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

 under 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 Royal Society 

 differs from this well-known and readily admitted fact in this im- 

 portant particular, 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 ear 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 more favoured ear increases in a ratio with the increase of sound 

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

 nearly the same, 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 

 placed on a table equidistant from both ears. The stethophone is 

 applied 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 

 inches. As the further cup is brought nearer and nearer the watch, 

 the sound, always confined to the more favoured ear, is gradually and 

 steadily intensified, until the two cups are, or are about to be, similarly 



