12 PROCEEDINGS OP THE AMERICAN ACADEMY 



upon the ears separately even when the greatest precautions are 

 taken to prevent both from affecting the same ear. (2) Under no 

 circumstances does it seem to be possible to produce differential 

 tones by binaural combination, even when the separate tones are 

 extremely loud. (3) In all cases in which the beating sounds have 

 apparently acted separately upon the auditory apparatus of each ear, 

 the singular phenomenon of encephalic localization of the beats has 

 appeared, while this phenomenon has never been found present 

 either when the two sounds acted simultaneously upon the same ear 

 through the auditory canal, or when one of them was manifestly 

 transmitted to the ear through the bones of the skull. 



We are therefore led to the conclusion that the mechanism in 

 which the interference causing beats takes place, and through the 

 operations of which we consequently recognize the character of con- 

 sonant and dissonant intervals, lies, in part at least, beyond the 

 auditory apparatus of the inner ear. It seems to us clear that notes 

 may beat when they do not affect the same vibrating elements of 

 the inner ear, and that we must look to some more profound changes 

 within the sensorium itself for a complete explanation of the phe- 

 nomena under consideration. 



It may be possible that there are two distinct causes of beating; 

 one, that suggested by Helmholtz, which wholly or principally 

 obtains when the two notes act simultaneously upon the same 

 ear, and the other due to some different and more obscure action 

 which obtains in the case of binaural beats. In this case quite 

 different laws as to consonance might hold. The exceeding harsh- 

 ness of dissonances in binaural audition lends some support to this 

 view. 



Rogers Laboratory or Physics, 

 May, 1891. 



