MECHANICS OF THE INNER EAR I3I 



it is in contact on one side with a practically unyielding body, 

 on the opposite side with the easily yielding air. 



It is of the utmost importance, therefore, if we wish to 

 develop the theory by experimental investigation, to keep 

 free from the delusion that any of the above theoretic results, 

 say, in the case of the combination 5 and 8 with equal ampli- 

 tudes, applies to what we hear in case two tuning forks of the 

 vibration ratio 5 : 8, standing at an arbitrary distance from 

 our ears and from the reflecting walls of our laboratory, vi- 

 brate with equal amplitudes. It is only by way of approxima- 

 tion that we can derive any theoretic conclusion from such an 

 experiment. The starting point of our theory is the form of 

 movement of the stirrup, not of external sounding bodies. 



Under ordinary conditions, it is a great advantage that we 

 possess two organs of hearing, some distance apart. In ex- 

 perimental investigations, however, for the 

 The duality of development of a theory of audition, this 

 our auditory f^ct is often a serious obstacle. Since we 



organ cannot make experiments on audition while 



soaring like an eagle, any source of sound 

 is likely to surround our body with standing waves, resulting 

 from reflection. Let us regard the velocity of sound as three 

 hundred and thirty meters, the distance between our ears as 

 about fifteen centimeters. A tone of five hundred and fifty 

 complete vibrations, that is, a tone representing the ordi- 

 nary human voice quite well, has therefore a wave length of 

 about sixty centimeters. The distance between a nodal point, 

 where the rhythmic density changes of the air occur with full 

 intensity, and a point of maximum vibratory movement, where 

 there are practically no density changes affecting the tympa- 

 num, is then about fifteen centimeters. That is, it might 

 happen with standing waves — if the head was kept perfectly 

 still — that the amplitude of one of the components of stirrup 

 movement would be almost zero in one ear, but very large in 



