NOT HITHERTO DESCRIBED. 99 



a long way beyond it without check, their motion was at last arrested 

 before reaching the canoe. 



Prom these facts I was induced to conclude that a body propelled 

 through the water at a low velocity, and with an even regular mo- 

 tion, pushes before it a wedge-shaped film of water, the under sur- 

 face of which is not a straight line, but a curve of rapidly increasing 

 curvature ; that, at very low velocities, this film remains unbroken 

 to a distance of several feet ; and that, with increased speed, the 

 distance to which it extends is diminished, whilst its greatest depth 

 remains nearly uniform. There are two things, however, which this 

 supposition will not account for. It will not account for the wave 

 itself: for the film which I have imagined does not appear to extend 

 so far, and under no circumstances did any of the particles, even the 

 smallest, become stationary, till they had passed the wave by about 

 two inches, that interval being always perfectly free from the scum 

 collected. The other circumstance which is left unexplained is, why 

 the feathers and thistle down resting on the water were not also 

 arrested when they came to the film, I do not attempt to account 

 for the difficulty, I only record the facts as I observed them. 



I endeavoured to arrive at some conclusion as to the form and 

 size of the wave, but without much success. Its exceeding minute- 

 ness, the inconvenient position of the observer in the canoe at a 

 considerable distance from it, and that distance constantly changing 

 with the varying force of the wind, made any accurate measurements 

 almost impossible. I therefore had recourse to the second form, in 

 which I have mentioned that it occurs, where, from the similarity of 

 the circumstances, one would expect to meet with the same facts, 

 and which in many respects afforded greater facilities for observa- 

 tion. 



"When the water was high in the river in which I made my obser- 

 vations, a great deal of foam came down from the falls above, and 

 at every projecting tree there was a dense collection of froth, with 

 a clear space intervening between it and the wave. Upon clearing 

 away this froth I could observe its gradual re-formation. It was 

 very curious to watch a small patch of foam sailing down with the 

 current. When it approached very close, and in passing the wave, 

 its velocity seemed momentarily increased, but it was then suddenly 

 arrested, whilst there would shoot out from underneath it bits of 

 sawdust, and other matter that had become entangled in it, which 

 would arrange themselves according to their draught of water in the 

 vacant space between the wave and the log, the foam itself remaining 



