AND OTHER WATER WAVES 169 



Thus in an ordinary cyclonic storm, advancing from 

 the Atlantic, the principal waves, rounding Old 

 Harry Rocks to the westward, come in directly 

 upon the shore with a south-westerly wind more 

 or less behind them. In the clearingi weather which 

 generally follows, with north-westerly wind, the 

 waves generated at a distance continue to advance 

 upon the shore, but the wind is now against them, 

 and spray is often torn from the crest of the breaker 

 and driven seawards. Under these different condi- 

 tions the position of the breakers is quite different. 

 In the first case i.e., with strong on-shore wind 

 there is more than one line of breakers, but even 

 the final line is situated far from the shore, and 

 between it and the beach there is a somewhat 

 numerous series of bores, or roll waves. 



When, on the other hand, the wind is off-shore, 

 with a rough sea in the offing, waves do not break 

 until they come quite close to the beach. The 

 breakers, moreover, curl over in a well -formed cusp 

 and occasion a loud report. This noise is ap- 

 parently due to the escape of the air which has 

 been momentarily imprisoned when the cusp has 

 curled over upon the front of the wave. Although 

 they come so close to the shore before breaking, 

 their height, reckoned above the antecedent trough, 

 is sometimes as great as that of the breaking waves 



