FAILURE OF CLIMATIC THEORIES. 3 



Others, again, tried to explain the great changes of 

 climate by supposing, with M. Poisson, that the earth 

 during its past geological history may have passed 

 through hotter and colder parts of space. This theory, 

 however, was found to be so much opposed to known 

 physical principles that it soon had to be abandoned. 



It has also been suggested that the changes of 

 climate during geological ages might have resulted 

 from alternations in the composition of the atmosphere, 

 particularly in variations in the amount of carbonic 

 acid gas possessed by the air. 



A theory was advanced many years ago by Professor 

 H. Le Coq that the changes of climate may have been 

 due to changes in the amount of the sun's heat. But 

 this theory, like the above, appears to have gained but 

 little acceptance. 



According to others, elevation of the land in the 

 regions glaciated is assigned as the cause of that 

 glaciation, and if the ice had been merely local, such 

 an explanation might have sufficed. But we know 

 the whole Northern Hemisphere, down to tolerably 

 low latitudes, has been subjected in post-tertiary times 

 to the rigour of an Arctic climate ; so that, according 

 to this theory, we must assume an upheaval of the 

 entire hemisphere — an assumption too monstrous to 

 be admitted, and as useless as absurd. 



At one time Lyell's theory of the relative distribu- 

 tion of land and water was generally regarded by 

 geologists as sufficient. It is, however, now generally 

 admitted to be wholly insufficient to explain the now- 

 known facts, and the conviction is becoming almost 

 universal that we must refer the climatic changes in 

 question to some cosmical cause. 



The theory of a change in the obliquity of the 

 ecliptic has been appealed to. This theory for a time 



