



■ 



ftf 



k 



.' 



It. 



but 

 ■ 



ion 



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r 







and i 











he 



't 



jng- 



from 





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ti 



[?*< 



** 



Ch. XX.] 



CURRENTS. 



4 5 



Nova 



Scotia, rise to the height of seventy feet. 



some 



offer an exception to the rule above mentioned ; for while 

 here is scarcely any rise in the estuary of the Plata in South 



I 



America, there is an extremely high tide on the open coast 

 of Patagonia, farther to the south. 



Yet 



the tides reach their greatest elevation (about fifty feet) in the 



Magellan, and so far at least they conform to the 



general rule. 



>/ 



movements 



magnitude should be impressed on a wide expanse of ocean, 

 by winds blowing for many months in one direction, may 

 easily be conceived, when we observe the effects produced in 

 our own seas by the temporary action of the same cause. It 

 is well known that a strong south-west or north-west wind 

 invariably raises the tides to an unusual height along the 

 west coast of England and in the Channel ; and that a north- 

 west wind of any continuance causes the Baltic to rise two 

 feet and upwards above its ordinary level. Smeaton ascer- 

 tained by experiment, that in a canal four miles in length, 

 the water was kept up four inches higher at one end than at 

 the other merely by the action of the wind along the canal ; 

 and the late Major Eennell informs us that a large piece of 

 water, ten miles broad, and generally only three feet deep, 

 has, by a strong wind, had its waters driven to one side, and 

 sustained so as to become six feet deep, while the windward 

 side was laid dry.** 



As water, therefore, he observes, when pent up so that it 

 cannot escape, acquires a higher level, so, in a place where it 

 can escape, the same operation produces a current ; and this 

 current will extend to a greater or less distance, according to 

 the force by which it is produced. 



divided currents 



according to their 



The same writerf has 

 origin into drift- and 



stream-currents ; the former being due to constant and preva- 



nt winds impelling the sum 

 eets with some obstacle whi 



* Eennell on the Channel Current. 



t Investigation of the Currents of 1832. 



until it 



the Atlantic Ocean, page 21. London, 



