according to L. Prandtl [20] 



l^o' 2 



(.- ^J 



where z depends on the roughness of the surface over which the 

 air is flowing, and is called the roughness parameter, ot the "rough- 

 ness length." The nondimensional quantity k is approximately con- 

 stant and has the value 0.40. z is the "anemometer height" where 

 the wind velocity v is measured. The dimensionless factor 



k /[ln(z + z )/z )] corresponds to the frictional factor or effect- 



,V[ln(z + Zo^/^o^^^ 

 ive resistance coefficient in (24). 



If we consider the effective resistance coefficient for p>l/3 

 to he given by (25) as a function of the stage of wave development 

 or the wave age p, it follows with (17) from equation (12) that 



A = p'v^p[Y^(p) + s'TT n e'^^^d - p)^] , l/3<P^l , (2?) 



is the rate at which work is being done by the wind on a wave, which 

 is characterized by its wave age p. 

 With 



CgCP) = Y^(P) + s'TT n e"^^(l - p)^ ; l/3^p<l , (28) 

 equation (27) can be written 



A = p'v^pC2(p) . (27a) 



When the waves proceed in development and longer waves are gene- 

 rated with p*>l 



A = p'v3p*C^(p) ; l:$p*<Pj^* , (29) 



where 



66 



