OF ARTS AND SCIENCES. 7 



obtained between notes of very great intervals, there are certain 

 phenomena of binaural audition which appear to prove that this 

 view is incorrect, and that rather than, or at least in addition to, 

 this mechanical interference of vibrations in the ear, there is a more 

 obscure operation within the sensorium itself. I refer to the fact 

 that beats may occur when the exciting sounds operate upon different 

 ears, and also apparently between the after-sensation and the suc- 

 ceeding sound of mistimed unisons. Whether this last phenomenon 

 can be observed when the after-sensation results from an impression 

 made upon the opposite ear to that which is impressed by the suc- 

 ceeding sound, I do not know; but in view of the fact that two 

 simultaneous sounds acting upon different ears may beat, I do 

 not see why this result should not be possible. 



''Now if beats arise between the after-sensation and a following 

 sound, Helmholtz's view can be true only upon the supposition that 

 the vibrating parts of the inner ear continue in motion as long as 

 the after-sensation persists ; and that there is no residual sensation 

 capable of giving beats other than that which persists only as long 

 as the actual vibration in the ear itself continues. Such a. sup- 

 position seems quite improbable. Moreover, the phenomenon of 

 beats in the case of sounds acting simultaneously upon different ears 

 cannot be explained even upon this supposition. There must "be 

 some kind of vibration, using this term in the most general sense, 

 or some kind of alternation of phase or state within the sensorium 

 itself. 



"There is no question as to the fact of the production of beats 

 under the circumstances last mentioned. I have not only verified 

 the fact by experiments conducted in the usual manner, but have 

 also studied the beats produced when a tuning-fork is held close to 

 one ear and the sound of a second fork, not quite in unison with it, 

 is transmitted by telephone to the other, taking suitable precautions 

 that the ear against which the receiving telephone was held was not 

 affected by the sound of the neighboring fork. Beats were readily 

 obtained, which grew weaker as the fork was moved away from the 

 open ear and approached to the ear which was closed by the receiver. 

 The same result occurred when, instead of mistuned unisons, har- 

 monic forks were used, which gave beats with the fundamental." 



In the experiments just cited, the fact that the fork gave feebler 

 beats as it was moved towards the ear to which the telephone was 

 applied seemed clearly to indicate that the beats were not likely to 

 be due to sounds transmitted through the head from one ear to the 



