regularities in the relation between wind and sea state at differ- 

 ent wind speeds, which do not stand out if only single observations 

 under different conditions are taken at random, or when the observed 

 periods are averaged over the whole range of scattering values. 

 This perhaps explains the fact that the older attempts to determine 

 empirical relationships between wave periods or wave lengths and 

 wind velocity led to less satisfactory results. 



The most conspicuous feature of the sea surface pattern at all 

 wind velocities is, as already mentioned, the occurrence of the 

 steepest characteristic waves, which are slower than the wind velo- 

 city. They are indicated in Fig, 1-3, 4 and 5 hy the period T^» 

 The curve T, in Fig. 5 is based on previous calculations of the re- 

 lationship between the dimensions of fully developed wind waves and 

 the wind velocity in the composite wave motion (G. Neumann [8]), The 

 condition that the energy supply by wind to waves equals the energy 

 dissipation by turbulence at f\illy developed sea leads to a theo- 

 retical relation 



2. 2r(-^ - 1) 

 T,(sec) = f^ 2 V (la) 



^ ^ In 182.5 - J In V 



where v is the wind velocity in cm/sec, <r2 the propagation velocity 

 of the fully developed "longer waves" in cm/sec (see [8]]^ g the ac- 

 celeration of gravity, and the dimensionless constant r = I.667. 



In denotes the natural logarithm. With the value (T'o/v = ft *= 1,37 



^ "^m 



formula (la) leads to the same periods as evaluated formerly [8], 

 except at wind velocities lower than 3-4 m/sec, where the periods 

 given by (la) are slightly larger than the periods given in the paper 



19 



