Ch. XIII.] 



BY GEOGRAPHICAL CAUSES 



277 



The fact that the cold is now greater throughout a large part 



seem at first sight almost 



demonstrate 



of the winter solstice with aphelion exerts a powerful refri- 



aerating: effect- Bnt tr 

 perate latitudes in the 



hemisph 



tem 

 shown by 



Dove's tables to be due to a deficiency of land, which is in 

 excess in corresponding latitudes of the northern hemisphere. 

 Without denying that the astronomical cause alluded to 



must exercise some 



contrasted with the power of geographical conditions. 



Sir 



Herschel, indeed, com 



there ought to be a difference of 23° F. when two places are 



com 



summer 



opposite sides of the equator ; that is to say, tiie 

 coinciding with perihelion ought to have a temperature of 

 1U° higher, and the winter in aphelion a temperature lower 



same 



astronomical 



The results of observation are not in harmony with this theory, 

 the difference really indicated by the thermometer being only 

 half that which is required by theory. Yet there are some 



Herschel 



makes 

 tralia is 



The heat, he says, in the interior of Aus- 



greater 



than in the deserts 



North 



corresponding latitudes ; and he has himself observed the 

 temperature of the surface soil in South Africa to reach 

 159° F., which is higher than it ever rises in our hemisphere 



i „~+ ^1-nnAa wi+Ii -nA-rihelion.* TJnfor- 



summer 



astronomical and meteorolo 



servation is too short to enable us to calculate the changes of 

 temperature to which precession gives rise under the present 

 conditions of excentricity . 



M. Adhemar 



Les Eevolutions de la 



Mer 



already resulted from the deviation which has occurred since 



from the time 



of the winter solstice in the north. 



m 



* HerscheVs Astronomy, 1864, art. 369, note. 



