MECHANICS OF THE INNER EAR I 33 



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 3 and 1 are to be expected by the ob- 

 server/ 



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 5' 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 intensity in either the first or the fifth case. And 



'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 anj' 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 8. 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 i and 2 

 being added distinctly to the tone 5, whereas of 8 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 8, which 

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

 made with a strongly sounding fork 8 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. 



