57 o THE POPULAR SCIENCE MONTHLY. 



omit numerous craters far larger than Linne. They were principally 

 full-moon drawings, where Linne would not be visible as a crater. 

 Kiccioli's map, however, shows Linne as a distinct crater. But the 

 present crater on the site of Linne 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 

 Schroter, and Beer, and Madler, Schroter's are rejected, while in this 

 particular case one of Schroter's earliest drawings, made with imper- 

 fect 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 Linne. From 

 numerous observations the explanation agreeing best with the present 

 condition of the surface is, that the walls of the old crater have col- 

 lapsed 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 im- 

 mediately 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 con- 

 ditions. 



Proctor has tried to show that the changes in Linnu are variations 

 of tint due to differences of illumination. But no selenographer will 

 admit that any alteration whatever in illumination could make an ob- 

 ject where Linne is placed, look at one period like a considerable and 

 deep crater, and at another as a small, scarcely visible crater. 



The facts about Linne may be therefore summed uj) very briefly. 

 According to three or more independent selenographers, the most ex- 

 pei'ienced that science has seen, the object named Linne was a con- 

 spicuous 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 de- 

 scription 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 sur- 

 face 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 



