68 THE OCEAN 



causes the great rollers and breakers which 

 we see upon our coasts after heavy storms. 

 The larger the waves the greater the depth of 

 water affected by them and, when this depth 

 is sufficient, the lower portions of the waves 

 are held back by the bottom of the sea near 

 the shore and the upper parts travel more 

 rapidly and break or curl over the lower por- 

 tions. This breaking of waves upon a shore 

 gives a still greater appearance of the water 

 itself travelling forward, but between the 

 waves the water flows back to its normal 

 height, which would not be the case if the 

 water itself were really moving forward, as in 

 the case of the tide. 



Out at sea, in deep water, even the very 

 largest waves do not break and curl, save 

 where they come into contact with some other 

 object or other waves or when their tops are 

 blown off by the wind. When the wind trav- 

 els faster than the waves the tops are forced 

 ahead of the lower portions and the waves 

 break in much the same manner as when the 

 lower parts drag on the shore, for in each 

 case the upper parts of the waves travel faster 



