foS ROUGH WAYS MADE SMOOTH. 



observers as at least five miles in diameter and very deep. 

 It is not now actually missing, as Schmidt supposed, 

 but it is certainly no longer deep. It is, in fact, exceedingly 

 shallow. Sir J. Herschel's opinion was that the crater had 

 been filled up from beneath by an effusion of viscous lava, 

 which, overflowing the rim on all sides, poured down the 

 outer slope so as to efface its ruggedness and convert it into 

 a gradual declivity casting no stray shadows. But the 

 stupendous nature of the disturbing forces necessary to 

 produce such an overflow of molten matter has led most 

 astronomers to adopt in preference the theory that the wall 

 surrounding the crater has been overthrown, either in con- 

 sequence solely of the processes of contraction and expan- 

 sion described above, or from the reinforcement of their 

 action by the effects due to sublunarian energies. Some 

 consider that the descriptions of the crater by Madler and 

 Lohrmann (which slightly differ) were erroneous, and that 

 there has been no real change. Others deny that any 

 change has occurred, on the ground that Linne varies in 

 aspect according to the manner of its illumination. This I 

 perceive is Professor Newcomb's explanation, who considers 

 such variations c sufficient to account for the supposed 

 change.' But since the time of Schmidt's announcement 

 Linne has several times been observed under nearly the 

 same conditions as by Madler and Lohrmann, as the great 

 shadows formerly seen in its interior have not reappeared. 

 There seems to be great reason for believing that a change 

 has really occurred there. 



The discovery announced by Dr. Klein is of a dif- 

 ferent nature. Near the middle of the visible half of the 

 moon there is a well-known though small crater called 

 Hyginus, the neighbourhood of which has been often and 

 carefully examined. While examining this part of the 

 moon's surface with an excellent 5^in. telescope, in May, 

 1677, Dr. Klein observed a small crater full of shadow, and 

 apparently nearly three miles in diameter, It formed a con- 

 spicuous object on the Sea of Vapours. Having frequently 



