W^ a J p'c^Cv - a-)2.A ,Cg sec"^] (26a) 



for the siirface area of the width one and the length X , c^ may 

 be evaluated by the values of p determined by experiments. The 

 results of Motzf eld's measurements seem to indicate the proportion- 

 ality c^~ivd)-^^ , but it seems uncertain whether these results of 

 measurements over smooth, rigid wave profiles are applicable to 

 the conditions at the actual sea surface. 



Using an empirical relationship [13 ] between the wind force 

 exerted at the rough sea surface and the wind velocity, "^^ff - f(v), 

 the author [8], [13] made an attempt to estimate the effective 

 value of the wind force as a ftmctlon of wave development at differ- 

 ent wind velocities. By means of a relationship between 6 and p, 

 as suggested by Sverdrup-Munk [1], it was possible to relate 

 ■J* X. - = F(p(v)) where, according to a previous paper [14] 



Cj = sa^ = sir6 , (l6) 



with s = 0.095 was used as suggested by empirical evidence. Both 

 assumptions (15) and (16) lead to nearly the same numerical values 



Cj,, when considering initial waves with the steepness 6 - l/lO. 



— 2 2 ••2 



This follows with Jeffreys* assumption from (15) sv 8 = 2.96 • 10 , 



and from (16) sir5 = 2.98*10 . But when considering the generation 

 and the growth of initial waves with increasing wind speed 11; seems 

 that the relation (16) holds good. The determination of the c^j-value 

 at different conditions of the sea surface is necessary for an exact 

 evaluation of energy transfer from wind to waves, and fiorther in- 

 vestigation of this point is Indicated. 



Another important empirical relationship deduced from experience, 



59 



