390 Royal Society : — 



as iu the open ear ; reverberations take place, and the consequence 

 is, that the sound is not duly moderated ; and in virtue of the law 

 I have just enunciated, the sensation of sound is restricted to the 

 closed ear. T\'heu the tuning-fork, duly sounding, is held in the air, 

 and not connected directly with the head, the closed ear remains 

 insensible to it, and the sound is heard exclusively in the open ear. 



Mr. AVheatstone's interesting observation relates to a head-sound 

 not dulv moderated, as in the opposite and open ear, and virtually 

 more intense, and comes within the general law advanced in this 

 paper, which embraces all sounds, whether internal or external, viz. 

 that a sound of the same character in the presence of both ears, if 

 conveyed by any means to one ear, or to the nerve of that ear, more 

 intensely than to the other, is heard in the more favoured ear only. 



It seems necessary, in Mr. Wheatstone's experiments, that the bones 

 of the head shall vibrate freely ; weak sounds, such as gentle blow- 

 ing, will not succeed ; and if the tuning-fork be placed immediately 

 inider the open ear, and passed upon the soft parts (little fitted for 

 vibration) between the mastoid process of the temporal bone and the 

 lower jaw, the sound is heard in this ear, and not in the closed ear. 



It may perhaps be well, before proceeding further, to acknow- 

 ledge that I am well aware it has been long known that a very loud 

 sound conveyed into one ear will render the other ear insensible to 

 sound of a weak or low character. But the phenomenon which I 

 have ventured to bring under the consideration of the Iloyal Society 

 differs from this well-know-n and readily admitted fact in this im- 

 portant pai'ticular, that no very great loudness is required, and that 

 no very great augmentation of sound in one ear over that in the 

 other is necessary in order to restrict the sense of hearing to one ear, 

 and to deprive the less favoured ear of the sense of hearing which it 

 had previously enjoyed. A moderate, yet a decided increase of in- 

 tensity is all that is required to remove the sense of hearing from the 

 less favoured ear, and to cause the more favoured organ to be alone 

 sensible to the sound. 



When sound is proceeding into the two ears, but in consequence 

 of its reaching one car in greater intensity than the other is heard 

 only in one ear, the sensation of hearing in the favoured ear, though 

 strictly limited to it, is augmented by the sound entering the less 

 favoured ear, although it entirely fails to cause a sensation there, or 

 to produce a consciousness of sound in that organ. The more sound 

 collected by the less favoured ear, as long as the amount is less than 

 that conveyed to the other ear, the more the sensation of sound is 

 augmented in the more favoured ear. The intensity of sensation in 

 the mere favoured ear increases in a ratio with the increase of sound 

 in the less favoured car, until the intensity of sound is the same, or 

 nearly the sam.e, in both ears, when the sensation experienced is the 

 ordinary one of hearing with two ears. 



This fact admits of satisfactory proof in this way : — A watch is 

 ])laced on a table equidistant from both ears. The stethophone is 

 a])plied to the ears ; one cup is placed within an inch of the watch, 

 while the other is turned away from it, at the distance of some 



