Page:Popular Science Monthly Volume 10.djvu/587

Rh accessible to most astronomers, and are hence but imperfectly known. The inquiry, we are told, is one of great difficulty, requiring a thorough acquaintance with several branches of science. The results arrived at by prolonged, minute, and careful observation of the details of the lunar formation are rejected because the proofs on which they rest are not well understood.

The most prominent instance of supposed lunar change on the surface of the moon is that of the crater Linné. On the northwest quadrant of the moon, near the centre of a level tract about 430 miles in diameter, there is a bright crater called Bessel, nearly 14 miles in diameter, with a circular wall rising 4,000 feet above the interior, and about 1,600 feet above the surrounding plain. Scattered over this plain are a few small craters, some 2 miles in diameter, with walls about 300 feet high. Near its eastern centre an eminent selenographer named Lohrman placed a distinct, bright crater about five miles in diameter, which he described as being, after Bessel, the most conspicuous object on this great tract of level ground. Ten years later, our greatest selenographer, Baron von Mädler, confirmed Lohrman's observations, and made this crater a subject of special study, naming it Linné. In the drawings of Schmidt, who was about this time making lunar observations of this particular part of the moon, Linné is shown as a deep crater corresponding with the descriptions of Lohrman and Mädler.

In October, 1866, when Linné was in a position to be most conspicuous, Schmidt was startled by finding no trace of the deep, wide crater, but only a faint cloud marking about five miles in diameter. Schmidt at once announced the circumstance, and nearly every astronomer in Europe turned his attention to the spot. But Linné has never since been seen of the size and character given it by Lohrman, Mädler, and Schmidt. This large crater unquestionably no longer exists. Powerful telescopes reveal, in its place, a white, cloudy marking containing a small crater-cone with an opening scarcely one-twentieth the size of the former crater.

The reason why astronomers will not admit the reality of any change in Linné is, first, a strong prejudice against the possibility of such change; and, second, the fact that Schröter, of Lillienthal, the earliest of the great selenographers, in one of his first drawings, made November 5, 1788, with low powers, does not draw Linné as a crater. Near its place he draws a white spot on a ridge marked V, and a larger spot marked G. Schmidt took this white spot to be Linné, a view strongly urged by Huggins, and accepted as correct by astronomers. They say, as Schröter's drawing is not unlike the present appearance of Linné, Lohrman, Mädler, and Schmidt, must have been mistaken as to what they thought they saw. Again, in a map made by Lahire in the seventeenth century, no trace of Linné can be found. It may be said, however, that all the maps of this period