AND OTHER WATER WAVES 305 



hollowed piece of pavement, it can be seen to flow 

 gushingly, for the greater regularity of cross - 

 section to some extent co-ordinates the flickerings, 

 and the smaller depth tends to increase the gushi- 

 ness of flow, as has already been explained. 



At the entrance to, and for the first few yards 

 of, the rectangular, flat-bottomed, paved channel 

 these embryo roll -waves pass the eye in too rapid 

 succession to be accurately counted, but there are 

 about 1 20 per minute. They are here little more 

 than ripples, and the fronts, which face down- 

 stream, are free from white froth. As we walk 

 down the bank of the conduit, we observe that a 

 regularising process is at work, which, in a short 

 distance, produces from this hurried and con- 

 fused crowd of progressive wavelets an ordered 

 series of roll -waves of greater amplitude, with 

 foaming fronts facing down -stream, extending 

 across the channel in a straight line at right angles 

 to its axis. On June 6, 1904, at 465 feet from, 

 the entrance to the paved channel, there were 

 notable larger waves ; but there were many minor 

 ones also, and the appearance was still somewhat 

 confused. At a distance of 567 feet from the 

 entrance to the paved channel there was no more 

 confusion, a distinct series of waves, 33 per 

 minute, passing the observer ; whilst after travel- 



