14 PHYSICAL GEOGRAPHY OJ? THE SEA. 



altered mean temperature of those ocean plains tban in the 

 changed medium warmth of the dry land." 



The warmest part of the ocean does not coincide with the 

 Equator, but seems to form two not quite parallel bands to the 

 north and south. 



In the northern Atlantic, the line of greatest temperature (87° 

 F.) which on the African coast is found but a little to the north ol 

 the Equator, rises on the north coast of South America as high 

 as 12° N. lat., and in the Gulf of Mexico ranges even beyond the 

 tropic. The influence of the warmth-radiating land on inclosed 

 waters is still more remarkable in the Mediterranean (between 

 30° and 44° N. lat.) where during the summer months a temper- 

 ature of 84° and 85° is found, three degrees higher than the 

 medium warmth of the open tropical seas. 



While in the torrid zone the temperature of the ocean is 

 generally inferior to that of the atmosphere, the contrary takes 

 place in the Polar seas. Near Spitzbergen, even under 80° N. 

 lat., Graimard never found the temperature of the water below 

 + 33°. Between Norway and Spitzbergen the mean warmth of 

 the water in summer was +39°, while that of the air only 

 attained +37°. 



In the enclosed seas of the Arctic Ocean, the enormous accu- 

 mulation of ice, which the warmth of a short summer is unable 

 totally to dissolve, naturally produces a very low temperature of 

 the waters. Thus, in Baffin's Bay, Sir John Boss found during 

 the summer months only thirty-one days on which the tempe- 

 rature of the water rose above freezing point. 



In the depths of the sea, even in the tropical zone, the water 

 is found of a frigid temperature, and this circumstance first led 

 to the knowledge of the submarine polar ocean currents ; " for 

 without these, the deep sea temperature in the tropics could 

 never have been lower than the maximum of cold, which the 

 heat-radiating particles attain at the surface." * 



It was formerly believed that while the surface temperature — 

 which depended upon direct solar radiation, the direction of 



currents, the temperature of winds, and other temporary causes 



might vary to any amount, at a certain depth the temperature 



was permanent at 4° C, the temperature of the greatest density 



of fresh water. Late investigations, however, have led to the 



* Humboldt's " Kosmos." 



