THEORIES OF OCEAN CURRENTS 



141 



possible factors as influencing ocean currents. The m;iin 

 causes are divisible into two groups (i) Those within the 

 water c>g., differences in density, temperature, and salinity, 

 which are in part due to geographical causes, such as varia- 

 tions in sunlight, evaporation, rain-fall, or melting ice; and 

 (2) those outside the water e.g., wind and its causes, i.e., 

 variation in atmospheric pressure. 



Among the secondary influences is friction, which doubt- 

 less plays a part in all movements of sea-water ; the rotation of 

 the earth, and the geographical configuration of the coast-line. 



OOO 



FIG. 27. DEVIATION OF OCEAN CURRENTS DUE TO EARTH'S 

 ROTATION. (KRUMMEL.) 



THE INFLUENCE OF THE EARTH'S ROTATION. 



All surface currents, whether of air or water, are affected 

 by the earth's rotation, and in such a manner that in the 

 Northern Hemisphere they are deflected to the right and in 

 the Southern Hemisphere to the left. The deflection varies 

 with the latitude, and is at its maximum at the Poles, and at 

 the Equator non-existent. 



The influence of the rotation of the earth on ocean currents 

 has been determined by direct observation. Since the waters 

 of the sea and ocean are influenced by tidal streams, winds, 



