Page:Popular Science Monthly Volume 10.djvu/588

570 omit numerous craters far larger than Linné. They were principally full-moon drawings, where Linné would not be visible as a crater. Riccioli's map, however, shows Linné as a distinct crater. But the present crater on the site of Linné could not possibly have been seen by Riccioli with the optical means at his command.

In every other instance of discrepancy between the drawings of Schröter, and Beer, and Mädler, Schröter's are rejected, while in this particular case one of Schröter's earliest drawings, made with imperfect instruments, is brought forward to prove the incorrectness of his great successors.

It will require long study of this region with powerful telescopes to determine the nature of the change undergone by Linné. From numerous observations the explanation agreeing best with the present condition of the surface is, that the walls of the old crater have collapsed and fallen into the interior. In this way the interior would be almost entirely filled up, leaving a rough, cone-like crater in the centre. Under favorable conditions, with a powerful telescope, the surface immediately around the small crater appears rough and irregular. Round the border of the old crater are numerous mounds and blocks, and on the east, one or two peaks or low hills, seeming like portions of the old wall. The difficulty of making these observations is very great, and they are only possible in the finest atmospheric conditions.

Proctor has tried to show that the changes in Linné are variations of tint due to differences of illumination. But no selenographer will admit that any alteration whatever in illumination could make an object where Linné is placed, look at one period like a considerable and deep crater, and at another as a small, scarcely visible crater.

The facts about Linné may be therefore summed up very briefly. According to three or more independent selenographers, the most experienced that science has seen, the object named Linné was a conspicuous crater of large diameter and great depth. Now, in its place all that exists is a tract of uneven ground, containing a small, scarcely visible, insignificant, crater-like object, It is impossible that one could ever be systematically taken for the other. It is inconceivable how our three greatest selenographers could have systematically and independently made the same blunder, and that one blunder only. For in no other case do we find any error of this nature. Their description must, therefore, be held to truly describe the nature of the formation at their epoch (1820-'45). The object is no longer of the same size and description. A real physical change on the moon's surface must therefore have occurred at this point. This, then, is the conclusion that selenographers as a body have arrived at; yet, despite the strong evidence on which it rests, it is not generally recognized by astronomers.

The next instance of change on the surface of the moon is that of