9.P 



8 



in certa.in enclosed seas (Mediterranean and Red Sea), as well as in 

 the Trade Wind belts; the up-wellings from the abyss; the regions 

 where water, chilled to a high specific gravity, pours downward from 

 the surface; the regions of active turbulence, where the surface is 

 chilled, the bottom warmed, etc. The evidence of salinity is 

 especially instructive with respect to deep currents, because this 

 feature of a body of water below the surface is altered only if it be 

 forcibly intermingled with water of some other character, _ whereas 

 cold v/ater may be warmed, or warm water cooled, by radiation, with- 

 out any such mixing. And while the knowledge of currents to be ob- 

 tained from temperature and salinity (each v/eighed per se ) is 

 strictly qualitative, up to date it has given us almost our sole 

 reliable clue to the movements of the waters of the deeps. 



Even with the modern development of quantitative methods of 

 studying ocean currents, the simpler lines of qualitative evidence 

 must not be neglected, because the two illuminate different aspects 

 of the circulatory problem. The former throw light on the direction 

 and velocity of flow prevailing at the time of observation, and to 

 be expected as long thereafter as conditions continue stable, But 

 when we find, let us say, a tongue of cold water extending down along 

 the Grand 3anlcs from the north, with bergs floating in it, we see the 

 result of events that have been taking place for some time previous: 

 i.e., we glimpse oceanographic history. And by plotting these _ 

 simple physical features of the ;^'ater periodically, it is possible to 

 follow the relative contractions and expansions of different water- 

 masses as long as these continue. Thus in Physical Oceanography, as 

 in every one of the geo-physical sciences, the qualitative-des- 

 criptive method of study must proceed hand in hand with the quanti- 

 tative, if we are to gain a just picture of events as they actually 

 occur in nature. 



In this case, as is usually true of broad-scale phenomena, the 

 dependability of the results rests largely on the number of observa- 

 tions taken, • And as we have to do with dynamic phenomena, rather 

 than with static, the more nearly simultaneous the observations can 

 be made the better. 



NatU-L-ally, these technical requirements have best been met in 

 the more frequented and more fished parts of the North Atlantic and 

 of its tributary seas. Qualitative studies of the currents at 

 different depths have, in fact, been prosecuted so intensively in 

 limited areas in the North Sea, the Norwegian Sea, the Bay of Biscay, 

 the Straits of Gibralter, the Gulf of St. Lawrence, the Gulf of Ifeine, 

 around the Grand Banks, and in the Straits of Florida, that the pre- 

 vailing systems of motion have been v/orked out there, surface to 

 bottom. This applies also along the coasts of southern California, 

 likewise around Japan; but nowhere else as yet. 



When we turn to the ocean basins, outside the margins of the 

 continents, there is crying need for the raw data (temperature and 

 salinity) for current plotting (Page ;:5 ), Lacking this t;o still 

 fail to comprehend more than the most general aspects of the drifts 

 over the floors of the abyss - movements that are as important a 

 part of the picture from every point of view (except the navigational) 

 as is the circulation of the surface. And our ideas as to the 



