views obtained during the advance of
the sunlight from west to east, between "new moon" and "full moon," but
will continue their observations during the retreat of the sunlight from
east to west, after the full phase is passed.

It is evident that the hemisphere of the moon which is forever turned
away from the earth is quite as marvelous in its features as the part
that we see. It will be noticed that the entire circle of the moon's
limb, with insignificant interruptions, is mountainous. Possibly the
invisible side of our satellite contains yet grander peaks and crater
mountains than any that our telescopes can reach. This probability is
increased by the fact that the loftiest known mountain on the moon is
never seen except in silhouette. It is a member of a great chain that
breaks the lunar limb west of the south pole, and that is called the
Leibnitz Mountains. The particular peak referred to is said by some
authorities to exceed 30,000 feet in height. Other great ranges seen
only in profile are the Doerfel Mountains on the limb behind the ring
plain Bailly, the Cordilleras, east of Eichstadt, and the D'Alembert
Mountains beyond Grimaldi. The profile of these great mountains is
particularly fine when they are seen during an eclipse of the sun. Then,
with the disk of the sun for a background, they stand out with startling
distinctness.

THE SUN

When the sun is covered with spots it becomes a most interesting object
for telescopic study. Every amateur's telescope should be provided with
apparatus for viewing the sun. A dark shade glass is not sufficient and
not safe. What is known as a solar prism, consisting of two solid prisms
of glass, cemented together in a brass box which carries a short tube
for the eyepiece, and reflecting an image of the sun from their plane of
junction--while the major remnant of light and heat passes directly
through them and escapes from an opening provided for the
purpose--serves very well. Better and more costly is an apparatus called
a helioscope, constructed on the principle of polarization and provided
with prisms and reflectors which enable the observer, by proper
adjustment, to govern very exactly and delicately the amount of ligh