characteristic waves has more long stretched wave crests, as al- 

 ready pointed out by Cornish (see Thorade, [17]). This fact must 

 he founded in the nature of ocean waves and perhaps it corroborates 

 theoretical results. Taking short crested waves Into account, 

 Jeffreys [l8] could show mathematically that the waves with long 

 stretched crests require a smaller amount of energy from wind for 

 growing than the short crested waves. The long crested waves there- 

 fore have the better chance to grow than the other ones. 



The Intensity of turbulence or the irregular fluctuations of 

 the wind perpendicular to its average direction may be assumed to 

 be nearly of the same order of magnitude as the fluctuations in 

 the average wind direction superimposed on the mean wind velocity. 

 For a sufficiently long time interval, the fluctuations perpen- 

 dicular to the average wind direction and their effects on irregular 

 wave motion probably cancel out, A characteristic wave motion and 

 a significant "sea" therefore will be developed only in the average 

 direction of wind, and this fact seems to be proved by experience 

 at sea. The characteristic "seas" propagate in the direction of 

 the average wind, if we consider undisturbed "wind-seas." The 

 irregularities of wave motion, mostly concerning smaller superim- 

 posed waves, may be considered as "perturbation effects" when deal- 

 ing with the growth of the sea under the action of wind and when 

 trying to comprehend the essential features of ocean waves. But 

 nevertheless, we have to keep in mind that the ocean waves with their 

 limited crests are to be considered strictly as a "three dimensional 

 phenomenon," when going into details. This was shown by Jeffreys 

 (see Thorade [17] » p. 34). 



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