386 



Royal Society : — 



direct to the ear, I propose to give the results of experiments made 

 with an instrument which I have invented for hearing with both 

 ears respectively, and which, as it is specially adapted for the auscul- 

 tation of differences in the sounds of different parts of the chest, I 

 have named the Differential Stethoscope, or Stethophone. 



The results thus procured will he more satisfactory than those ob- 

 tained by ordinary audition ; a sound will he increased as a visual 

 object is magnified by the microscope, and as both ears are similarly 

 dealt with, a perfect parity of conditions will hold in respect of 

 both ears. 



The differential stethophone (see figure) is simply an instrument con- 

 sisting of two hearing-tubes, or trumpets, or stethoscopes, provided 

 •with collecting-cups and eai'-knobs, one for each ear respectively. The 

 two tubes are, for convenience, mechanically combined, but may 

 be said to be acoustically separate, as care is taken that the sound, 

 once admitted into one tube, is not communicated to the other. The 

 tubes are composed of two parts nearly equal in length, one near the 

 ear-knob, made of metal (C) ; while the other part, near the collecting- 

 Cup, is made of metal wire (B), to impart 

 flexibility. The ear-end is curved, so as 

 to approach the ear, and is supplied with 

 an ivory knob (D) for insertion into the 

 meatus externus. The other end of the 

 tube, being intended to collect sound, is 

 supplied with a hollow cup, or receiver (A) 

 made of wood, or some such material. 

 The mechanical construction of this in- 

 strument is borrowed from the stetho- 

 scope 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 tvv'o 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 



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