MECHANICS OF THE INNER EAR I 23 



alone audible. We see from the table that even now, in ad- 

 dition to 5, the very weak difference tone 3 and the fairly- 

 strong difference tones 2 and 1 are to be expected by the ob- 

 server. 1 



As to the several difference tones, the most favorable con- 

 dition for 6 seems to be, to have the component 5 of the com- 

 pound stirrup movement somewhat more pronounced than 8. 

 It appears, however, that in no case will this difference tone 

 become very conspicuous. The most favorable condition for 

 the difference tone 3 seems to be, to have the component 8 of 

 stirrup movement about as strong as 5. The difference tones 

 2 and 1, on the other hand, appear with a maximum of in- 

 tensity when the component & of stirrup movement is some- 

 what greater than 8. But their intensities are but little less 

 in case the amplitudes of the two stirrup movements 8 and 

 5 are equal. With respect to all the difference tones taken to- 

 gether, it appears that these tones are very unfavorably influ- 

 enced by a considerable difference in the amplitudes of the 

 component stirrup movements, for no difference tone has a 

 maximum intensitv in either the first or the fifth case. And 



1 Although this booklet is devoted to theory and not to experimental 

 methods of research, I cannot refrain from mentioning a way of testing 

 the theoretical results just spoken of, because it is so easy for an3' one who 

 possesses a skillful hand and a trained ear, and the observation to be made 

 is so pretty. No instruments are required but two good tuning forks on 

 resonance boxes, accurately tuned in the ratio of 5:8, and a bass bow. The 

 fork 5 must be sounded first, as strongly as possible, and it is necessary to 

 have a fork which continues to sound strongly for quite a while. Then 

 the bow is applied with the most delicate touch to the fork S. It is neces- 

 sary for the success of the experiment that the intensity of the higher tone 

 vibration be increased from zero very slowly and uniformly. If these con- 

 ditions are fulfilled, one suddenly hears the low difference tones 1 and 2 

 being added distinctly to the tone 5, wherea6 of S no trace is yet audible. 

 If now the fork 8 is left to itself, and the fork 5 is stopped by firmly touch- 

 ing it with a finger, the tone 5 together with the difference tones disap- 

 pears, but immediately one hears with surprising clearness the tone S, which 

 a moment ago was entirely inaudible. No similar observation can be 

 made with a strongly sounding fork S and a weakly sounding fork 5. Ac- 

 cording to our theoretic deduction the lower tone does not become 

 inaudible when the amplitude of 8 is three times that of 5, but still has a 

 respectable intensity. 



