332 COSMIC PUILOSOPll V. [pt. 11. 



driven back towards the surface. Tn this way there is kept 

 up a circulation of water through the peripheral portions of 

 the earth's crust. But as the earth becomes cooler and cooler, 

 the water will be enabled to circulate at greater and greater 

 depths, thus materially lowering the level of the ocean. In 

 this way, long before the centre has become cool, all the 

 surface-water of the earth will have been sucked into the 

 pores of the rocks, and a similar process will afterwards take 

 place with the atmosphere. M. Saemann shows that by the 

 time the earth had reached complete refrigeration, the pores 

 of the rocks would absorb more than one hundred times the 

 amount of all the oceans on the globe, while room would still 

 be left for the retiring atmosphere. Now this state of 

 things, which will no doubt by and by be realized on the 

 earth, would seem to be already realized on the moon. 

 Being forty-nine times smaller than the earth, the moon has 

 cooled with great rapidity, and its geologic epochs have been 

 correspondingly short. 1 



After the moon, we are more familiar with the surface of 

 Mars than with that of any other heavenly body, the posi- 

 tion of Yenus being very unfavourable for thorough observa- 

 tions. Concerning the physical geography and meteorology of 

 Mars, some trustworthy information has been obtained. The 

 distribution of land and sea over his surface is sufficiently 

 obvious to be delineated in maps. He possesses liquid oceans, 

 proved by spectroscopic evidence to consist of water, an:l 

 his atmosphere is gaseous. That he possesses climates analog- 

 ous to our own might be inferred from the inclination of his 

 axis to his orbit-plane, and is inductively proved by the fact 

 that we can actually see his polar snows accumulate during 

 the Martial winter and melt away at the approach of the 



1 It should be added that the rapid cooling of the moon would greatly 

 increase the porosity of its substance. Prof. Frankland has shown that 

 "assuming the solid mass of the moon to contract on cooling at the same 

 rate as granite, its refrigeration through only 180° F. would create cellular 

 space eyual to nearly fourteen and a half millions of cubic miles." 



