1 44 WIND CURRENTS AND WIND WAVES 



which were observed on the coast of the EngUsh Channel on December 29, 

 1898, Cornish points out that prior to the arrival of these breakers a gale 

 had been reported in mid- Atlantic in which the force of the wind had 

 probably exceeded 35 m/sec, which was about 5 m/sec greater than the 

 speed of the waves. He considers it probable that these waves were 

 formed within the area of the gale and traveled for a long distance at their 

 original speed. Waves may nevertheless reach the coast before the 

 arrival of the gale, because the speed at which an atmospheric disturbance 

 travels is, in general, less than the maximum speed of the wind within 

 the disturbance. 



Cornish also points out that in the open ocean the existence of long 

 swells can be completely obscured if shorter waves of greater height are 

 present at the same time. He illustrates his point by means of a graph 

 similar to the one shown in fig. 38. It is here assumed that two waves 

 are present, one long swell, curve A, and one wave, curve B, which has 

 only one third the period of the swell but twice as great an amplitude. 



Fig. 38. Interference between a long swell (A) and a much shorter wave (B). 



By the interference of these two waves the surface takes the appearance 

 shown by the heavy curve, C. In this case an observer would get the 

 impression that the waves present were of the same period as the shortest 

 waves, but of variable height, a phenomenon that is often recorded. The 

 long swell therefore may very well be obscured by shorter waves. 



A number of studies have dealt with the relation between the wind 

 velocity and the maximum wave height, the steepness, and the velocity 

 of progress of the waves. For the correlation of quantities that have not 

 been directly measured, the equations on p. 135 give the theoretical 

 relations between wave velocity and wave length or wave velocity and 

 wave period. 



Cornish's empirical results regarding the highest waves can be sum- 

 marized as follows: 



c = O.SW and ^ = i ^- 



£1 6 



By means of the equations on p. 135, one obtains the relation H = 0.48 W, 

 indicating that the highest wave heights are proportional to the wind 

 velocity. Zimmerman's empirical results are 



L = 10.62i/^ = 3.5517^, 



