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XXIV. Acoustical Observations. — V. By Lord Rayleigh, 

 D.C.L., F.R.S., Cavendish Professor of Experimental 

 Physics in the University of Cambridge *. 



[Plate IV.] 



Smoke-jets by Intermittent Vision. — Smoke-jets and Resonators. — 

 Jets of Coloured Liquid. — Influence of Viscosity. 



Smoke-jets by Intermittent Vision, 



IN the second series of these observations (Phil. Mag. March 

 1879) I proved that when stationary sonorous waves 

 occupy the region surrounding a sensitive flame, the action 

 of sound in causing the flame to flare manifests itself when 

 the burner is situated at a loop, but not when the burner is 

 situated at a node; from which we infer that the effects are 

 due to a lateral disturbance causing the issuing jet to bend 

 from its course. During the same year I made a stroboscopic 

 examination of a jet of phosphorus-smoke issuing from a 

 draw r n-out glass nozzle, and disturbed by the neighbourhood 

 of a vibrating tuning-fork of pitch 256. So much light is 

 necessarily lost in this method of observation, that some pre- 

 caution is required in illuminating the jet. Two points should 

 be especially attended to. In the first place, the eye must be 

 so situated that the scattered light by which the jet is seen is 

 but slightly deflected from its original course; and, secondly, 

 the background must be thoroughly dark. By carrying out 

 adequately this system of illumination, and by so choosing 

 the revolving disk that the apertures bore a not too small pro- 

 portion to the entire circumference, I was able to see tolerably 

 well by the light of a good gas-flame. When the coincidence 

 of periods was nearly approached, the serpentine motion of 

 the jet previous to rupture was clearly observable. By placing 

 the nozzle exactly in the plane of symmetry between the 

 prongs of the fork, the law above stated could be confirmed. 

 In this position there was but little effect; but the slightest 

 displacement caused an early rupture. 



Smoke-jets and Resonators. 



In order to exalt the sensitiveness of jets to notes of mode- 

 rate pitch, I found the use of resonators advantageous. These 

 may be of Helmholtz's pattern; but suitably selected wide- 

 mouth bottles answer the purpose. What is essential is that 

 the jet should issue from the nozzle in the region of rapid 

 reciprocating motion at the mouth of the resonator, and in a 



* Communicated by the Author. 



