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Even with the naked eye we see on its 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 crust is pierced by craters, whose irregu. lar edges and rents testify to the convulsions ou satellite has undergone at some past time.
Mountains.—The heights of more than 1,000 of these lunar mountains have been measured, some of which exceed 20,000 feet. The shadows of the mountains, as the sun's rays strike them obliquely,
are as distinctly perceived as that of an upright • staff when placed opposite the sun. Some of these
are insulated peaks that shoot up solitary and alone from the centre of circular plains; others are mountain ranges extending hundreds of miles. Most of the lunar elevations have received names of men distinguished in science. Thus we find Plato, Aristarchus, Copernicus, Kepler, 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 have more recently been found to ex
* Several distinguished astronomers assert, however, that the crater Linnæus has undergone of late certain marked changes. 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.
hibit the uneven appearances of a plain, instead of the regular curve of bodies of water. 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 radi. ate 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 exact nature is yet a mystery.
Craters. These constitute by far 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 centre. Some of the craters have a diameter of over 100 miles. They are great walled plains, sunk so far behind huge volcanic ramparts, that the lofty wall which surrounds an observer at the centre 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 of the region to the southeast of Tycho. (Fig 46.)