148 A TEXTBOOK OF OCEANOGRAPHY 



to be 22- 1), B r the original similar atmospheric pressure in 

 the North and Baltic Seas, and B the new pressure over the 

 North Sea. 



Knudsen thinks that the influence of the atmospheric 

 pressure on the currents in the Belt is much more marked 

 than 4he wind. 



WIND AND OCEAN CURRENTS. 



The influence of the wind has long been disputed as a 

 cause of ocean currents, though navigators have always 

 inclined to the theory that wind is an important factor. 

 Franklin thought the trade winds were the cause of the 

 tropical westerly current met with where they prevail, and, 

 indeed, he thought that the wind was the principal cause of 

 ocean currents. Rennell divided ocean currents into two 

 groups drift currents, directly attributable to prevailing 

 wind ; and stream currents, due to the stemming or damming 

 of drift currents by the coast or other currents. Stream 

 currents can flow against the prevailing winds. Most British 

 geographers adopt Rennell's classification. Findlay says, 

 however, that the wind can only influence quite superficial 

 layers of water, at the most to a depth of 5 or 6 fathoms. 



OCEAN CURRENTS. 

 The Atlantic Ocean. 



The currents of the Atlantic Ocean have been observed in 

 more detail than either of the other oceans. 



It is convenient to consider the Atlantic currents under five 

 headings viz. : 

 . i. The equatorial currents. 



2. The Florida Current (the so-called Gulf Stream). 



3. The South Atlantic currents. 



4. .Deep-sea currents. 



