no satisfactory exolanatlon can "be given of the fact that v/aves 

 frequently have a higher velocity than the wind which produces 

 them. 



Energy is dissipated by viscosity but the viscosity of the 

 water is so slight that this process can be neglected. There is 

 no evidence that energy is dissipated by turbulent notion in the 

 wave. The chief processes which can alter the wave height or 

 the wave velocity in deep water are therefore the push of the 

 wind, which becomes an air resistance if the wave travels faster 

 than the wind, and the drag or pull of the wind en the sea 

 surface. 



Knowing the rate of energy transfer from the wind and the 

 rate at which the wave energy advances (page 6) it is possible 

 to establish a differential equation from which the relationships 

 between the waves and wind velocity,- fetch, and duration are 

 obtained as special solutions. The equation contains three 

 numerical constants (including the "sheltering coefficient") 

 which have to be determined in such a manner that all the nine 

 empirical relationships are satisfied. This can be accomplished, 

 and at the same time discrepancies between existing empirical re- 

 lationships can be accounted for. 



The growth of waves as determined in this manner is illus- 

 trated in Figures 8 and 9 which are constructed on the assumption 

 that a wind of a constant velocity of 30 knots started to blow 

 over an undisturbed water surface extending for 600 or more nau- 

 tical miles from a coast line. Figure 8 shows the height and 

 period of the waves as functions of the distance from the coast 



21 



