26 DISCUSSIONS IN CLIMATOLOGY. 



ation ; and although the heat lost by expansion is fully 

 restored by compression, yet the air would reach the 

 earth deprived almost entirely of the heat with which 

 it left the equator. All that it could possibly give 

 back would simply be the heat of compression ; and 

 this would hardly be sufficient to raise the air at 

 — 50° F. to the freezing-point. How then can the 

 polar regions be greatly the better of air from the 

 equatorial regions ? Professor Newcomb says : — " If 

 the upper current be as great as is commonly supposed, 

 it must be as powerful as ocean-currents in tending to 

 equalise the temperature of the globe." How can this 

 be? 



Why the Mean Temperature of the Ocean should 

 be greater than that of the Land. — " Another proposi- 

 tion," he says, "which the author attempts to prove, 

 reasoning which seems equally inconclusive, is that 

 the mean temperature of the ocean is greater than 

 that of the land over the entire globe." I certainly 

 never attempted to prove that the mean temperature 

 of the ocean is greater than that of the land over the 

 entire globe. The very chapter to which he here 

 refers, and which he is about to criticise, was written 

 to explain why the mean temperature of the southern 

 or -water hemisphere is less than that of the northern 

 or land hemisphere. What I attempted to prove was, 

 not that the mean temperature of the ocean is greater 

 than that of the land, but that, were it not for certain 

 causes, the mean temperature of the ocean ought to 

 be greater than that of the land in equatorial regions 

 as well as in temperate and arctic regions. In other 

 words, the object of the chapter was to prove that the 

 mean temperature of the southern or water hemisphere 

 was less than that of the northern or land hemisphere, 

 not, as was generally supposed, because the former is 



