364 Scientific Proceedings, Rogal Dublin Society. 



difference-tone may be distinguished when the forks are almost 

 inaudible themselves. 



The theory advanced by Dr. Thomas Young, to explain 

 the difference-tone— at that time called, after its discoverer, 

 " Tartini's beats " — was, that beats, when sufficiently rapid, merged 

 into a musical note, which was heard as an accompaniment of the 

 two beating-tones. This explanation was rejected subsequently, 

 on the ground that mere rapidity of beats would never produce a 

 musical note. 



Perhaps the production of the difference-tone I have described 

 may be an exception to this ; for any note arising from a 

 membrane, played upon by a water- jet, is produced by the 

 impacts of drops. Now, if (in consequence of their being cast off 

 nearer the orifice) any drops or groups of drops strike the 

 membrane with greater momentum than others, at equal intervals, 

 and with sufficient rapidity, the result should be a musical note. 



The quality of this note is rough, and different from the pure 

 clear notes that issue from the membrane when a single fork is 

 used. 



On experimenting with a resonator of the same pitch as the 

 difference-tone, I failed to detect any resonance, and am therefore 

 doubtful as to its existence external to the ear. 



I have so far tried to account for this difference-tone by the 

 periodic impacts of certain drops, but there are other drops 

 between these. 



May it not be that with respect to the general disturbance 

 emitted by the membrane, the ear exercises a selective function, 

 and gives a general impression of a note, roughened perhaps by 

 the presence of the other drops as a disturbing element ? 



These difference-tones may be obtained otherwise than by 

 using two tuning-forks, but not so certainly. If one tuning-fork 

 be used and the jet sung to, they can be produced. A jet of 

 water at suitable pressure will produce a pure clear note from a 

 membrane alone. On now singing to the jet, or sounding an 

 organ-pipe of proper pitch, a difference-tone may be heard. 



In experimenting thus, one is limited in the production of 

 difference-tones, for the jet must be sensitive to both components 

 separately, and thus the interval between them cannot be great. 



I hope soon, if time allows, to examine these differential tones 



