WAVES 



85 



object during the interval. Continue the observation until at least 15 

 well- formed waves have been timed. 



9223. Add the elapsed times of the various groups together and divide 

 the total by the number of waves to obtain the average period. 



Example: The observer might make the following observation to 

 determine the wave period: 



The wave period 

 15 seconds. 



should be recorded to the nearest second, e.g., as 



9300. WAVE HEIGHT 



9310. GENERAL. The height of a wave is the vertical distance 

 between a crest and the troughs on either side of it (see Fig. 12), The 

 wave height, as recorded on Form 615-5, is the average of the estimated 

 heights of the larger, well- formed waves (see 19002). 



Figure 12. --Wave length and height. 



(1) The wave length (L) is the horizontal distance between successive 



crests, or troughs. 



(2) The height (H) is the vertical distance between crest and trough. 



(3) The wave speed is the distance traveled by a wave in a unit of time. 



(4) The period is the interval of time which elapses between the passage of 



any two successive crests past a fixed point; that is, each crest ad- 

 vances one wave length in a time equal to one period. It is the wave 

 length divided by the wave speed. 



