556 



Proceedings of the British Association. 



Velocity of moving point. Number of Waves. 



Feet per min. in an inch. 



55 2 



60 3 



65 4 



72 5 



80 6 



90 7 



103 8 



120 9 



These waves were examples of capillary waves, not in free but 

 constrained motion. He had generated them in a different manner, 

 so as to examine them in free motion, uninfluenced by the generating 

 point, and found that the capillary waves, when moving freely, have a 

 constant velocity of 8£ inches per second, that their duration is short, 

 becoming insensible in about twelve seconds after describing a path 

 not longer than eight or nine feet: in the free state, their breadth 

 is very small at first, gradually increases, and just before vanishing 

 attains an amplitude of nearly an inch. The capillary waves are among 

 the phenomena we most frequently observe. It is in generating them 

 that a gentle breeze forming over the surface of a smooth lake destroys 

 the translucent and reflective power of the surface; they are also to 

 be observed in all cases of primary and secondary wave motion, when 

 the superficial film is by any cause compressed, so as to produce corruga- 

 tion, and they always disappear in about twelve seconds after the excit- 

 ing cause is removed. The second order of waves had also been made 

 the subject of careful observation. A mode had been discovered of 

 generating these waves in large groups, so that instead of observing 

 single waves, the length of one could be deduced from the measured 

 length of a number, thus getting the advantage of repetition of the 

 quantity observed. It had thus been finally determined, that these 

 oscillating waves follow Newton's law in so far that the velocities of 

 transmission are as the square roots of the amplitudes ; but the absolute 

 velocity differs from that of Newton, so that, instead of having the 

 wave whose period is a second of an amplitude =3.26, it is found 

 to be =3.57. The velocities determined are as follows : — 



Velocity of transmission 



of wave. Amplitude. 



Feet per second. Feet. 



3.01 2.65 



3.16 2.94 



3.29 3.125 



