The Tides 



77 



of these masses of matter causes the movable parts of its 

 surface, i.e., the water, to move. Not that the water really 

 makes any change of place excepting in its most superficial 

 parts, but it is, so to speak, swayed about in a manner which 

 makes its uppermost layers change their position. Thus the 

 tides, as observed at any given place, may be said to be 

 driven up by distant deep propulsion rather than drawn up 

 by influence directly from above. A clear perception of this 

 fact will simplify much, but there will still remain details for 

 the comprehension of which close attention will be required. 



It is customary to say that the southern hemisphere, and 

 especially the ocean between South America and New Zealand, 

 is the " Cradle of the Tides." By this expression is meant 

 that it is from this region that the great deep sea movements 

 may be said successively to start. From this point the swell 

 passes westwards and to the north. The course taken by 

 the swelling of the water is, as may readily be supposed, 

 modified locally by the formation of the land, but the force is 

 everywhere the same, and it is the continued attraction of 

 the moon, augmented in some seasons, hindered in others 

 by that of the sun. 



The ground swell which has started as suggested near New 

 Zealand, is under the same influences augmented in its course, 

 and finally after a prolonged interval is felt in the north 

 Atlantic, and reaches our British shores. The promontory of 

 Cornwall serves to divide the flow and to send one part north 

 by the Irish sea and west coast of Scotland to turn the Orkneys 

 and descend on the east. Another portion diverted eastwards 

 flows up the English channel, and the two may meet and 

 neutralise each other in the straits of Dover. Thus it will 

 easily be seen that the tide will rise up sooner on the south 

 coast of England than on the north and sooner on the west 

 than on the east. These are the main features, but there is 

 much yet to be explained. 



In some localities on our southern coasts where these 

 diverging streams again meet, great complications result in 



