IN THE TELESCOPE. 342. In a telescope of moderate power the moon ceases to show a flat disc, but rounds into a beautiful sphere, which seems to float in the air. Its surface is roughly irregular. Especially about the first quarter, the terminator, or the line which divides the light from the dark part of the disc, is very much broken. Bright spots appear a little beyond the line; in a few hours they unite with the light portion, and are then followed by dark shadows stretching away far from the sunshine. At full moon these strong contrasts vanish, but there is yet a great variety of light and shade. 343. Lunar mountains.-The bright spots are the tops of lunar mountains, gilded by the rising sun. As the slow rotation of the moon brings the mountains farther into sunshine, the light is seen gradually creeping down their sides, and joining that in the valleys below, while shadows are thrown in the opposite direction. These shadows disappear under the vertical sun at full moon, and are cast on the opposite side of the mountains as the moon wanes. The height of the mountains may be estimated from the length of the shadows, or from the distance from the terminator at which the bright top may be seen (16). The highest have an elevation of about 25,000 feet, but little less than that of the highest mountains on the earth. 344. Lunar maps.-Much labor has been expended upon maps of the moon's surface, the most accurate as yet being that of Messrs. Beer and Mädler, 30 inches in diameter. The "Moon Committee" of the British Association have parceled the moon out, and are preparing a map 100 inches in diameter, with all the accuracy of pho tography. The various mountain ranges have been named for ranges on the earth; single peaks and craters for eminent astronomers; level portions, under an old supposition, were called seas and marshes, as Sea of Tranquillity, Sea of Nectar, Ocean of Tempests,-names entirely fanciful. 345. Lunar Craters.-A peculiar feature of the lunar landscape is the great number of rings, walled basins, or craters. These appear to be of volcanic origin, if not the actual craters of volcanoes. Their diameters are very large, 50, 100, and even 133 miles. The walls are steep and ragged, the interior slope often descending much deeper than the exterior. As one of these craters comes into sunshine, the slope opposite the sun is bright with light, while the bottom is dark in the shadow of the wall. A volcanic cone frequently rises from the bottom of a crater. 346. Tycho is a remarkable crater near the southern edge of the moon. In diagrams, which usually show the moon as it appears inverted in a telescope, this mountain appears near the top. Its diameter is about 54 miles; its walls are 16,000 to 17,000 feet high; a mountain rises from the bottom of the crater, about a mile high. The region about Tycho is so completely broken with ridges, peaks, and craters that no level place can be found. Tycho is notable for the great number of streaks of light which diverge from it in every direction, particularly to the north-east. They are so regular that they seem like meridians, and the mountain appears to be the lunar south pole. These bright lines are best seen at the time of full moon; they can hardly be ridges, or they would cast shadows, when the sunlight is oblique to them; they are unlike any thing on the earth, and their nature Other remarkable craters in the north-east, which have a somewhat similar radiated appearance are called Copernicus, Kepler, and Aristarchus. 347. Rilles. These look like huge railway excavations, two parallel slopes on either side of a deep sunken way. They are sometimes a mile and a half wide, from 1300 to 2000 feet deep, and from 10 to 125 miles long. Their dimensions, and the fact that they cut through mountain ridges and craters, show that they can not be river beds. They are probably vast fissures formed in the geological convulsions of the moon. 348. Active volcanoes.-In 1787, Herschel reported three active volcanoes in the moon. In 1794, two persons in different parts of England saw a bright spot, like a star of the third magnitude, upon the dark part of the moon's disc, the moon not having reached her first quarter. As the moon passed before the star Aldebaran on that evening, most astronomers supposed that star to be the spot seen. During lunar eclipses bright spots have been seen, which were thought to be volcanoes. They have been explained as caused by earth-light reflected again from smooth surfaces of rock. IS THE MOON INHABITABLE? 349. Has the moon water?-The gray places were first called seas and marshes, names which now seem inappropriate, as no evidence of water can be found. The sunlight reflected from sheets of water would reveal effects which could be tested by the polariscope (311), but they do not appear. Prof. Mitchel describes a spot which has the appearance of a lake. From mountains which surround it, a sloping beach extends quite to the level surface. The highest magnifying power shows no roughness, and the shading is as regular as if the cavity were filled with ice or quicksilver. "This phenomenon, says Prof. Mitchel, "has baffled the most diligent and persevering efforts to explain." 350. Has the moon air?-The absence of twilight; the absence of refraction, when the light of a star passes near the surface of the moon; and researches with the polariscope, all indicate that the moon has no atmosphere. Without air, the water, if any exists, must be in a state of vapor, as water evaporates in a vacuum; but there is no evidence of even vapor of water. 351. Is the moon inhabited?-Without air and water no form of vegetable or animal life which we know can exist. Even if these conditions were satisfied, the slow rotation of the moon, alternately shutting off the sun's rays, and exposing plants and animals to their unmitigated fierceness for two weeks at once, would require organizations materially different from those found on the earth. May not the rugged nature of the moon's surface show what our earth was in its primitive condition, and would yet be, without the air and water, which have |