AND OTHER WATER WAVES 297 



oi> the bank) was 0.4 second on one occasion and 

 0.7 second on another. The wave-length attains 

 a maximum of about 18 inches or 2, feet before 

 the end of the run is nearly reached. The reason 

 why the waves soon attain a uniform maximum 

 size is that the increase of depth at the crests is 

 accompanied by a corresponding diminution of 

 depth at the troughs where the water becomes too 

 far reduced for further growth. On one occasion 

 I have seen the sudden accession of a little more 

 water (from the passing train) greatly increase the 

 size of the waves. On another occasion, however, 

 near the Glion Station, when much water was 

 poured into the conduit at the end of the journey, 

 the progressive waves vanished altogether. There 

 appeared instead diagonal stationary waves, 

 originating from both sides of the conduit. When 

 the excess of water ran off, the shallower stream 

 ceased to be steady, and again ran in a series of 

 progressive waves. 



The cement floor and sides of the conduit are 

 not, of course, nearly so smooth as the polished 

 marble slab above referred to, but their surface 

 is plain, uniform, and free from palpable excres- 

 cences. The course is straight, and of uniform 

 gradient for considerable distances. The steepness 

 of the gradient is immensely greater than in rivers. 



