102 Off A SMALL CAPILLAET WAVE NOT HITHEETO DESCRIBED. 



pretty swift, at the moment of disappearance there is a drop of water 

 projected into the air. In such instances, when the circle has be- 

 come very small, although the motion is too rapid for any precise 

 observation, it is evident to the eye that the included space is ele- 

 vated above the mean level, which confirms the remark I made when 

 speaking of the shape of the wave. 



I believe I have now mentioned all the facts which I have ascer- 

 tained respecting this apparently insignificant, but in my view very 

 interesting little object, excepting the very different manner in which 

 it is affected by different disturbing causes. As I stated before, if 

 you approach in one direction you may take a canoe over it, and it 

 emerges on the other side unimpaired ; the irregular currents of an 

 eddy have no effect upon it, except to give it an undulating move- 

 ment, and I have seen it maintaining its place amongst the standing 

 waves of a rapid when they have been several inches high. I have 

 even raised considerable swells by rocking a canoe close to it, and it 

 rides over them without disturbance, but the slightest ripple caused 

 by the wind makes it disappear in a moment ; and if spirits of tur- 

 pentine be dropped on the water a little above it, the whole wave is in- 

 stantly obliterated, to a distance apparently far beyond that to 

 which the oily film extends. 



I regret that I can produce no exact numerical data. I made 

 most of these observations some years ago, in the last days of the 

 fall, and whilst I was making preparations for obtaining more precise 

 results the winter overtook me, and before the opening of the water 

 in the spring other avocations interfered with my plans. The points 

 which it appears desirable to ascertain numerically are, the distances 

 of the wave corresponding to different velocities, and the depths to 

 which the film extends at different intervals, also examined at dif- 

 ferent velocities. The question also arises, what change, if any, is 

 caused by the depth to which the object generating the wave ex- 

 tends. Whether it be a pier rising from deep water, or a two-inch 

 plank floating on the surface, I think there will be found little or no 

 difference ; but one would expect that there must be some limit to 

 the draught of water of an obstacle which would raise a wave, cor- 

 responding probably to the greatest depth of the film. I confess 

 that I should like to see the experiment repeated with substances 

 merely resting on the water, without being wetted, for the observa- 

 tions which I made appear to be inexplicable, and I unaccountably 

 omitted to verify them under other circumstances. 



As I may probably have no opportunity of continuing my observa- 

 tions myself, I mention these desiderata in case any other member 

 of the Institute should fall in with my little friend and take any in- 

 terest in the investigation of his history. 



