SENSE OF HEARING. 437 



destitute of what is termed a musical ear ; whilst others are endowed with it 

 in a degree, which is a source of great discomfort to them, since every discord- 

 ant sound is a positive torment. The power of distinguishing the direction 

 of sounds appears to be, in Man, at least, for the most part acquired by habit. 

 It is some time before the infant seems to know anything of the direction of 

 noises, which attract his attention. Now although there can be no question, 

 that this perception is acquired by attention to certain variations in the impres- 

 sion made upon the nerve, through the medium either of the tympanic appa- 

 ratus, or of the bones of the head, yet it is equally evident, that there can be 

 nothing in these variations themselves adequate to excite the idea, and that it 

 must therefore be either intuitive or acquired by habit. This is a considera- 

 tion of some importance, in regard to the similar question as to the sense of 

 Visual direction. In some cases we are probably assisted by the relative in- 

 tensity of the sensations, communicated by the two ears respectively. The 

 idea of the distance of the sonorous body is another acquired perception, de- 

 pending principally upon the loudness or faintness of the sound, when we 

 have no other indications to guide us. In this respect, there is a great simi- 

 larity between the perception of the distance of an object, through the Eye, 

 by its size, and through the Ear, by the intensity of its sound. When we 

 know the size of the object, or are acquainted with the usual intensity of its 

 sound, we can judge of its distance ; and vice versa, when we know its dis- 

 tance, we can at once form an idea of its real from its apparent size, and of 

 its real strength of tone from that which affects our ears. In this manner, 

 the mind may be affected with corresponding deceptions through both senses; 

 thus, in the Phantasmagoria, the figure is gradually diminished whilst its dis- 

 tance remains the same, and it appears to the spectators to recede, the illu- 

 sion being more complete, if its brightness be at the same time diminished; 

 and the effect of a distant full military band gradually approaching, may be 

 alike given by a corresponding crescendo of concealed instruments. It is upon 

 the complete imitation of the conditions which govern our ideas of the intensity 

 and direction, as well as of the character, of sounds, that the deceptions of the 

 Ventriloquist are founded. 



571. Some facts of much interest have lately been ascertained, in regard to 

 an occasional variation in the rapidity of the perception of sensory impres- 

 sions, received through the Eye and through the Ear. These facts are the 

 result of comparisons made amongst different astronomical observers, who 

 may be watching the same visual phenomena, and timing their observations 

 by the same clock ; for it has been remarked, that some persons see the same 

 phenomenon, a third or even half of a second earlier than others. There is 

 no reason to suppose from this, however, that there is any difference in the 

 rate of transmission of the sensory impressions in the two nerves. The fact 

 seems rather to be, that the sensorium does not readily perceive two different 

 impressions with equal distinctness ; and that, when several impressions are 

 made on the nerves at the same time, the mind takes cognizance of one only, 

 or perceives them in succession. When, therefore, both sight and hearing are 

 directed simultaneously to one object, the communication of the impression 

 through one sense will necessarily precede that made by the other. The in- 

 terval between the two sensations is greater in some persons than in others ; 

 for some can receive and be conscious of many impressions, seemingly at 

 the same moment ; whilst in others a perceptible space must elapse. 



572. Amongst other important offices of the power of Hearing, is that of 

 supplying the sensations by which the Voice is regulated. It is well known 

 that those who are born entirely deaf, are also dumb, that is, destitute of the 

 power of forming articulate sounds ; even though not the least defect exist in 

 their organs of voice. Hence it appears that the vocal muscles can only be 



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