GEOLOGICAL SEASONS. 189 







with a thick mantle of snow would be largely expended 

 in the conversion of snow into water. As long as the 

 general covering of snow should remain, no intensity of 

 solar rays could elevate the climatic temperature much 

 above the freezing point of water. The atmosphere in 

 northern regions is nearly diathermanous, and would not 

 be warmed by the passage of the sun's rays; and the heat 

 striking the snow would be converted into mechanical 

 energy instead of accumulating. Little compensation, 

 therefore, could result from the occurrence of summer in 

 perihelion. Observations made upon extensive snow-cov- 

 ered surfaces, as in Greenland, and upon the Antarctic 

 continent, completely confirm these deductions. Moveover, 

 the rapid liquefaction and vaporization of the snow would 

 result, in so cold an atmosphere, in the formation of fogs 

 and clouds, which in turn would, by obstructing the solar 

 rays, react upon their cause. The annual climatic result 

 would, therefore, be a depression of the temperature of 

 the northern hemisphere. The converse of all these con- 

 ditions would exist in the southern hemisphere. Its win- 

 ters would be mild and short, accompanied by but little 

 snowy precipitation, while its summers would be long and 

 comparatively cool. 



At the present time the southern hemisphere is known, 

 from observation, to possess a lower temperature than the 

 northern. The state of things supposed would be more 

 than a reversal of the existing relations of temperature 

 in the two hemispheres. It becomes necessary to inquire, 

 therefore, what would be the effect upon the ocean cur- 

 rents of such a transposition and change of climate; and 

 how would the change in ocean currents react upon cli- 

 mate ? 



