THE OCEAN 181 



The surface currents of the ocean have a 

 different origin, for they depend upon winds, 

 especially trade winds, etc. Such continuous 

 action of moving air upon water has been 

 theoretically explained by Helmholtz and 

 Zopperitz. Needless to say, in addition to 

 these principal causes there are a great variety 

 of lesser factors which assist in the formation 

 and preservation of ocean currents. 



It is impossible here to undertake an analy- 

 sis of the phenomenon, but certain it is that 

 into the processes that constantly stir the 

 ocean, beside the rotation of the earth, the 

 eccentricity of its orbit, and the inclination of 

 its axis, the thermal properties of water enter 

 as fundamentally important factors. 



The magnitude and the extent of the 

 movements which result from such influences 

 are very considerable. The principal surface 

 currents are oval in form, one in the North 

 Pacific between 10° and 50° north latitude, 

 one in the North Atlantic between 10° and 

 30° north latitude, one in the South Pacific 

 between 5° and 45° south latitude, one in the 

 South Atlantic between 0° and 40° south 

 latitude, and one in the Indian Ocean between 

 0° and 40° south latitude. The greatest of 

 these are the Pacific currents. In the far 

 south is an Antarctic current flowing from 



