42 



Observations and Measurements of Ocean Waves 



show the deviation to be expected from the theoretical values. Figure 25 

 gives the ratio between the wave length A and the wave velocity c, Fig. 26 

 gives the ratio between wave length I and period T. Each point corresponds 

 to a group of observations made by nine investigators. The solid curve 



18 

 16 

 14 

 12 

 » io 



1 8 



<5 



1 6 

 4 

 2 



40 



80 



200 



240 



280 



120 160 



Length Z. , m 



Fig. 26. Wave length and period of ocean waves (Zimmermann). 



corresponds in both cases to the theoretical ratio between the two values. 

 In general, observations agree well with the theory. The 143 observations 

 made in 1914, at the suggestion of Zimmermann, by naval officers on German 

 steamers show that only in eight cases values beyond the interval of 1-55 

 and 1 -57 were found for the formula c = \ 56T. A very good comparison 

 between observations and theories has been given by Thorade in Table 3, 

 based on observations by Paris (1871, p. Ill), Abercromby (1888, p. 263), 

 Schott (1893, p. 82) and Grassenmager (1896, p. 190). 



In this table are given for each group the wave velocities c x respectively c T , 

 which were computed from the observed wave length A and from the observed 

 period T. Furthermore, the ratios c:c ; and c:c T in per cent in which c 

 represents the observed velocity. The values are very close to 100%, which 

 is much better than can be expected from such heterogeneous observations. 

 Therefore, we can state that the equations previously mentioned have been 

 successfully tested by the observations. There is not much sense in discussing 

 extreme values for velocity, length and period of the waves, because it all 

 depends on the time at which a wave is observed. We might mention the 

 very big waves which have a length of 250-350 m and even up to 450 m; 

 with periods varying from 17 to 20 sec and with velocities of propagation 

 from 25 to 30 m/sec (Larisch, 1925). It has been established that wave 

 heights from 10 to 12 m are not exceptional, and extremely high waves from 



