

Cu. XX.] 



GREATEST VELOCITY OF CURRENTS 



501 



motion, relatively to the land and water with which it would 

 come into juxtaposition, would be such as to cause an appa- 

 rent motion of the most rapid kind (of no less than 200 miles 



an hour) from east to west. 



In the case of such a sudden transfer, the eastern coast of 



mi 



tremendous 



and a considerable part of the continent might be sub- 

 merged. The disturbance does not occur, because the water 

 of the stream, as it advances gradually into new zones of the 

 sea which are moving more rapidly, acquires by friction an 

 accelerated velocity. Yet as this motion is not imparted 

 instantaneously, the fluid is unable to keep up with the 

 full speed of the new surface over which it is successively 

 brought. Hence, to borrow the language of Herschel, when 

 he speaks of the trade winds, ' it lags or hangs back, in a 

 direction opposite to the earth's rotation, that is, from east 

 to west;'* and thus a current, which would have run simply 

 towards the north but for the rotation, may acquire a relative 



direction towards the west. 



We may next consider a case where the circumstances are 



the converse of the above. The Gulf 



stream 



i=> 



lm 



miles 



miles, or 174 miles 



slower. 



motion 



may 



velocity, tending continually to deflect it eastward. Polar 



from 



tudes, are driven towards the eastern shores of continents, 

 while tropical currents flowing towards the poles are directed 



against their western shores. 



Thus it will be seen that currents depend, like the tides, 



circumstances 



motions 



But 



sum 



may 



yet the points where these operations are displayed in fullest 



* Treatise on Astronomy, chap. iii. 



