and growing up of single waves on the other end is a fact well 

 known from observation of the sea. But besides this, there are 

 other waves which change their form much more slowly, as indicated 

 by the wave placed at x = 550 m (B) at the time t = 0. When it 

 progresses a distance of 280 m, we find this wave after 21 seconds 

 only slightly changed in the crest b^. 



If we should observe the wave motion at the point B (x = 550 m 

 on the distance scale in Fig. 8) we should get the "wave record" 

 (b) represented in Fig, 7 (the lower one). After passing the wave 

 crest b, at t = the next crest (b,') follows 8 seconds later, 

 slightly higher than the preceding one. The next wave would be 

 the wave with the crest a., , but this wave almost disappears in the 

 following broad trough and in many cases it will not be possible 

 to recognize this intermittent wave. At the time t = 23 sec the 

 next high wave crest, ag* passes the locality of observation. The 

 "period" between b^^' and ^2 or the time interval between these two 

 striking waves is 14,8 seconds. Waves like these occur rather 

 often in the composite surface pattern of waves and may be called 

 "double-waves" [9]. In all cases the scattering of periods of suc- 

 ceeding waves and the continuous variations of the shape of wave 

 profiles in rather short time intervals are striking features of 

 ocean waves. 



Similar wave profiles like those in Fig, 8 are represented 

 in Fig. 9 at a wind velocity of 19 m/sec. Within the relatively 

 short time of 21 seconds the "wave group" between points A and B 

 changes its shape considerably when progressing a distance of about 

 350 m. At t ss we find a group of waves between x = 500 m and 



32 



