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sounds can be communicated to act on the cavity in a similar man- 

 ner, they must receive a corresponding augmentation." 



This distinguished philosopher constructed the instrument named 

 a Microphone, for the purpose of augmenting weak sounds upon this 

 principle, i. e. the augmentation of sound by closure of the ears ; 

 and he informs us that it " is calculated for hearing sounds when it 

 is in immediate contact with sonorous bodies," and that "when they 

 are diffused by their transmission through the air, this instrument 

 will not afford the slightest assistance" This instrument is spoken 

 of in connexion with the augmentation of sound, and not in reference 

 to the limitation of sound to one ear, or to the comparison of sensa- 

 tions in the two ears. The remarkable, and, to the uninitiated mind, 

 the wonderful fact, made known more than thirty years ago by 

 Mr. Wheatstone, that a tuning-fork held upon the head close to an 

 open ear is not heard in this ear, but in the opposite ear, provided it 

 be closed with the finger, or by some other means, proved that 

 sounds communicated to the skull were exclusively heard in the 

 closed ear. In the case of the tuning-fork, the fact made known by 

 Mr. Wheatstone is undoubted. The rationale of the phenomenon 

 appears to be this : The vibrations of the tuning-fork are commu- 

 nicated to the bones of the head, and through them to the ears, 

 including their bones, cartilages, and contained air ; but in the case 

 of the closed ear, the vibrations are permitted no egress or escape, 

 as in 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. When 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. Wheatstone' s interesting observation relates to a head-sound 

 not duly 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- 



