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receiver (A) made of wood, or some such material. The mechanical 

 construction of this instrument is borrowed from the stethoscope 

 contrived by Dr. Caman of New York, and intended by its inventor 

 for the purpose of hearing with both ears 

 sounds emanating from one point, and 

 collected into one cup. The two tubes 

 are brought near together, a few inches 

 in front of the face, by means of a con- 

 necting-bar (E), but calculated to prevent 

 the transmission of sound from one tube to 

 the other. This bar is supplied with a 

 joint, which permits the tubes to be freely 

 moved, as is necessary in applying the 

 knobs to the ears. The two knobs are 

 kept steadily in the ears by means of an 

 elastic band (F) connecting the two tubes 

 near the bar, already described. 



The instrument being fitted into the 

 ears, with the knobs directed upwards, 

 and the cups being applied equally near 

 to, or upon a sounding body, say the in- 

 flating lung, or a watch, and the condi- 

 tions for collecting sound being the same, 

 the sound is heard with both ears, as in 

 ordinary hearing. But if one cup be re- 

 moved a little, say a half or a quarter of 

 an inch from the watch (for we shall now 



adopt it), and the other cup be left upon the watch, the sound is heard 

 with that ear only which is connected with the cup placed upon the 

 watch, and the sensation in the hearing ear is so marked, as to leave 

 the mind in no doubt whatever that it is through that ear we become 

 conscious of the sound. If the cup placed upon or nearer the watch, 

 be removed a little further than the other cup, so as to be less favour- 

 ably situated for collecting sound, say one inch from the watch, the 

 ear connected with it becomes totally unconscious of sound, and the 

 sensation of hearing is most unequivocally felt in the ear, and in that 

 ear only, which but a moment before was utterly deaf to it. If one 



