"These latter are formations quite unknown upon our earth, but on the moon they are numbered by hundreds of all sizes, from a few miles up to one hundred and fifty miles in diameter. They are large plains, roughly circular in shape, and surrounded by mountains; in a few cases the ring is in some parts a double range of mountains. Sometimes the plain (or 'floor,' as it is termed) is many thousands of feet below the general level of the lunar surface; in a few cases it is raised considerably above it, and in one or two instances, instead of being flat, the floor is convex. Some of the mountain rings are comparatively low, but in other cases the mountains are fifteen to twenty thousand feet in height, or even higher. Frequently a mountain rises near the centre of the floor, some rings containing more than one such mountain, whilst others have none at all. [Illustration: _Drawn by M. Wicks_ Plate II IDEAL VIEW OF LUNAR SCENERY As there is no atmosphere on the moon, the sky is a dense black, and the stars shine brilliantly in the daytime. The view is a typical one, showing numerous craters and cracks, and a small ring-mountain with terracing. Ring-mountains and plains vary from a few miles to 150 miles diameter, some mountains being nearly 20,000 feet in height.] "There are numerous instances where one mountain ring has overlapped or cut into another, thus indicating that it was a later formation; and in many cases the mountains are 'terraced,'[5] as it is termed, either owing to a series of landslips or to the rise and fall of a sea of lava, which cooled as it sank down, thus forming terraces. Small craters abound all over the surface of the moon and on the floors of the rings; cracks in the lunar surface are also numerous. "As regards the lunar mountains, it may truly be said that we have a fairly accurate knowledge of peaks and mountains which would either be too precipitous to be climbed, or quite inaccessible to us, if we could actually land upon the moon; and the whole visible surface has been more carefully and thoroughly mapped out and studied than is the case with many parts of our own earth. "If the moon has any atmosphere it must be so very attenuated indeed that human beings could not possibly live in it at all; but nothing has yet been detected which would enable us to say positively that any atmosphere does exist there, although there have been some indications observed which support the supposition that there may be an extremely thin air.