DISCOVERY OF THE TWO CURRENTS. 319 



with the earth, and again rises to form the 

 upper current, being displaced by the cold and 

 heavy, air flowing from the poles. There is 

 thus a sort of atmospheric chain formed, which 



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will be more clearly understood by reference 

 to the cut. At all places, however, above the 

 latitude of 30, in consequence of the variations 

 in the amount of heat received from the earth, 

 these currents are very irregular. 



Now, this upper current, having a different 

 velocity, in consequence of its origin at the 

 swiftly rotating equator, to that of the more 

 northerly or southerly slower moving regions 

 which it has now reached, takes on the apparent 

 character of a wind from west to east, and thus 

 appears as a westerly wind. And when the 



