Page:Astronomy for Everybody.djvu/149

scope the more details we see. The first thing to strike us on a telescopic examination will be the elevations, or mountains as they are commonly called. These are best seen about the time of the first quarter, because they then cast shadows. At full moon they cannot be so well made out, because we are looking straight down and see everything illuminated. Although these elevations and depressions are called mountains they are different in form from the ordinary mountains of the earth. There is, however, an almost exact resemblance between them and the craters of our great volcanoes. A very common form is that of a circular fort, one or more miles in diameter, with walls which may be thousands of feet high. The inside of this fort may be saucer shaped, a large portion of the surface being flat. At first quarter we can see the shadow of the walls cast upon the interior flat surface. In the centre a little cone is frequently seen. The interior surface is by no means perfectly flat and smooth. The higher power the more details we shall see. Just what these consist of it is impossible to say; they may be solid rock or they may be piles of loose stone. As we can see no object on the moon, even with the most powerful telescope, unless it is more than a hundred feet in diameter, we cannot say what the exact nature of the surface is in its minutest portions.

The early observers with the telescope supposed that the dark portions were seas and the brighter portions continents. This notion was founded on the fact that the darker portions looked smoother than the others. Names were therefore given to these supposed oceans, such