393 Royal Society : — 



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 sounds, 

 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 otlier 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 

 car. The greater intensity of each watch-sound in one ear iias 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 

 watches, the same result follows ; and it is the same if instead of two 

 arms of the stethophone we employ only one. This remarkable 

 separation of the components of a sound may be effected also when 

 the sounding bodies are enclosed in a box capable of transmitting 

 sound, or when separated from us by the interposition of materials 

 capable of conducting sound ; and by successive trials and comparisons 

 of intensity at different places, and by a process of exclusion of those 

 parts which fail to cause sensation, the respective positions of two 

 adjacent sounding bodies may be predicated. If, for example, we have 

 two watches, A and B, enclosed in a box, and through one cup. A, 

 we hear watch A, and with the other cup, B, we hear watch B, we 

 may conclude that cup A is nearer watch A than cup B is, and so on. 

 In the same manner we may auscultate the morbid sounds of the heart. 

 By cup A, placed at the apex, and cup B placed at the base, we hear 

 separately the morbid sounds of the two parts, — for example, a blow- 

 ing murmur at the apex in one ear, and a rasphig murmur at the 

 base in the other ear. This we are enabled to do, although at any 

 intermediate point with the single ear, either with or without a 

 stethoscope, we hear the conjoined two sounds. It is obvious that 

 with the stethophone we not only succeed in separating sound, but 

 that this instrument, or some similar contrivance, affords the only 



