“You will also observe that the afternoon slant of the solar rays has considerably changed the appearance of Aristarchus. Now for the first time the crateriform shape of that most remarkable mountain has become evident on account of the shadow in the interior. This shadow has almost reached the central peak which is the brightest part of the entire formation. You may be interested in the fact that the brilliance of the central peak of Aristarchus is so great that it stands in an order by itself, in what may be called the photometry of the moon’s surface. Ten orders of relative brightness have been adopted to represent the various reflective powers of different parts and spots of the moon. I copy them from Mr. Elger’s list. They are as follows: “0° = Black (example, the shadows of mountains). “1° = Gray black (example, darkest places in the walled plains of Grimaldi and Riccioli). “2° = Dark gray (example, the floor of Endymion). “3° = Medium gray (example, interior of Theophilus). “4° = Yellowish gray (example, interior of Manilius). “5° = Pure light gray (example, surface around Kepler). “6° = Light whitish gray (example, walls of Macrobius). “7° = Grayish white (example, Kepler). “8° = Pure white (example, walls of Copernicus). “9° = Glittering white (example, Proclus). “10° = Dazzling white (sole example, the central peak of Aristarchus).” “Really, I am greatly surprised by what you tell me,” said my friend. “I would never have imagined that there were so many different neutral tints on the moon.” “You would be still more surprised,” I replied, “if I could present to you a similar table of the different tints of color that have been discovered there. But I am not aware that any scale of lunar colors has been prepared. There are, however, various shades of brown, yellow, and green. Most of them are found in the _mares_ and walled inclosures. Some of them appear to be variable, and some are only to be detected under particular illuminations.” “Are not such colors an indication of something living there?” “It may be so—an indication, for instance, of the existence of ‘lunar grass,’ the mention of which so amused you a little while ago.”