CHAPTER XII 



The sounds of running water The gushing motion of cataracts 

 Conical structures produced by the break-up of a water- 

 fall The wave-track of a ship. 



On the Sounds of Running Water 



WHEN we watch the standing waves of a shallow 

 stream and think, perhaps, of the steady state 

 to which it is supposed to have attained, the 

 pleasant but irregular sounds which greet the ear 

 are evidence of momentary variations in this state, 

 and of disturbances passing down-stream. The 

 sound of the foaming cusped wave, if continuous, 

 would, indeed, indicate a steady condition, although 

 the motion at that spot is " discontinuous " in the 

 sense that the thread of the stream is there broken ; 

 but the breaking of the cusped wave is, as a rule, 

 intermittent. From time to time also a pretty tinkle 

 catches the ear, a single sound, presently repeated 

 in another place. A careful study of these sounds 

 will greatly assist the eye in discovering the details 

 of the stream's motion. It is upon the sounds as 



