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. South 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.