increases with increasing wind velocity. Observations show 

 that with strong winds high waves will develop in less than 

 12 hours. 



6. Wave velocity and duration of wind . Although observa- 

 tional data are inadequate, it is known that for a given fetch 

 and wind velocity, the wave velocity increases rapidly with time. 



7. Wave steepness . No well established relationship exists 

 between wind velocity and wave steepness, that is, the ratio of 

 wave height to length. This is probably due to the fact that 

 wave steeiDness is not directly related to the Vvlnc velocity, but 

 depends upon the stage of development of the v/ave . The stage of 

 development, or age of the wave , can be conveniently expressed 

 by the ratio of wave velocity to wind velocity (C/U), because 

 during the early stages of their formation the waves are short 

 and travel with a velocity much less than that of the wind, while 

 at later stages the wave velocity may exceed the wind velocity. 

 In order to establish the probable relation between wave steep- 

 ness and wave age all wave observations were examined which 

 appeared to be consistent with certain basic requirements and 

 for which values of H, L ( or £ or T) , and U were recorded. 

 The corresponding values of H/L and C/U were plotted in a dia- 

 gram (fig. 7). The scattering of the values is no greater than 

 "■'ould be expected, considering the great errors of measurements. 

 There appears to be a definite relationship between the steep- 

 ness and the age of the wave. This relationship, shown by the 

 curve in Figure 7, plays an important part in the theoretical 

 discussion. 



16 



