368 



Mr. C. A. Bell. 



[May 13, 



method would be so laborious as to be impracticable in most circum- 

 stances. 



Tabular forms have been prepared by help of which the computa- 

 tions of the coefficients in the form p cos 0, q sin 0, may conveniently 

 be carried out, with a minimum of arithmetical labour ; also for 

 obtaining the coefficients P and the angle C in the form P sin (6+ C) ; 

 and the method of correcting the coefficients, as computed from the 

 observed quantities, for any non-periodic variation between the com- 

 mencement and end of the series is likewise indicated. 



III. " On the Sympathetic Vibrations of Jets." By Chichester 

 A. Bell, M.B. Communicated by Prof. A. W. William- 

 son, F.R.S. Received April 28, 1886. 



(Abstract.) 



After a brief historical notice of the observations of Savart,. 

 Masson, Sondhauss, Kundt, Laconte, Barret and Tyndall, Decharme, 

 and Neyreneuf, on the sympathetic vibrations of jets and flames, the 

 author describes his own experiments. Attention was directed to the 

 subject by the accidental observation that a pulsating air- jet directed 

 against a flame caused the latter to emit a musical sound. The pitch 

 of this sound depended solely on the rapidity of the jet pulsations,, 

 but its intensity was found to increase in a remarkable way with the 

 distance of the flame from the orifice. In order to study the pheno- 

 menon, air was allowed to escape against the flame from a small orifice 

 in the (diaphragm of an ordinary telephone, the chamber behind the 

 diaphragm being placed in communication with a reservoir of air 

 under gentle pressure. Vibratory motions being then excited in the 

 diaphragm, by means of a battery and a microphone or rheotome in a 

 distant apartment, the discovery was made that speech as well as- 

 musical and other sounds could be quite loudly reproduced from the 

 flame. Certain observations led the author to suspect that motion of 

 the orifice rather than compression of the air in the chamber was the 

 chief agent in the phenomenon ; and, in fact, precisely similar results 

 were obtained when a light glass jet- tube was cemented to a soft iron 

 armature, mounted on a spring in front of the telephone magnet. 



Experiment also showed that an air-jet at suitable pressure directed 

 against a flame repeats all sounds or words uttered in the neigh- 

 bourhood. Except, however, where the impressed vibrations do not 

 differ widely in pitch from the normal vibrations of the jet (dis- 

 covered by Sondhauss and Masson), these effects are likely to escape 

 notice, owing to the inability of the ear to distinguish between the 

 disturbing sounds and their echo -like reproduction from the flame. 



