224 THE BORDERLAND OF SCIENCE. 



and the moon once possessed an equally elevated tem- 

 perature, it almost necessarily follows that the moon, 

 owing to the comparative smallness of her mass, would 

 cool more rapidly than the earth. This cooling of the 

 moon's mass must, in accordance with all analogy, have 

 been attended with contraction, which can scarcely be 

 conceived as occurring without the development of a 

 cavernous structure in the interior. Much of the 

 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 through only 180 

 degrees of the Fahrenheit thermometer (the difference 

 between the boiling heat and the freezing point) would 

 create cellular space equal to nearly 14 J 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.' 



Room might certainly be found in this way for all 

 the lunar oceans, because the moon's surface amounts 

 only to 14,600,000 square miles, and therefore the 

 cellular space deduced above amounts to the volume of 

 an ocean competent to cover the whole surface of the 

 moon to the depth of a mile. But then, where has 

 the lunar atmosphere gone to ? It would require 



