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impaired by the bell. A whistling lung-sqund heard in one ear, is 

 not rendered less obvious by a loud blowing lung-sound in the other. 

 A hissing murmur at the apex of the heart conveyed into one ear, 

 and a rasping sound at the base conveyed into the other, are both 

 heard without alteration in the ears to which they are respectively 

 conveyed . 



By virtue of these two laws, 1st, that sounds of the same cha- 

 racter are restricted to that ear into which they are conveyed in 

 greater intensity, and 2nd, that sounds differing in character may 

 be heard at the same time in the two ears respectively, even if they 

 be made to reach the ears in different degrees of intensity, it is pos- 

 sible to analyse a compound sound, or one composed of two sound?, 

 and to divide it into its component parts. In order to effect a divi- 

 sion of a compound sound, it is only necessary that the two sounds 

 of which it is composed may respectively be heard at certain points, 

 in greater and lesser intensity, and that the respective cups of the 

 stethophone be placed at these points. The ear connected with the 

 cup placed where one half of the sound is in greater intensity, hears 

 that half sound only, and the ear connected with the cup placed 

 where the other half of the sound is in greater intensity, hears that 

 half sound only. The sound is divided into two parts, and one is 

 heard in one ear, and the other part in the other ear. For example, 

 a compound sound composed of the two sounds of two watches 

 placed together upon a table, with the unassisted ear is distinctly 

 heard in its compound state, and cannot be divided into its 

 two constituent parts. With the stethophone this is readily done. 

 One cup is placed where the sound of one watch is in greater in- 

 tensity, and the other is placed where the sound of the other watch 

 is in greater intensity, and the result is obtained of one watch only 

 ticking in one ear, and of the other watch only ticking in the other 

 ear. The greater intensity of each watch-sound in one ear has ren- 

 dered all hearing of it in the other ear impossible, and as each watch- 

 sound in its greater intensity is conveyed to different ears, one is 

 heard in one ear only, while the other is heard in the other ear 

 only. Without the stethophone, or some such instrument, this 

 analysis could not be made ; the ordinary stethoscope will not suc- 

 ceed, for wherever it is placed it conveys the mixed or compound 

 sound to the ear. If the naked ear be applied over or upon the 



