NOT HITHEETO DESCEIBED. 97 



i9, indeed, so minute that it might easily have escaped notice, for 

 under ordinary circumstances it cannot much exceed -^ of an inch 

 in height, and hardly reaches an inch in amplitude. Such an ex- 

 ceedingly minute object may seem scarcely of sufficient interest to 

 form the subject of a paper to be read before the Institute ; and be- 

 ing apparently only a disturbance of the capillary film on the sur- 

 face, -which is subject to very different laws and forces from those 

 which govern the motions of the whole mass of a fluid, it is doubt- 

 less of much inferior importance to the waves which Russell ex- 

 perimented upon. But as no fact is so trifling that it may not assist 

 in establishing correct views of the operations of nature, and as the 

 Institute has invited communications from its members, giving an 

 account of original observations upon all phenomena, I venture to 

 call attention to some curious particulars which I have noticed re- 

 specting this capillary wave, which differs from all others previously 

 described in being a solitary one. 



The wave in question may be observed in three different situa- 

 tions. "Wherever a large body of water, with a strong current, 

 meets comparatively still and deep Avater below, it may always be seen, 

 as a sharply defined line, like a hair upon the surface, winding about 

 amongst the numerous eddies which are formed in such situations, 

 ever varying in its outline, and carried along apparently with the 

 general course of the stream, whilst upon the whole it maintains near- 

 ly the same position. It is also generally to be found where there 

 exists any impediment to a current, as a dead tree projecting out 

 into a river, or a boom thrown across the stream. In this case the 

 wave may be observed at a distance of from one to three feet above 

 the obstacle, the distance varying with the force of the current. 

 The third case is the reverse of the former one, where a body, pro- 

 pelled through still water, pushes this small wave before it. It oc- 

 curs much more rarely under these circumstances, and may more 

 easily elude observation, and since my attention has been attracted 

 to it I have often failed to produce it ; but it was in this form that 

 I first got any insight into its nature. 



Paddling in a canoe in a sheltered bay, with just sufficient air stir- 

 ring overhead, without raising a ripple on the water, to cause the 

 canoe, when abandoned to itself, to drift broadside on at the rate of 

 perhaps half a mile an hour, I perceived the wave in advance of the 

 canoe, at a distance of about three feet. If the wind died away, the 

 wave was maintained at a greater distance, and upon one occasion I 

 could distinctly trace it so far as from between eight and nine feet 



VOL. II. — G 



