Dr. Croll's Theory of Glacial and Warm Periods. 83 



between the equator and the north pole is not the same, 

 but greater than the difference between the respective tem- 

 peratures of the equator and the south pole. Inter alia, he 

 says : " As the existence of the winds depends mainly on 

 the difference of temperature between equatorial and polar 

 regions, any cause which will greatly affect this difference 

 of temperature will likewise greatly affect the winds." He 

 argues that an increase or decrease in the difference of tem- 

 perature between equatorial and polar regions would produce 

 an increase or decrease in the strength of the winds, and 

 consequently in the strength of the currents, and that a 

 difference in the difference of temperature between the 

 equator and the two poles would affect the distribution of 

 aerial and consequently of ocean currents, and would in 

 turn produce a corresponding increase in the difference of 

 temperature between the two hemispheres. This change, 

 again, would tend to strengthen one trade wind and to 

 weaken the other," etc., etc. 



I cannot agree with this conclusion, which is at issue 

 both with a priori and with empirical tests. 



The chief condenser and refrigerator, where the warm 

 damp air of the torrid zone is deprived of its heat and 

 moisture, is not the area at each pole but the upper region 

 of the atmosphere. 



As we have shewn elsewhere, the warm current which 

 rises at the equator, rises at least higher than the peaks of 

 the Andes, that is far above the snow-line, and into a region 

 which but for this current would be perpetually below 32 

 in temperature, and it remains in the cold region during the 

 greater part of its journey to the two tropics. 



It does not matter, therefore, how cold the poles are 

 made, they cannot drag or pull this equatorial current of 

 air towards them. It has much closer at hand, namely, 

 in the regions of space, a much colder refrigerator than 

 either pole, which must inevitably cool it down and deprive 



