500 



GEEATEST VELOCITY OE CUEEENTS. 



[Ch. XX 



per hour ; but when the boundary lands converge, large 

 bodies of water are driven gradually into a narrow space, 



room 



level Whenever this occurs, their velocity is much increased. 

 The current which runs through the Kace of Alderney, 



name 



main land, has a velocity of about eight miles 



Hewett 



miles 



o 



storms. The greatest 

 vek>cit7oV the tidal current through the < Shoots' or New 

 Passa-e in the Bristol Channel, is fourteen English miles an 

 hour ; & and Captain King observed, in his survey of the 



the tide ran at the same rate 



geographical 



Straits 



Ma 



Narrows 



through the ' First 



miles an hour in other parts of those straits. 



Each of the live causes above mentioned— the wind, the 

 tides, evaporation, the influx of rivers, and the expansion 

 and contraction of water by heat and cold— may be conceived 

 to operate independently of the others, and although the in- 

 fluence of all the rest were annihilated. But there is another 

 cause, the rotation of the earth on its axis, which can only 



when the waters have already been set in 



one or all of the forces above enumerated, 



and when the direction of the current so raised happens to 



come 



motion bv some 



from south to north, or from 



The principle on which this cause operates is probably 

 familiar to the reader, as it has long been recognised in the 

 case of the trade winds. Without enlarging, therefore, on 

 the theory, it will be sufficient to offer an example of the 

 mode of action alluded to. When a current flows from the 



Hop 



mass 



miles 



turns 



at a parallel where the surface of the earth is whirled roun 

 at the rate of 1,000 miles an hour, or about 200 miles faster. 

 If this great mass of water was transferred suddenly Ironi 

 the higher to the lower latitude, the deficiency of its rotatory 



