Chapter I. 



The composite natiire of wind generated waves 

 according to observations 



1) Comments on observations 



It seems very difficult to define a distinct wave motion at 

 the sea surface, because of the composite pattern of the "sea," as 

 the undulatory motion of the sea surface in the case of wind-driven 

 waves is called by seamen. Besides the wind-driven sea it is possible 

 that one or more different types of swell are running across or in 

 the same direction as the waves generated by the local wind, which 

 fact further complicates the resultant wave motion and therefore the 

 observations at a given locality. The swell is not causally con- 

 nected with the local wind, and this report does not take into ac- 

 count its behavior when travelling over long distances at sea. The 

 discussion at first pertains only to waves under the direct action 

 of wind, considering the matured state as well as the state of wave 

 development. Therefore when trying to observe wind generated waves 

 we have to eliminate, if necessary, in the best possible manner any 

 swell that appears. Sometimes this separation seems very difficult, 

 especially when taking mechanical wave records, like the recent wave 

 records of H, R. Seiwell [10]. They were obtained by automatic re- 

 cordings of wave pressure variations at the sea bottom. The results 

 of H. R. Seiwell obtained by application of the principles of general- 

 ized harmonic analysis to such oceanic wave observations, and the con- 

 clusions drawn from the mathematical treatments — as far as they have 

 been published to this date — may be summarized after H. R. Seiwell 

 and G. P. Wadsworth [11] as follows: 



