In Beer and Mädler’s chart of the Moon the names are attached to the various formations, as they are also in Neison’s maps and in some other works. One of these will be absolutely necessary to the student in prosecuting his studies. He will then have a ready means of acquainting himself with the various formations, and making comparisons between his new results and the drawings of earlier selenographers. I would refer the reader to Neison’s and Webb’s books for many references in detail to lunar features, and must be content here with a brief description of a few leading objects:— _Plato_ is an extensive walled plain, 60 miles in diameter, and situated on the N.E. boundary of the Mare Imbrium. Nasmyth and Carpenter describe the wall as “serrated with noble peaks, which cast their black shadows across the plateau in a most picturesque manner, like the towers and spires of a great cathedral.” It has received a large amount of attention, with a view to trace whether changes are occurring in the numerous white spots and streaks lying in its interior. In 1869-71 Mr. Birt collected many observations, and on discussing them was led to believe that “there is strong probability that activity, of a character sufficient to render its effects visible, had been manifested.” The inquiry was renewed by Stanley Williams in 1882-84, and he concluded that the results were strongly confirmatory of actual change having occurred since 1869-71. The relative visibility of several of the bright spots had altered in the interim, and the curious intermingling bright streaks also exhibited traces of variation. At sunrise the interior of Plato is pure grey; but with the sun at a considerable height above it, the plain becomes a dark steel-grey. The change is an abnormal one, and difficult to explain. South of Plato there is a fine example of an isolated peak, named Pico, which is about 8000 feet high. [Illustration: Fig. 25. Light-spots and streaks on Plato, 1879-82. (A. Stanley Williams.)]