How strange the lunar appearance would be to us! The disk of the sun seems sharp and distinct. The sky is black and overspread with stars even at midday. There is no twilight, for the sun bursts instantly into day, and, after a fortnight's glare, as suddenly gives place to night; no air to conduct sound; no clouds; no winds; no rainbow; no blue sky; no gorgeous tinting of the heavens at sunrise and sunset; no delicate shading; no soft blending of colors, but only sharp outlines of sun and shade.*

The nights of the visible hemisphere must be brilliantly illuminated by the earth, whose phases "serve well as a clock-a dial all but fixed in the same part of the heavens, like an immense lamp, behind which the stars slowly defile along the black sky."

Telescopic Features.-Even with the naked eye, we see on the moon's surface bright spots (the summits of lofty mountains, gilded by the first rays of the sun), and darker portions-low plains yet lying in comparative shadow. The telescope reveals to us a region torn and shattered by fearful though now extinct volcanic action.

Everywhere the

The moon is a fossil world, an ancient cinder, a ruined habitation perpetuated only to admonish the earth of her own impending fate, and to teach her occupants that another home must be provided, which frost and decay can never invade. The moon was once the seat of all the varied and intense activities that now characterize the surface of our earth. At one time its physical condition was like that of the parent earth from which it had just been separated: but, being smaller, it cooled faster, and its geologic periods were correspondingly shorter. Its life-age was perhaps reached while the earth was yet glowing.-Read Winchell's Geology of the Stars.

+ Several distinguished astronomers assert, however, that the crater Linnæus has undergone noticeable transformations. Its sides seem to have fallen in, and the interior to have become filled up, as if by a new eruption. It is said to present an appearance similar to that of the Sea of Serenity. Other marked changes are said to have been discovered from time to time, on the moon's surface, but they are not generally ac

crust is pierced by craters, whose irregular edges and rents testify to the convulsions our satellite has undergone.

MOUNTAINS.-The heights of more than 1,000 of the lunar mountains have been measured, some of which exceed 25,000 feet. When the sun's rays strike one of these mountains obliquely, the shadow is as distinctly perceived as that of an upright staff when placed opposite the sun. Some of the elevations are insulated peaks that shoot up from the center of circular plains; others are mountain ranges extend

ing hundreds of miles. Most of the lunar heights have received names of men distinguished in science. Thus we find Plato, Aristarchus, Copernicus,* Kepler,

credited. For an interesting discussion of this subject, read a chapter entitled "A New Crater in the Moon," in Proctor's Poetry of Astronomy.

*This is one of the grandest of the lunar craters. It is situated on the tip of the nose of the "Man in the Moon." Its diameter is forty-six miles, and its encircling rampart rises 12,000 feet above the interior plateau, in the midst of which stands a group of cones, one 2,400 feet in height.

and Newton, associated, however, with the Apennines, Carpathians, etc.

GRAY PLAINS, OR SEAS.-These are analogous to our prairies. They were formerly supposed to be sheets of water, but they exhibit the uneven appearance of a plain, instead of the regular curve of a sea. The former names have been retained, and we find on lunar maps the Sea of Tranquillity, the Sea of Nectar, Sea of Serenity, etc.

RILLS, LUMINOUS BANDS. -The latter are long, bright streaks, irregular in outline and extent, which radiate in every direction from Tycho, Kepler, and other mountains; the former are similar, but are sunken, and have sloping sides, and were at first thought to be ancient river-beds. Their nature is a mystery.

CRATERS Constitute the most curious feature of the lunar landscape. They are of volcanic origin, and usually consist of a cup-like basin, with a conical elevation in the center. Some of the craters have a diameter of over 100 miles, and are great walled plains, sunk so far behind huge, volcanic ramparts that the lofty wall surrounding an observer at the center would be beyond his horizon. Other craters are deep and narrow,-as Newton, which is said to be about four miles in depth,-so that neither earth nor sun is ever visible from a great part of the bottom. The appearance of these craters is strikingly shown in the accompanying view (Fig. 53) of the region to the southeast of Tycho.