162 LIFE ON THE EARTH. 



as our problem seems to require. "What are the ob- 

 jections to it? 



Two, principally. First. The rate of increase of 

 temperature, as we go downward, is proportioned to 

 the quantity of heat flowing out and influencing the 

 climate by increase of sensible or thermometric tem- 

 perature. To augment by 10, 20, or 30 the existing 

 temperature of the surface would require an aug- 

 mentation of heat from the surface downward, in 

 the same proportion as the measure of warmth to 

 be communicated (say 10) to the measure of warmth 

 (say gV^h of a degree) actually communicated. In 

 the case supposed, 200 times as great as now, the 

 heat of boiling water would be attained at about 50 

 feet of depth ! How under such circumstances could 

 the Mollusca and other creatures live in the sea, or 

 plants grow on the land? 



Secondly. The rate of cooling of the earth by 

 radiation into space is so slow at present, that to 

 reduce the actual effect (say gVth of a degree) to 

 half that amount would require, according to the 

 calculation of Poisson, the period of one hundred 

 thousand millions of years 1 . In earlier times, the 

 flow of heat outward being much greater, the rate 

 of cooling would have been much more rapid; still 

 the period of time which must have elapsed in the 



1 Hopkins, Address to Geol Soc. 1851. 



