Mr. S. P. Thompson on Binaural Audition. 275 



forks, UT3 and MI3, wliicli when struck or bowed together 

 give a well-marked combinational tone, gave none when their 

 sounds were separately led to the two ears. The same was 

 the case with UT3 and SOL-. The effect was not entirely 

 agreeable, being ]3eculiarly harsh, yet unlike any ordinary 

 discord. When MI3 and SOL3 were thus employed together, 

 giving an interval of a minor third, no combinational tone 

 was produced, but the effect was disagreeable and grating in 

 the extreme — a most unpleasant jarring sensation being ex- 

 cited, apparently in the region of the top of the cerebellum. 

 Several observers concurred in the absence of any com- 

 binational tone, and in the unpleasantness of the resultant 

 sensation. 



4. The next experiment was an attempt to ascertain the 

 effect of bringing to the two ears waves of equal pitch and 

 intensity, but differing in phase. A series of more elaborate 

 experiments on this point is still in course of completion ; but 

 before these were begun the following simple experiment was 

 tried. One of my two UT3 forks was loaded until it gave 

 two beats per second with the other. When they were 

 sounded together, there was obviously produced a rapid suc- 

 cession of all possible differences of phase. A slower succes- 

 sion of interferences was afterwards employed. When the 

 two forks were presented separately (and simultaneously) to 

 the two ears, and also Avhen their tones were independently 

 led to the ears by tubes as described above, it was still pos- 

 sible to recognize the fluctuations of tone. There was, how- 

 ever, ro very decided weakening of the intensity of the sound 

 comparable to the "silences" ordinarily observed between 

 the ''beats," the two tones seeming to be going on, but 

 with a difference hardly definable in precise terms. When 

 complete difference of phase was momentarily attained, there 

 seemed to be a slight increase in the intensity of the sound, 

 and the octave note (which, it will be remembered, is not 

 amongst the upper partials of the fork) was faintly heard *. 

 There was, however, no means of demonstrating the existence 

 of such a tone, and the statement rests merely upon the evi- 

 dence of the senses. 



5. It is not easy to explain why interference-beats should 

 thus occur in the simultaneous individual action of the two 

 ears, while combinational tones (difference-tones) are in- 

 audible. There is in the case of the auditory nerves, or 



* It is of some importance to observe that in this experiment the forks 

 were held by assistants, and detached from their resonant boxes, as 

 described in No. 2. 



T2 



