274 



DEPTHS OF THE OCEAN 



Wind- 

 produced 

 currents. 



Boundary- 

 waves. 



sea. Supposing the coexistence of two different periodical 

 variations, one with a period of about twelve and a half hours, 

 the other with one of about fifteen hours, an infinite number of 

 variations would ensue, to which might be added the more 

 casual influence of the wind and other factors, causing among 

 other things incessant dislocations of the boundaries between the 

 different water-layers or currents. 



The wind may produce a current, particularly in the surface 

 layers, thus altering the direction and velocity of the existing 

 current. We know very little, however, about the relation 

 between wind and current, through lack of detailed observations, 

 although the question is naturally of the first importance from 

 an oceanographical point of view, as well as from its bearings on 

 the conditions of everyday life. This is one of the principal tasks 

 for the oceanographer of the future ; such observations are 

 diflicult to make, no 

 doubt, but with modern 

 methods much can be 

 done. 



A wind blowing over 

 the sea will carry the 

 surface water along with 

 it. In the open ocean 

 the current thus pro- 

 duced is generally somewhat deflected from the direction of the 

 wind itself. During the drift of the " Fram " over the North 

 Polar Sea, Nansen found that the ship, as a rule, was carried to 

 the right of the wind's course. V. W. Ekman has studied the 

 question theoretically, arriving at the conclusion that such a deflec- 

 tion is a result of the earth's rotation. Later, Forch, by extracting 

 the records from a number of ships' journals, found the same 

 deflection to the right in the Mediterranean and in the North 

 Atlantic, while, as might be expected, there is a deviation to 

 the left in the southern hemisphere. Now, as the surface-water 

 is carried along by the wind, the deeper layer will approach the 

 surface at the place of origin of the wind-current. In Fig. 184, 

 which represents one of Sandstrom's experiments, we see how 

 the wind may raise the boundary between the upper and lower 

 water-layers. When the wind ceases this rise again subsides, 

 producing a boundary-wave which will proceed farther. A wave 

 like this may attain a considerable height, without being 

 perceptible at the surface ; its dimensions will depend on the 

 distribution of density. A boundary-wave in the Norwegian 



Fig. 184.— Sandstrom's Experiment for producing 

 A Submarine Wave by a gust of wind. 



