OCEANOGRAPHY — ISELINT 261 



stations, it is evident that many of the early ideas are unsound. 

 Since it would be impracticable for any one institution to attempt 

 a complete survey of the North Atlantic, all existing observations 

 must be combined to show the general scheme of circulation and 

 test cases must be studied to explain the peculiarities. 



At the present time, among the foremost problems in ocean circula- 

 tion are the following: (1) The relative importance of wind and 

 convectional forces; (2) the question of whether ocean currents flow 

 steadily and in continuous paths or spasmodically; (3) the effect of 

 seasonal changes in surface temperature. As an initial approach to 

 the first problem there is a need for quantitative data. WTiat force 

 does a wind exert at the sea surface ? The question has been studied 

 by the mathematician, Ekman, and the theory of his famous spiral 

 is well known. It has been suggested that if the wind drives the 

 surface layers of the ocean they in turn must retard the lower strata 

 of air. Ekman's spiral should exist in both the ocean current set-up 

 and in a reversed direction in the lower layers of the atmosphere. 

 Since it is more easily measured from the meteorological point of 

 view through pilot-balloon observations than in the ocean, it may be 

 possible for students of aerodynamics to secure for oceanographers 

 actual values of the force exerted at the sea surface by the wind. 



The second problem, concerning the steadiness of ocean currents, 

 is perhaps too technical to discuss here since it involves the usefulness 

 of Bjerlmes's equations. His theory for calculating the velocity of 

 currents by the slope of the surfaces of equal density demands that 

 the circulation has assumed a steady character. There is some rea- 

 son to believe that ocean currents are usually either slowing up or 

 increasing their velocity and often break down altogether. The im- 

 mediate question before physical oceanographers is how far it is 

 advisable to use for dynamic calculations stations from different ex- 

 peditions or even from the same expedition, but made over a period 

 of a month or more. It may be that in certain regions the ocean 

 circulation is disturbed by eddies corresponding to the extra-tropical 

 cyclones of meteorology, in which case nothing but simultaneous sta- 

 tions will give a true picture of the circulation. In the case of the 

 northern areas of the Atlantic, the third problem is immediately 

 brought up. Are the seasonal temperature changes in the surface 

 layers powerful enough to alter the underlying dynamic forces? 



There are many more perplexing questions having to do with 

 circulation which are still unsettled, but the above is perhaps suffi- 

 cient to show that the understanding of oceanic circulation is still 

 in a very elementary stage in spite of what one might think from 

 examining the very considerable literature on the subject, unfor- 

 tunately mainly based on insufficient data. In other words, the 



