h of the _Mare Vaporum_ are found some of the most notable of those
strange lunar features that are called "clefts" or "rills." Two crater
mountains, in particular, are connected with them, Ariadaeus at the
eastern edge of the _Mare Tranquilitatis_ and Hyginus on the southern
border of the _Mare Vaporum_. These clefts appear to be broad and deep
chasms, like the canons cut by terrestrial rivers, but it can not be
believed that the lunar canons are the work of rivers. They are rather
cracks in the lunar crust, although their bottoms are frequently
visible. The principal cleft from Ariadaeus runs eastward and passes
between two neighboring craters, the southern of which is named
Silberschlag, and is noteworthy for its brightness. The Hyginus cleft is
broader and runs directly through the crater ring of that name.

The observer will find much to interest him in the great, irregular, and
much-broken mountain ring called Julius Caesar, as well as in the ring
mountains, Godin, Agrippa, and Triesnecker. The last named, besides
presenting magnificent shadows when the sunlight falls aslant upon it,
is the center of a complicated system of rills, some of which can be
traced with our five-inch glass.

We next take up Lunar Chart No. 2, and pay a telescopic visit to the
southwestern quarter of the lunar world. The _Mare Tranquilitatis_
merges through straits into two southern extensions, the _Mare
Fecunditatis_ and the _Mare Nectaris_. The great ring mountains or
ringed plains, Langrenus, Vendelinus, Petavius, and Furnerius, all lying
significantly along the same lunar meridian, have already been noticed.
Their linear arrangement and isolated position recall the row of huge
volcanic peaks that runs parallel with the shore of the Pacific Ocean in
Oregon and Washington--Mount Jefferson, Mount Hood, Mount St. Helen's,
Mount Tacoma--but these terrestrial volcanoes, except in elevation, are
mere pins' heads in the comparison.

In the eastern part of the _Mare Fecunditatis_ lies a pair of relatively
small craters named Messier, which possess particular interest because
it has been suspected, though not proved, that a change of form has
occurred in one or other of the pair. Maedler, in the first half of the
nineteenth century, represented the two craters as exactly alike in all
respects. In 1855 Webb discovered that they are not alike in shape, and
that the easternmost one is the larger, and every observer easily sees
that Webb's descri