51�Թ�

Something more than a hundred miles east-southeast from Menelaus, in the midst of the dark Mare Vaporum, is another brilliant ring mountain which catches the eye, Manilius.

Two crater mountains, in particular, are connected with them, Ariad�us at the eastern edge of the Mare Tranquilitatis and Hyginus on the southern border of the Mare Vaporum.

The counterscarp of the Apennines, in places 160 miles in width from east to west, runs down to the Mare Vaporum with a comparatively gentle inclination.

A portion of it is compared to the river Po, and he traces its course mile by mile up to the "delta" at its place of disemboguement into the Mare Vaporum.

On May 27, 1877, Dr. Hermann Klein of Cologne discovered, with a 5 1/2 inch Plosel dialyte telescope, a dark apparent depression without a rim in the Mare Vaporum, a few miles N.W. of Hyginus, which, from twelve years' acquaintance with the region, he was certain had not been visible during that period.