246 



G. F. Me E wen. 



Conversely, if a large body of water be shown to have a nearly 

 uniform summer temperature, corresponding in general with the normal 

 value for the latitude, and with local circumstances in its particular 

 portions, this is, of itself, evidence that no large body of water intrudes 

 within its borders from a region of a different normal temperature. In 

 other words, in the general oceanic circulation, a stream of water with 

 a temperature normal to one latitude can not move to a region where 

 another temperature is normal without exhibiting its presence by a de- 

 flection of isothermal curves. 



4 



ft 



200 400 600 800 ICOO 1200 1400 1600 1800 2000 



100 300 500 700 900 1100 1300 1500 1700 1900 



Depth in Meters 



Fig. 3. 



The source of the energy required to set and keep in motion the 

 vast mass of ocean w^ater has been productive of endless discussion. 

 The attractive force of the moon, the lag of the water itself, the 

 difference in temperature and density of the equatorial and polar regions, 

 the unequal distribution of the atmospheric pressure has each in its 

 turn been proposed and strenuously advocated as the true and only cause 

 of ocean currents. To the seaman, however, the cause of the ocean 

 currents has always been the winds, the motion of the waters of the 

 sea taking its origin in the region where the winds attain their maximum 

 constancy, that is, in the region of the trade-winds. 



The following results of Zoppritz's (2) theory of ocean currents 

 have been widely used by hydrographers. A perfectly steady wind 

 acting continuously on the surface of the sea will thru friction, give 

 rise to a movement of the surface waters in the same direction as the 

 wind, itself. If the latter continues for a sufficient length of time, the 



