37 



northern boundaries of the general North Atlantic drift, and of its 

 extension toward the Norwegian Sea. Diiring the svurjuer of 1923, 

 the U. S. Coast Guard carried out a general d^oiai^ic survey of the 

 circulation of the region of Davis Strait. And we similarly expect 

 from the nujnerous observations taken by the "Meteor," in the 

 Equatorial and South Atlantic, a general circulatory picture for 

 that ocean, for conparison with the scheme deducible from the dis- 

 tribution of temperature and of salinity, and from the drifts re- 

 ported in ship's logbooks. 



From the standpoint of ocean geophysics as a whole, however, 

 the greatest service to be expected from such developments in 

 quantitative analysis is that here, at last, we have a means of 

 numerically testing the actual efficiency, as a motive power of 

 ocean currents, of one of the two great forces that have usually 

 been invoiced as the underlying causes for the existence of a con- 

 tinuing non-tidal circulation in the sea. We refer to the regional 

 inequalities in the specific gravity of the ocean waters that are 

 maintained by heating at low latitudes, chilling at high, combined 

 with the regional differences in salinity that result from rivor- 

 inflow, from evaporation, and fron rainfall. 



In this field, the task imm.ediately urgent is to determine, for 

 as many sectors of different currents as possible, and for as nany 

 different ocean areas, whether the internal hydrostatic forces at 

 work are, or are not, quantitatively sufficient, and do, in fact, act 

 in the diroction proper to produce the general type and velocity of 

 circulation that other lines of evidence have shown to prevail, Hore 

 specificall:,^, examinations of particular sectors of the so-called 

 "Gulf Stream," of the Labrador current, of the East Greenland, the 

 Benguela, the Alguhlas, or the Japan currents (among others) iwrj be 

 expected to show how far such highly developed, and definitely 

 localized drifts receive their impetus from internal archimedian 

 forces acting along their courses, or how far some other force (i.e., 

 the winds) must be invoked to explain their persistence. The 

 dynamic studies carried on in the Northwestern Atlantic since 1925 

 have had this as one of their im^nediate objects, and their fertility 

 justifies the extension of explorations with this definite aim. 



Before the frictional effects of the winds relative to that of 

 internal hydro-statics can be finally established as a major motive 

 force (scientific opinion has long swung firat to the one then to 

 the other), wind currents must also be analyzed more searchingly 

 and on a much larger scale than has yet been possible. The 

 mechanical principle in question here is simply the downward pro- 

 pagation, into the water, by friction, of motion given to the sur- 

 face filiT: by the direct frictional drag of the wind. But it awaited 

 Ekman's mathematical genius to prove that the earlier concepts of 

 wind currents were erroneous because, they did not correctly allow 

 for the doflective force of the earth's rotation, and to explain 

 the peculiar spiralling of such currents v.'ith increasing depthr;. And 

 the fact that the wind-drift actually recorded has usually failed to 

 coincide, by many degrees of azimuth with the theoretic requirements 

 shows that more critical quantitative treatment is still needed to 

 establish some numerical expression for the effects of vertical 

 density gradients and of the contour of the bottom (which have to 



