1886.] 



On the Sympathetic Vibrations of Jets. 



375 



Experiments are given to show that in this instrument the jet may- 

 act upon the electric current in two ways : firstly, by interposing a 

 constantly changing liquid resistance between the electrodes ; and, 

 secondly, by causing changes in the so-called " polarisation " of the 

 electrodes. In one form of instrument, namely, that in which both 

 jet and electrodes are entirely immersed in a mass of liquid of the 

 same kind as the jet liquid, the action must be entirely at the surface 

 of the electrodes. 



In the latter case a liquid jet becomes similar in structure and 

 properties to a jet of air in air, and the velocity at different points 

 when it is steady and when it is disturbed varies in precisely the 

 manner already described. 



The author briefly passes in review the leading facts to be accounted 

 for, and lays stress upon the parallelism of the properties of gaseous 

 and liquid jets. Some shadow photographs of vibrating smoke jets 

 have shown that these also present drop-like swellings and contrac- 

 tions w 7 hich grow along the jet-path. The most satisfactory explana- 

 tion of the phenomena will then be one which refers the vibratory 

 changes in jets of both kinds to the same origin. 



The beautiful and well-known experiments of Plateau have supplied 

 a satisfactory explanation of the normal vibrations of a liquid jet in 

 air. He has shown that a stationary liquid cylinder, whose length 

 exceeds a certain multiple of its diameter, must break up under the 

 influence of the " forces of figure " into shorter cylinders of definite 

 length, which when liberated tend to contract into drops. Now, the 

 jet being regarded as such a stationary cylinder, we have a satisfactory 

 explanation of the musical tone resulting when its discontinuous part 

 strikes upon a stretched membrane, and when the impact disturbances 

 may be in anyway conducted back to the orifice. These disturbances 

 then accelerate the division of the jet after it leaves the orifice. 

 Plateau endeavoured to show that division of the jet might take place 

 at other than the normal points, thus explaining Savart's experimental 

 conclusion that a jet can vibrate in sympathy with a limited range of 

 tones. Lord Rayleigh, moreover, has recently shown that the inferior 

 limit of this range is not so sharply defined theoretically as Savart's 

 experiments would prove it to be. 



Both Savart and Magnus, however, describe experiments in which 

 a water-jet, carefully protected from impact and other disturbances, 

 does not exhibit the peculiar appearances characteristic of rhythmical 

 division ; and the author's experiments conclusively prove that this 

 rhythmical division does not take place in a well insulated jet. While 

 the tendency so to divide may therefore be admitted, and the normal 

 rate of vibration of the jet and its greater sensitiveness to particular 

 tones may thereby be explained, Plateau's theory cannot be held to 

 account for the uniform growth along the jet-path of all changes,. 



