A NEW CRATER IN THE MOON. 107 



lieve that some of the multitudinous small craters of the 

 moon have had their origin in the downfal 1 of meteoric masses 

 on her once plastic surface ; and strange though the thought 

 may seem, there would be considerable difficulty in showing 

 how the surface of the moon could have remained without 

 traces of the meteoric downfall to which during myriads of 

 centuries she was exposed undefended by that atmospheric 

 shield which protects our earth from millions of meteors yearly 

 falling upon her. We could only attribute the smallest lunar 

 craters, however, to this cause. It may be noticed in passing 

 that Professor Newcomb, apparently referring to this sugges- 

 tion, which some had thought too fanciful to be seriously 

 advanced, says that ' the figures of these inequalities (the 

 small craters) can be closely imitated by throwing pebbles 

 upon the surface of some smooth plastic mass, as mud 

 or mortar.' Craters, however, larger than a mile or so in 

 diameter, and many also of smaller dimensions, must be re- 

 garded as due to the same process of contraction which pro- 

 duced the great craters, but as belonging to an era when 

 this process went on less actively. In like manner another 

 feature of the moon's surface, the existence of narrow furrows 

 called rilles, which sometimes extend to a considerable dis- 

 tance, passing across levels, intersecting crater walls, and 

 reappearing beyond mountain-ranges as though carried under 

 like tunnels, must be regarded as due to the cracking of the 

 crust thus slowly shrinking. 



It is noteworthy that the signs of change which have 

 been suspected during recent years belong to these smaller 

 and probably more recent lunar formations. In November, 

 1866, Dr. Schmidt, chief of the Athens Observatory, an- 

 nounced that the crater Linne in the lunar. Sea of Serenity 

 was missing. To understand the importance of this an- 

 nouncement, let it simply be noted that the quantity of 

 matter necessary to fill that crater up would be at least 

 equal to that which would be required to form a 

 mountain covering the whole area of London to a height 

 of two miles ! The crater was described by former lunar 



