201 



pouring in of sound into the ear is less marked, a fact sufficiently in- 

 telligible from the diffusion of sound which must take place outside 

 the ear, when the extremity of the tube is held there, and is not 

 inserted into the meatus. It is therefore obvious that the restriction 

 of hearing to one ear, under the conditions specified, is not due to 

 closure of the meatus externus, the cause of the augmentation of sound 

 in some experiments of Mr. Wheatstone, to be shortly referred to. 



The remarkable phenomenon of the restriction of hearing to one 

 ear, above described, seems not to be without important signification. 

 It holds apparently in virtue of a taw seemingly established for the 

 purpose of enabling man and the lower animals to determine the 

 direction of the same sound, with more accuracy than could be done 

 had a judgment to be formed between the intensity of two similar 

 sensations in the two ears respectively. All source of error is 

 removed by there being only one sensation, although there may be 

 two impressions. This law of a stronger impression in one ear, 

 rendering us unconscious of a weaker, but similar impression in the 

 other, has an analogue, though perhaps an imperfect one, in the 

 sense of touch. Very strong impressions upon one part of the 

 body cause such acute sensations, that minor impressions of the 

 same kind upon another part are frequently not felt, in fact, produce 

 no sensation. 



The only observations bearing upon this law which I have been 

 able to discover, are some by Mr. Wheatstone, in a paper entitled 

 " Experiments on Audition," published in the ' Quarterly Journal of 

 Science, Art, and Literature/ vol. ii. New Series, 1827. These expe- 

 riments are intended to show the augmentation which the sensation 

 of autophonic sound, and the sounds of a tuning-fork applied to the 

 head, acquires when the ear is closed, although the perception of 

 external sounds is diminished. Mr. Wheatstone shows that a vocal 

 sound is heard louder in that ear that is closed, say with the finger, 

 than in the other. He also shows, that the sound of a tuning- folk 

 placed upon the head is heard louder in that ear which is closed than 

 in the other which remains open, even though the tuning-fork may 

 be brought nearer the open ear than the closed one. These experi- 

 ments, Mr. Wheatstone says, prove that " sounds immediately com- 

 municated to the closed meatus externus are very greatly magni- 

 fied ;" and he adds, " it is an obvious inference, that if external 



