*n 



Ch. XII.] 



CUEEENTS EQUALISE TEMPERATURE. 



243 



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inhabits, and where he has even built ports and inland 



villages. 



The chief causes of the intense cold of high southern 



latitudes are twofold : first, the vast height and extent of 



the antarctic continent ; and secondly, what is no less im- 



portant, 



the almost entire absence of land in the South 

 ta Zone, where its presence would warm the atmo* 



some 



sphere. It may undoubtedly be said, that 

 cold of south polar latitudes is due to the present condition 

 of the southern hemisphere in regard to the precession of 

 the equinoxes, and the excentricity of the earth's orbit. For 

 its winters occur when the earth is at its greatest distance 

 from the sun, and they are eight days longer than the winters 

 of the northern hemisphere. That this cause is not without its 

 effect in somewhat augmenting the quantity of antarctic ice, 

 even with the present moderate excentricity of the earth's 

 orbit, is unquestionable, and that its amount would increase 

 with increasing excentricity, is certain ; but I shall endeavour 

 to show in the next chapter, that it will always be very subor- 

 dinate to the influence of geographical conditions. 



Effect of currents in equalising the temperature of high and 

 low latitudes. — The dominant influence of the position of land 

 in reference to north polar temperature, is well shown by the 

 fact, that there is open sea nearer the pole than the northern 

 extremity of Greenland. That portion of the American con- 

 tinent, being of great height, is covered, between the 70th 

 and 80th degrees of latitude, with one uninterrupted mass 



melts 



boundary 



giving rise to icebergs in the neighbouring sea, by which 

 the cold is spread far beyond the limits of the snow-covered 

 land. Yet in spite of the chilling influence of Greenland, 

 there is open sea to the north of it, in a latitude where the 



oblinue and feebler. This is 



more 



marine 



warm 



the equalising effect of such currents, as regards temperature, 

 the Gulf-stream, already alluded to, affords the best illustra- 

 tion. It has its source in the Gulf of Mexico, which in 



R 2 





