298 WAVES OF THE SEA 



The wave phenomena in the conduit are abso- 

 lutely different from those normal to rapid rivers 

 of considerable depth. In the latter, any cause 

 which retards the flow gives rise to waves stationary 

 as regards the bank, with their steeper face up- 

 stream, and travelling through the water in a direc- 

 tion more or less directly up-stream. In the con- 

 duit, on the contrary, the waves, which have their 

 steep face down -stream, travel through the water 

 down -stream, as I proved by measurements, to be 

 quoted later. In rivers of moderate depths where 

 standing waves arise, the dominant factor in 

 wave-making is pressure, the effects of friction 

 being relatively very small. Thus, where pres- 

 sure is increased, the stream -lines open out and 

 the level of the surface rises, in the manner 

 and for the reasons which have been set forth by 

 many authors who have dealt with the theory of 

 ship-waves. 



The total depth is greater at the crest of the 

 waves, and here the flow is slower ; less at the 

 troughs where the flow is quicker ; and a state 

 of continuous flow is thus maintained, an equal 

 quantity of water passing each cross -section of the 

 river in each unit of time. 



But in the conduit, where the depth is initially 

 very small, the frictional resistance of the bed be- 



