CHAPTER III 



The wave-length of the swell which reaches the shore after 

 storms The height of the swell at sea during storms 

 The co-existence of waves of different lengths The 

 give and take between air and water in the develop- 

 ment of waves. 



The Wave-length of the Swell which reaches the 

 Shore after Storms 



WHEN the waves produced upon the deep sea run 

 into water of which the depth is less than i-4th 

 the wave-length, theory shows that their speed is 

 reduced 6.7 per cent., and when the depth is no 

 more than i-8th of the wave-length their speed 

 is only 4-ioths of what it was in deep water. 1 

 This reduction of speed goes on as the wave 

 approaches the shelving shore. Finally, in water 

 of which the depth is only a small fraction of the 

 original wave-length, the wave -speed is the same 

 in all cases, no matter what was the original speed 

 and wave-length in deep water. This progressive 



1 Vide Sir G. G. Stokes' " Admiralty Manual," 1886. 



85 



