EAKTH CHANGES AND EVOLUTION 20i 



sequence of events to which I have called attention an actual 

 reality. 



Terrestrial Temperature Adjustments 



Among the many wonderful adjustments in the human 

 body, and in that of all the higher vertebrates, none perhaps 

 is more complex, more exact, and apparently more difficult 

 of attainment than those which preserve all the circulating 

 fluids and internal organs at one uniform temperature, vary- 

 ing onlj^ four or five degrees Fahr., although it may be ex- 

 posed to temperatures varying more than a hundred degrees. 

 Hardly less wonderful are those cosmical and physical adjust- 

 ments, which, during many millions of years, have preserved 

 the earth's surface within those restricted ranges of temper- 

 ature which are compatible with an ever-increasing develop- 

 ment of animal and vegetable life. 



Equally remarkable, also, is that other set of adjustments 

 leading to those perpetual surface-changes of our globe which 

 I have shown to be the motive power in the development of 

 the marvellously varied world of life; and which has done this 

 without ever once leading to the complete subsidence of any 

 of the great continents during the unceasing motions of ele- 

 vation and depression which have been an essential part of 

 that great cosmic scheme of life-development of which I am 

 now attempting an imperfect exposition. 



That the temperature of the earth's surface should have been 

 kept within such narrow limits as it has been kept during the 

 enormous cycles of ages that have elapsed since the Cambrian 

 period of geology, is the more amazing when we consider that 

 it has always been losing heat by radiation into the intensely 

 cold stellar spaces ; that it has always, and still is, losing heat 

 by volcanoes and hot springs to an enormous extent; and that 

 these losses are only counteracted bv solar radiation and the 

 conservative effect of our moisture-laden atmosphere, which 

 again depends for its chief conservative effect on the enormous 



