276 



CLIMATE OF THE EAETH AFFECTED 



[Ch. XIII. 



received from the sun but by T V th, because the heat vanes in- 

 versely as the squares of the distance. Yet, as if in violation 

 of this law, when the temperatures of all places north and 

 south of the line are reduced to an average, it is found that the 

 surface of the whole planet is actually warmer in June than 

 in December, i.e., in aphelion than in perihelion. This result, 

 which in an astronomical point of view appears so paradoxical, 

 is explained in a satisfactory manner when we take into con- 

 sideration the great extent of land which exists between the 

 equator and the 50th degree of north latitude, and which is 

 exposed to the sun's rays during a long summer, whereas the 

 extent of ocean in corresponding latitudes in the southern 



m. /"^ *^ ft "^ A 



mi 



estimate 



summer, notwithstanding that here, according to Herschel's 



the power of the sun is greater by 23° F. when the 

 planet is in perihelion. < The effect of land,' says Herschel, 

 < under sunshine is to throw heat into the general atmo- 

 sphere, and so distribute it by the carrying power of the air 

 over the whole earth. Water is much less effective in this 

 respect, the heat penetrating its depths and being there 

 absorbed, so that the surface never acquires a very elevated 

 temperature, even under the equator.'* 



The present effect, therefore, of the excentricity of the 

 orbit on climate is so subordinate to that of the position of 

 the land, that it is not only nullified by it, but the result is 



mi 



Another illustration of the counteracting effect of geo- 

 graphical causes is afforded by the extreme climates of 

 Canada and other parts of North America, as well as of cer- 

 tain parts of Siberia and China, as contrasted with the more 

 eauable climates of the southern hemisphere. A very dif~ 



miarht 



& 



com 



summer 



om 



most 



compared to land produces an equable or what is called an 



insular' climate. 



* Herschel's Astronomy, 1864, p. 236, art. 376- 



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