40 Condition of the Moon's Surface. January, 



rays, falling nearly horizontally, throw the details of this 

 part of the surface into strong relief ; and these appearances 

 suggest this explanation of them. The other ridge answering 

 to a terminal moraine, occurs at the northern extremity of 

 that magnificent valley which runs past the eastern edge of 

 Rheita." 



Here are two lunar features of extreme delicacy, and 

 certainly not incapable of being otherwise explained, re- 

 ferred by Frankland to glacier action. It need hardly be 

 said that glacial action implies the existence of water and 

 an atmosphere on the moon, — and not only so, but there 

 must have been extensive oceans and an atmosphere nearly 

 equal in density to that of our own earth, if the appearances 

 commented upon by Frankland were due to glacial action. 

 It is admitted by Frankland, of course, that there is now no 

 evidence whatever of the presence of water, " but, on the 

 contrary, all selenographical observations tend to prove its 

 absence. Nevertheless," proceeds the account from which I 

 have already quoted, "the idea of former aqueous agency 

 in the moon has received almost universal acceptation " (the 

 italics are mine). " It was entertained by Gruithuisen and 

 others. But, if water at one time existed on the surface of 

 the moon, whither has it disappeared ? If we assume, in 

 accordance with the nebular hypothesis, that the portions 

 of matter composing respectively the earth and the moon 

 once possessed an equally elevated temperature, it almost 

 necessarily follows that the moon, owing to the comparative 

 smallness of her mass, would cool more rapidly than the 

 earth ; for whilst the volume of the moon is only about 

 i-49th (and its mass, it might be added, only about i-8ist 

 part), its surface is nearly i-i3th that of the earth. This 

 cooling of the mass of the moon must, in accordance with 

 all analogy, have been attended with contraction, which 

 can scarcely be conceived as occurring without the develop- 

 ment of a cavernous structure in the interior. Much of 

 this cavernous structure would doubtless communicate, by 

 means of fissures, with the surface ; and thus there would 

 be provided an internal receptacle for the ocean, from the 

 depths of which even the burning sun of the long lunar day 

 would be totally unable to dislodge more than traces of its 

 vapour. Assuming the solid mass of the moon to contract 

 on cooling at the same rate as granite, its refrigeration 

 though only 180 F. would create cellular space equal to 

 nearly 14J millions of cubic miles, which would be more 

 than sufficient to engulf the whole of the lunar oceans, 

 supposing them to bear the same proportion to the mass of 

 the moon as our own oceans bear to that of the earth." 



