416 



General Theory of Ocean Currents in a Homogeneous Sea 



easy to test the properties required by the theory. Three consequences of the theory 

 are possibly most suitable for such a test: 



(1) the deflection of about 45° cum sole from the direction of the wind which is 

 almost independent of latitude (except near to the equator) ; 



(2) the restriction of penetration of the drift current by the frictional depth D; 



(3) the dependence of the sea surface velocity of the drift current on the shearing 

 stress of the wind. 



Angle of deflection. By special selection of oceanic areas, where it would be expected 

 that the wind alone would be decisive in determining the currents, Galle (1910) 

 showed that the deflection required by theory was actually present. For this he used 

 the large amount of data available for the Indian Ocean for all November months from 

 1858 to 1904 between 20° N. and 50° S. and 10° E. and 130° E. Taking together two 

 degree zones in each ten-degree field, the theoretical deflection to the right was obtained 

 in 77% of all cases in the Northern Hemisphere and in 69% in the Southern Hemi- 

 sphere. Three areas were examined with particular care: the sea between Socotra and 

 the Maldives, the South Equatorial Current and the west wind drift of higher southern 

 latitudes. Table 120 shows average values for larger areas. The mean of all values is 

 about 46° and in fact there seems to be no dependence on the latitude; both these 

 circumstances are in accordance with the theory for a constant frictional viscosity 

 coefficient. Forch (1909) used the survey on wind and current conditions in the Eastern 

 Mediterranean published by the "Deutsche Seewarte" to obtain an estimate of the 



Table 120. Mean angle of deflection in the Indian Ocean (cum sole) 



in all cases 



Table 121. Mean angle of deflection in the Eastern Mediterranean (cum sole) in all 



cases 



deflection of the current from the wind direction. The differences between wind and 

 current azimuth for the four larger areas are given in Table 121 as annual average 

 values derived from the monthly means. The mean of these rather scattered values is 

 around 42° cum sole. In the annual variation the angle is nearly 45° from December 

 to April, reaches a very high value in May and then during the warmer part of the 

 year from August to November is about 20°. It is possible that the strong surface 



