[ 360 



XXXII. 



ON THE STKUCTURE OF WATER- JETS, AND THE EFFECT 

 OF SOUND THEREON. PART II. By PHILIP E. BELAS, 

 A.R.C.Sc.I. WITH NOTE ON COMBINATION-TONES BY 

 PROFESSOR W. F. BARRETT, F.R.S. 



[Plate XXXIV.] 



(communicated by pbofessob w. p. babbett, f.b.s.) 

 [Eead, March 21 ; Received for Publication, March 24 ; Published, June 9, 1905.] 



In a former Paper 1 I described some experiments, showing the 

 effect of periodic vibrations upon a jet of water flowing from a 

 glass tube, and amongst others, one in which a difference-tone 

 was produced by the vibration of a parchment membrane, on 

 which the jet of water impinged when it was influenced by two 

 tuning-forks of different pitches sounded together. 



My attention was first drawn to this combinational tone in the 

 following way : — Shortly after his discovery of sensitive flames, 

 Professor Barrett noticed that a flame occasionally and audibly 

 reproduces the note by which it was affected. While I was 

 assisting him to prepare some experiments for a lecture on the 

 subject before this Society, we noticed that when such a flame was 

 excited by two tuning-forks bowed simultaneously, the note it 

 emitted was the difference-tone. On trying the experiment upon 

 a jet of water, I obtained a similar result. The tuning-forks 

 used were ones making, respectively, 384 and 512 vibrations per 

 second, and the pitch of the difference-tone was therefore 128. 



The object of this Paper is to describe some further observa- 

 tions upon this phenomenon, and to suggest an explanation of it. 



It first occurred to me that, as a membrane was used, the 

 difference-tone produced in this way might be caused by the 



1 Scientific Proceedings, Eoyal Dublin Society, vol. x. (N.S.), Part ii., No. 22. 



