NOT HITHERTO DESCRIBED. 101 



feet from the object which causes it. The reason appears to me 

 •to be, that it is easier to maintain the wave already formed than 

 to form it. I do not believe that it would ever be originally pro- 

 duced at such a distance from a moving body ; but, being already 

 formed at a higher velocity, its existence may be prolonged under cir- 

 cumstances which of themselves would not have given rise to it. 



The third situation in which the wave occurs, as an undulating 

 line amongst the eddies, does not at first sight appear to bear much 

 analogy to those previously mentioned, and I had for many years no- 

 ticed it without any clue to its origin ; but by the light obtained from 

 observations made in the other cases, it was easy to perceive that it 

 was identical in all the three. When there was foam on the river, 

 it was all collected on one side of the little ridge, with a clear strip 

 intervening, and the same checking of the motion of floating particles 

 took place. Although there was no solid body obstructing a stream 

 in this case, there was still water opposing itself to a current, or at 

 least a stream flowing in one direction impeding an eddy setting upon 

 it sidewa} r s. On approaching such a wave with a canoe, one may at 

 once perceive how differently the two sides are affected. If you come 

 down upon it broadside on with the stream, the approach of the canoe 

 has no effect upon it, although }'ou advance quickly enough to make 

 a strong ripple, and you can even pass over it and it re-appears undis- 

 turbed on the other side. But if you approach in the other direc- 

 tion, you cannot get near it at all. If you advance upon it cautiously, 

 you drive it on before you, and if you press it too hard, ripples begin 

 to shew themselves on its further face, and it breaks up and disap- 

 pears. In such situations, by careful handling, I have driven a wave 

 so far as to detach a portion of it from the rest, and have carried it 

 on before me for ten or fifteen yards, whilst, after a while, a new 

 wave was formed in the original situation. This may further illus- 

 trate the remark which I before made, that it is much easier to 

 maintain one of these waves in existence than to form one, for I never 

 succeeded in producing one in calm water with the irregular motion 

 which accompanies the most careful use of the paddle. 



In some cases, where the water boils up from below, you find an 

 irregular circular patch surrounded by one of these waves, and ap- 

 proaching from the outside you may drive it before you till the two 

 sides meet, or by coming upon it end on, you may divide it into two. 

 In this latter case, if it be not very large originally, both the patches 

 will go on rapidly contracting, till they finally run up to a point with 

 a little conical jet ; and if the wave be well marked and your motion 



