units, equation (37) becomes 



L = (3) gT^/27r (53) 



Now suppose that the average speed is computed by assuming that the 

 classical formulas involving the period and the wave length of a simple 

 harmonic progressive wave hold for the average "period" and the 

 average "wave length" of an irregular state of the sea. The results 

 are that 



C=ygT/2Tr (54) 



from equations (51) and (53) and that 



C = gT/27r (55) 



from equation (52). 



The result is two different values for the same theoretical quantity, 



and there is a contradiction involved. The contradiction lies in the 



assumption that the classical formulas can be applied to average wave 

 properties. 



For an irregular sea, current theory tells us nothing about the 

 average wave "speed". Neither equation (54) nor (55) can be assumed 

 to be the correct one. 



2. The Observation of Wave "Speeds" 



Wave crest "speeds" must therefore be observed independently of 

 the "periods" and the "wave lengths". The "speed" of a given crest 

 may not even be a constant. The wave crest "speeds" can be measured 

 at the same time that the "wave lengths" are being measured by the 

 methods given by Pierson, Neumann, and James ( 1955). Such observations 

 in a sea are very scarce, if any exist at all, and thus the present state 

 of theory and observation can give no information on this problem. 

 Data on this problem, when they become available, will prove to be 

 very interesting. 



IV. CONCLUSIONS 



The visual observation of the properties of ocean waves will always 

 be an important supplementary source of wave data. The data thus 

 obtained can never be as adequate as w^ave records v/hich are analyzed 

 for their spectra, but they can be used if they are interpreted with 

 care. 



44 



