AND OTHER WATER WAVES 291 



on a wave is slight. Thus, such fluctuations of 

 current generally only produce a flicker in the 

 stationary waves, as described in the earliest obser- 

 vations recorded above. But if wave be super- 

 imposed upon wave, the effect of such fluctuation 

 is intensified in a very high ratio. The combination 

 wave may be regarded as a " higher power " of 

 the original quantity, and the effect of an inequality 

 of current as affecting the fluctuation of the com- 

 bined system will increase in a rapid ratio. The 

 fluctuation of a waved wave (as I may term it) 

 is much more sharp and sudden than that of a 

 simple wave. The effect will also be more marked 

 when the standing waves are themselves steep and 

 high relatively to their wave-length. 



Thus the fluctuation of the standing waves of the 

 Whirlpool Rapids becomes sufficiently great for the 

 disengagement of visible travelling waves. The 

 independence of various causes of unequal flow 

 in different parts of the stream makes the travel- 

 ling waves arise independently in different places, 

 and their synchronisms are, therefore, irregularly 

 timed. Great leaping waves are only caused when 

 a number of them (in their resultant drift) converge 

 simultaneously upon a combination standing wave. 



These cross -stream progressive waves do not, 

 however, exhaust the possibilities of progressive 



15 



