PHYSICAL OCEANOGRAPHY 263 



ledge of the motions of the sea, for which purpose direct 

 current-measurements are necessary. 



Measuring the currents at different depths in the sea is 

 much more difficult than might appear at first sight, and re- 



Ekman's Current-Meter. 



quires good apparatus. Many excellent current-meters have 

 been constructed, the one made use of during the cruises of 

 the " Michael Sars " being that invented by V. W. Ekman, Ekman's 

 represented in Fig. 177. The apparatus consists ot a double 

 wing (A), that points in the direction of the current. In front 



current- meter. 



