134 THE OCEAN RIVER 



the cooling and warming of the water in the north and south, 

 is the main cause of their more rapid or slower deviation and 

 progress toward the east or west ... we ought to apply to the 

 ocean the same theory which has already afforded a satisfac- 

 tory explanation to the trade winds if we will decipher the 

 question of currents." 



Maury added his opposition to the wind theory on the 

 grounds that a current caused by winds would cease as soon as 

 the wind dropped, so that permanent continuous currents 

 would be impossible. In opposition to Arago he firmly be- 

 lieved that the different density of sea water in different parts 

 of the ocean, caused partly by unequal heating, is sufficient to 

 account for currents. Perhaps the most striking of Maury's 

 ideas was that the center of the Stream rises to a higher level 

 than the sides. If this were so a surface flow of water would 

 continually run off toward the edges, which is an obvious 

 impossibility. 



As the nineteenth century drew toward its end the contro- 

 versy continued, some arguing for wind causes and some for 

 density causes. Even the scientists of the Challenger expedi- 

 tion were divided — Wyville Thompson and W. B. Carpenter 

 held firmly opposed views on the problem. One opponent of 

 the wind-current theory, Zoeppritz, proved to his own satisfac- 

 tion that wind forces would require hundreds of thousands of 

 years to whip the ocean into continuous deep currents. He was 

 not entirely without reason. If water flowed with perfect regu- 

 larity and smoothness the wind would disturb only the imme- 

 diate surface, and this purely superficial motion would with 

 difficulty be imparted to the layers below. But five years later 

 Osborne Reynolds used dyes to cause colored streaks in water, 

 and with this simple device made the apparently unrelated 

 discovery that water in pipes flows as a series of distinct layers 

 and not as a smooth undivided whole. As one layer of water 

 moves over the other an irregular eddy action takes place 



