ON THE EFFECTS OF OCEANIC CURRENTS UPON CLIMATES. 



455 



If we bring together tbe January effects of the Gulf Stream in the 

 North Atlantic, and of the Kuro-Sivvo in the North Pacific, we shall see 

 the difference between them most clearly. 



Effects of Gulf Stream (oul Kuro-Siii-o iqwii January 'J'emj!c'ratu7'cg. 



The following considerations help to explain the differences produced 

 in the North Atlantic and North Pacific by their respective systems of 

 ocean-circulation : — 



1. The ocean-currents at the equator and within the tropics are caused 

 by the trade winds. 



2. The trade winds are caused by the equatorial evaporation and sub- 

 sequent precipitation of vapour as rain, and the force of the trade winds 

 is proportional to the rate of evaporation. 



Combining these propositions, we find that the volume of the equa- 

 torial current will be proportional to the equatorial breadth of the ocean 

 and to the rate of evaporation, jointly. 



The following tables show the mean annual temperatures of the tropical 

 latitudes of the North Atlantic and Pacific Oceans. 



Latitude 



0° N. 

 10° N. 

 20° N. 



Mean 



77-48° F. 



The ratio of tlie mean breadths of the two oceans in the given lati- 

 tudes is — 



Pacific ^ 1600 _ 



Atlantic 625 



2-56 



The ratio of the vapour-tensions of the mean annual temperatures of 

 the two oceans, in the given latitudes, is — ■ 



Pacific _ Vapour Tension of 77°-48 F . _ 0-947 in. 

 Atlantic ~ Vapour Tension of 79°-38T. ~ l-QOl in. 



Hence, the approximate ratio of the volumes of the Pacific and Atlantic 

 equatorial currents, which produce the Kuro-Siwo and Gulf Stream, is 



1600 947 ^ 

 625 1001 



