1910] McEwen: Preliminary Hydrographic Report. 199 



Avalon, Catalina, from La Jolla and south of Avalon to latitude 

 33°. the temperature is from 13.5° to 16.5°. The temperature 

 is about 18.5° from that point to latitude 32° 37', longitude 

 118° 41'. Thence southwest across the Cortez Banks the aver- 

 age temperature is 15.5°. The average temperature of the rest 

 nf the ocean is 19.0°. 



The breadth of this cold-water licit has not been determined 

 accurately, though observations show that it is confined to water 

 of one hundred fathoms or less in depth, and a drop of 2° or 3° 

 in two miles has several times been observed in a line normal to 

 the cold-water belt. 



All of these low temperatures occur where the depth is from 

 about twenty to one hundred fathoms, and are especially prev- 

 alent alone- the shallow belt of water parallel to the coast. 

 During the summers, when these observations were taken, the 

 winds were north or northwest and there was therefore a rela- 

 tively large component of the wind velocity parallel to the coast. 

 In October the winds shift to the west and the direction is then 

 mainly perpendicular to the const. 



The temperature phenomena can be accounted for. qualita- 

 tively at least, by means of a modern theory of oceanic circulation 

 due to V. W. Ekman. The most essential points of this extensive 

 theory, which apply to this case, are here briefly set forth. 



From the dynamical theory of the motion of the ocean water, 

 when the effect of fluid friction and the earth's rotation is 

 considered (it is understood that the wind is the only cause of 

 the current), the direction of the surface water current is about 

 45° to the right of the direction of the wind, instead of being 

 parallel to the wind, provided the depth of the water exceeds a 

 certain amount (the amount will be determined later), and the 

 region considered is north of the equator. The magnitude of 

 the velocity continually diminishes as the distance below the 

 surface increases, while the direction of the velocity continually 

 turns to the right. To be more specific, if Y„ is the surface 

 velocity and V the velocity at such a depth that the angle is a 

 with V , V = V e' a where (=2.718 (natural base for loga- 

 rithms), a = angle in radians; therefore when a = ir — 3.1416 

 radians or 180°. e _,r = .043 and l r =.043 V = approximately 



