ioo, ROUGH WAYS MADE SMOOTH. 



moon ; and, secondly, that the moon's crust must possess a 

 life of its own, so to speak, expanding and contracting un- 

 ceasingly and energetically. Professor Newcomb, by the 

 way, in his fine work on Popular Astronomy, rejects the idea 

 that the expansions and contractions due to these great 

 changes of temperature can cause any disintegration at the 

 present time. There might, he says, be bodies so friable 

 that they would crumble, 'but whatever crumbling might 

 thus be caused would soon be done with, and then no further 

 change would occur.' For my own part, I cannot consider 

 that such a surface as the moon at present possesses can 

 undergo these continual expansions and contractions without 

 slow disintegration. It seems to me also extremely probable 

 that from time to time the overthrow of great masses, the 

 breaking up of arched crater-floors, and other sudden changes 

 discernible from the earth, might be expected to occur. 

 Professor Newcomb has, I conceive, omitted to consider the 

 enormous volumetric expansion as distinguished from mere 

 lateral extension, resulting from the heating of the moon's 

 crust to considerable depths. On a very moderate com- 

 putation, the surface of the central region of the full moon 

 must at that time rise above its mean position to such a 

 degree that hundreds, if not thousands, of cubic miles of the 

 moon's volume lie above the mean position of the surface 

 there. At new moon that is, at lunar midnight for the 

 same region the same enormous quantity of matter is cor- 

 respondingly depressed. And though the actual range in 

 vertical height at any given point may be small, we cannot 

 doubt that the total effect produced by these constant oscil- 

 lations is considerable. Years or centuries may pass without 

 any great or sudden change, but from time to time such 

 catastrophes must surely occur. I believe that all the 

 cases of supposed change in the moon, if all were regarded 

 as proved, could be thus fully accounted for without any 

 occasion to assume the action of volcanic forces properly so 

 called. 



Before considering the evidence for the new lunar 



