34 



Taere is, as yet, no general agreement of scientific opinion 

 as to the causes of these variations, for all that has yet been 

 possible, in any individual case, has been to show an apparent 

 correlation between the event, and some outstanding solar or other 

 cosriic hapoening. Some students have regarded such fluctuations 

 as due, in the last analysis, to variations in the amount of energy 

 (i.e., heat) that reaches the earth from the sun. But others main- 

 tain that these solar variations are insufficient to account for 

 phenomena known to take place. And even if the solar control 

 theory be accepted, the intervening mechanism by which solar varia- 

 tions might be translated into the variable pulses and curious 

 dislocations shown by the ocean currents is still to be worked out. 

 Does this take place via the medium of changes in the prevailing 

 strength and direction of the winds, caused by shifts in the loca- 

 tions of the centers of high and low atmospheric pressure? Does 

 more or less active heating of the waters around the Tropic belt 

 send greater or lesser volumes of warm water poleward, or is the 

 Antarctic shelf the cradle of all the world-wide disturbances in the 

 current systGi^:B of the oceans, as at least one emminent oceanographer 

 would have us believe? 



Or must we conclude, as do some students, that the solar varia- 

 tions are too small, and the ability of the sea to absorb and 

 smooth out their effects too great (owing to the great capacity of 

 water for heat), for fluctuating currents to be explained in this 

 way? In that case the theory that periodic changes in gravitation 

 are responsible, caused by the regular secular changes in the rela- 

 tive positions of earth, moon, and sun, must be critically weighed. 



The possibility that events taking place around the sub- 

 antarctic belt, where vast masses of ice break off, may exert far- 

 reaching effects, translated in the end into climatic variations in 

 distant parts of the earth, brings to our attention another problem 

 with which physical oceanographers have long been much concerned; 

 namely the relative importance that melting ice plays in the complex 

 of factors that keep the oceanic circulation in motion. Here the 

 present need is not so much for rehashing the old arguments, pro 

 and con , as for much more extensive investigation actually around 

 the ice edge than has yet been possible. At first sight this might 

 seem an especially favorable subject for experiment under labora- 

 tory co7itrol, for one can easily put a piece of ice in water and 

 observe what takes place as the ice melts. But one of the reasons 

 why the relative efficacy of melting ice as a causative agent for 

 ocean currents is still a matter for dispute, is uncertainty as to 

 whether the results seen in laboratory tanks, or in some small 

 fjord, do actually simulate the conditions that prevail over the 

 broad eiq^anses of the open ocean, closely enough (quantitatively 

 as well as qualitatively) to be accepted as representative of what 

 actually happens in nature. 



The regional and descriptive phases of oceanic circulation 

 lead naturally to a presentation of the present state of knowledge 

 as to the interplay of forces that maintain this circulation. New 

 viewpoints in this field have follov;ed the recent development of 

 quantitative methods of estimating the relative efficiency of the two 

 major forces rost obviously concerned; namely, the internal hydro- 

 statics of the water itself on the one hand, and the frictional 



