158 DISCUSSIONS IN CLIMATOLOGY. 



sphere which prevailed during Cretaceous, Eocene, 

 and Miocene times,* it might indirectly affect it by- 

 increasing the mass of Antarctic ice, and thus increas- 

 ing the force of the trade -winds and the resulting 

 northward-flowing warm currents. . . . And as we 

 have seen that during the last three million years the 

 eccentricity has been almost always much higher than 

 it is now, we should expect that the quantity of ice in 

 the southern hemisphere will usually have been greater, 

 and will thus have tended to increase the force of those 

 oceanic currents which produce the mild climates of 

 the northern hemisphere." "f - 



There is little doubt but that the climate of the 

 Tertiary period was greatly affected by eccentricity ; 

 but, owing to the difference in the geographical 

 conditions of the two hemispheres, eccentricity would 

 exercise a much greater influence on the climatic 

 condition of the northern hemisphere when the 

 northern winter solstice was in perihelion than it 

 would do when it was in aphelion. Owing to the 

 difference in the conditions of the two hemispheres, 

 the physical agents brought into operation by a high 

 state of eccentricity would act more powerfully in 

 impelling the equatorial waters towards the Arctic 

 regions when the winter solstice was in perihelion 

 than they would do in impelling the water towards 

 the Antarctic regions when the solstice was in 

 aphelion. In this case the northern hemisphere 

 would be heated to a greater extent when its winter 

 solstice was in perihelion than it would be cooled 

 when the solstice was in aphelion. It is this circum- 



* High eccentricity might not directly modify the mild climates, 

 but certainly the physical agents brought into operation by the high 

 eccentricity would do so. 



f " Island Life," p. 192. 



