68 Dr. Scott Alison, [Feb. 18, 



the hearing tube and the solid sounding body will suffice for this result. 

 The restriction of hearing to one ear is perfect, although the conditions 

 of the ears and of the two limbs of the differential stethophone are 

 precisely alike, with the exception of the ring of water. As we form 

 our notions of sounding bodies being on our right hand or on our 

 left, by perceiving through which ear auditory sensations are ac- 

 quired, and as water under the circumstances gives an augmentation 

 of soimd sufficient to restrict to one ear, an aural illusion may be 

 produced by having two hearing tubes of equal length and of the same 

 conditions brought in contact with two windows respectively, and 

 placing under the cup of one of them a thin bag of water, which may 

 be called a hydrophone. A church bell or a barrel organ will be 

 heard only through the ear connected with the window having the 

 water bag upon it, although these sounding bodies may be nearer the 

 other window. The mind is led to believe that the sounding bodies 

 are nearer the window which is the more distant from them. 



In the case of some few sounds, the influence of water in modifying 

 their tone is so great, that virtually a sound different in kind is 

 heard. Thus, a watch, in Dr. Alison's possession, gives simply a short 

 ticking sound to that ear connected with one cup of the differential 

 stethophone held in the air ; and imparts a full soft tick, or rather tack, 

 and a musical bell sound to the other ear connected with the other cup 

 of the instrument placed upon the thin bag of water lying on the 

 watch. The sound of the watch is so modified by the different media, 

 that as it were two different sounds are obtained, a sharp tick and a 

 full soft tack, and though the watch-sound is conveyed in greater 

 intensity to one ear than to the other, it is heard in both ears. No loss 

 of sensation takes place, as in the case of the same sounding body, 

 sounding through the same medium. The reason of this exception to 

 the law of auditory obliteration, so to speak, is found in the fact 

 that the sound is no longer one, but has become virtually two, by 

 being conveyed through two different media, and it has been already 

 stated that a major impression sensorially nullifies a minor in the case 

 of its own sound only and of no other. The fine bell sound has been 

 simply made audible by passing through water. It is probable that 

 the double hearing of some persons which has been commented upon by 

 physicians has been due to a difference in the two ears involving a 

 disagreement in the media through which sounds have had to pass. 

 The double hearing referred to has consisted of hearing the sounds of 

 the same sounding body, very different in character in the two ears ; 

 the sounds in one ear being soft and in the other sharp, and so on. 

 Perhaps, likewise, certain sounds inaudible in one ear have been 

 rendered audible in the other, as in the case of the fine bell sound above 

 referred to, by passing through better media. It is to be observed, 

 that in order to have a sensation in this manner in both ears the sound 

 must not preponderate greatly in one. n 



In the case of sounds conveyed to the ear through the bones of the 

 head, a restricting intensity may be procured by closing the aperture of 

 the external ear, as has been observed and commented upon by Mr. 



