108 Generation, Growth and Propagation of Waves 



spectrum of the wind generated sea; then it is possible to compute the structure 

 of the swell at any place. With increasing distance between P and the wave 

 source the frequency band and the scope of the direction of the swell will 

 become narrower, the crests longer and the periods more uniform. Therefore, 

 the principal features of "old swells" can be easily understood. This theory 

 by Pierson, Neumann and James seems to give a correct interpretation of 

 the development of swells and, together with the above considerations, will 

 give an insight into this kind of ocean waves. 



