PHILOSOPHICAL SOCIETY OF WASHINGTON. 69 



The first paper was by Mr. Bell on the subject of 



BINAURAL ALDITION. 

 (abstract.) 



While in England, in 1878, it occurred to Mr. Bell that all 

 the peculiarities of binaural hearing might be produced artificially 

 by the telephone, as the peculiarities of binocular vision are pro- 

 duced by the stereoscope. 



Two transmitting telephones were arranged so that the dia- 

 phragms of the instruments were about as far apart, and occu- 

 pied about the same position relatively to one another, as the 

 drum membranes of a person's ears. These transmitters were 

 connected by two distinct and independent circuits to two re- 

 ceiving telephones, which were placed respectively to the rin;ht 

 and left ears of an observer in a distant place. 



When sounds were made in the neighborhood of the trans- 

 mitting telephones the auditory sensations experienced by the 

 observer in the distant place were of a decidedly novel character. 

 The direction of the speaker's voice from the transmitting tele- 

 phones could be perceived to a limited extent. 



Attempts were made to have the observer determine by ear 

 the exact location of the original sound, with the following 

 result: — 



Imagine the transmitting telephones to be placed in the in- 

 terior of a globe upon which the usual meridian lines and paral- 

 lels of latitude are marked so that the axis of the globe passes 

 yertically through the centres of both diaphragms. 



Sow, suppose we produce a sound at some point in the neigh- 

 borhood of the transmitting telephones — we can take its bearings 

 upon the surface of our globe — we can give as it were ihe lati- 

 tude and longitude of the sound. 



It was found, as the result of a large number of experiments, 

 that ihe distant observer could tell vyith approximate accuracy 

 the latitude of the sound, hut that he had no idea vjhatever of the 

 longitude. 



It then occurred to Mr. Bell that the telephone might be used 

 to test whether the same law held good for direct audition. 



A number of telephones were suspended in different parts of a 

 summer-house, and were connected by independent wires to a 

 common switch-board, so that any desired telephone could be 

 instantly connected with a distant rheotome and battery ?jy the 

 operator at the switch-board. 



The rheotome interrupted the battery circuit about one hun- 

 dred times per second, and a loud musical note was emitted by 

 the telephone which happened to be in circuit with it. 



An observer stationed in the centre of the summer-house was 

 required to indicate by pointing, the exact location of the tele- 

 phone from which the sound proceeded. He was not allowed to 



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