Equation (42) can be Interpreted either to mean that half the 

 energy (E/2) Is propagated with the phase velocity, or that the rate 

 of transmission of total energy E is equal to the group velocity 

 c = (r/2. 



From (41) 



^tf *Etf = (A-^>^ (^^^ 



or 



A(|f *c^) *E (^*cfi-) = (A-D)X . (45) 



Let us consider two cases: 

 Case A ; If a constant wind with mean velocity v blows over an un- 

 limited sea room (fetch), and if the energy added is the same every- 

 where so that the waves grow at all localities at the same rate with 

 time t (duration), then 



and equation (45) reduces to 



^^ 



I- If = A - D. (46) 



With (43) and the substitution (33) we have 



Pga ^ . £f! If. = , . :>. (47) 



Case B ; If, on the other hand, the duration, t, of wind action is 

 unlimited or in practice long enough to produce a steady state, but 

 the fetch x is limited, then for local steady state conditions 



dE _ 

 In this case, 



= 0i |i- = 0. 



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