tinues, the sea surface pattern changes its appearance considerably. 

 Symptoms of fully or nearly fully developed sea are striking fluct- 

 uations of wave heights and periods, groups of waves and the occur- 

 rence of outsize waves with long stretched crests. In stormy 

 weather the sea begins to "roll." 



To all appearance longer waves emerge at the rough sea surface 

 probably independent of the fully arisen p -waves, and distinguished 

 by lesser steepness but with propagation velocities which may exceed 

 the wind velocity. By interference of these wave systems typical 

 phenomena of complex wave motion result. 



In Chapter I, an attempt was made to explain the observed strik- 

 ing fluctuations of wave periods and heights In the complex wave 

 pattern by coincidence of three characteristic waves, called the 

 "sea," the "intermediate wave" and the "longer wave." In the fol- 

 lowing discussions these dominating waves may also be noticed by their 

 "ages," that is, by the ratio "phase velocity : wind velocity" in 

 fiilly arisen state, that is "B -wave," "p(l)-wave" and "S *-wave." 

 It seems probable that in the mixture of wind generated ocean waves 

 certain undulations are favored by the wind with respect to the energy 

 transfer. They have a maximum growth, and having attained their 

 maximum values of height and length, they are maintained by a steady 

 energy supply as long as the wind remains unaltered. 



The first characteristic wave, the relatively steep S -wave 

 travels with a phase velocity, that is always slower than the wind 

 velocity. Probably we have to presuppose the existence of these 

 waves, in order that longer waves with a higher amount of energy, 

 and faster than the wind can be generated. The short but steep p - 

 waves cause, with superimposed smaller waves, the broken appearance 



85 



