314 



MAN AND THE GLACIAL PERIOD. 



outlet between Cuba and the peninsula of Florida. 

 Through this the warm water is forced into the region 

 where westerly winds prevail, and spreads its genial in- 

 fluence far to the northward, modifying the climate of 

 the British Isles, and even of far-off Norway. 



Pig. 100.— Map showing course of currents in the Atlantic Ocean: b and b' are 

 currents set in motion by opposite trade-winds ; meeting:, they produce the 

 equatorial current, which divides into c and c', continuing on as a and a 1 and e. 



But why are the southeast trade-winds of the Atlantic 

 stronger than the northeast? The ultimate reason, of 

 course, is to be found in the fact that the northern hemi- 

 sphere is warmer than the southern. The atmosphere 

 over the northern-central portion of the Atlantic region 

 is more thoroughly rarefied by the sun's heat than is that 

 over the region south of the equator. The strong south- 

 east trades are simply the rush of atmosphere from the 



