NEWS FROM THE MOON. 219 



form of rain or snow or stream or flood, or else to pro- 

 cesses such as vegetation or the succession of various 

 forms of animal life. In the moon, so far as can "be 

 judged, we see the natural skeleton, as it were, of a 

 planet, the rock surface precisely as it was left when 

 the internal forces ceased to act with energy. There 

 has been no ' weathering ;' no wearing down of the sur^ 

 face by the action of water; no forests have formed 

 carboniferous layers; no strata like our chalk forma- 

 tions have been deposited; vegetation does not hide 

 any part of the surface; no snows have fallen, and 

 therefore no glaciers grind clown the rugged surface of 

 the lunar valleys. With one exception, there is not, so 

 far as can be judged, any process which is at work to 

 disintegrate or modify the sterile face of the moon* 

 The exception is the process of alternate expansion and 

 contraction of the moon's crust, as the lunar day and 

 night pass on in slow succession. Unquestionably, the 

 change from a heat of some five hundred degrees at 

 midday, to a cold far more intense than any with which 

 we are acquainted on earth, must cause a gradual 

 change in portions of the moon's surface. 



But we are thus led to a most interesting question 

 respecting the moon. It is manifest that now, at any 

 rate, there is no water and very little air (if any) on 

 the half of the moon turned towards us. Yet it is 

 argued that those volcanic disturbances which are indi- 

 cated so strikingly by the moon's aspect, imply the 

 former existence both of water and of air. On our earth 

 water appears absolutely necessary for the occurrence of 



