THE SENSES. 



583 



sound upon one than upon the other ear. But even here there is room 

 for much deception, by the influence of reflexion or resonance, and by 

 the propagation of sound from a distance, without loss of intensity, 

 through curved conducting tubes filled with air. By means of such 

 tubes, or of solid conductors, which convey the sonorous vibrations from 

 their source to a distant resonant body, sounds may be made to appear 

 to originate in a new situation. The direction of sound may also be 

 judged of by means of one ear only; the position of the ear and head be- 

 ing varied, so that the sonorous undulations at one moment fall upon the 

 ear in a perpendicular direction, at another moment obliquely. But 

 when neither of these circumstances can guide us in distinguishing the 

 direction of sound, as when it falls equally upon both ears, its source 

 being, for example, either directly in front or behind us, it becomes im- 

 possible to determine whence the sound comes. 



Distance. The distance of the source of sounds is not recognized by 

 the sense itself, but is inferred from their intensity. The sound itself is 

 always seated but in one place, namely, in our ear; but it is interpreted 

 as coming from an exterior soniferous body. When the intensity of the 

 voice is modified in imitation of the effect of distance, it excites the idea 

 of its originating at a distance. Ventriloquists take advantage of the 

 difficulty with which the direction of sound is recognized, and also the 

 influence of the imagination over our judgment, when they direct their 

 voice in a certain direction, and at the same time pretend, themselves, to 

 hear the sounds as coming from thence. 



The effect of the action of sonorous undulations upon the nerve of 

 hearing, endures somewhat longer than the period during which the un- 

 dulations are passing through the ear. If, however, the impressions of 

 the same sound be very long continued, or constantly repeated for a long 

 time, then the sensation produced may continue for a very long time, 

 more than twelve or twenty-four hours even, after the original cause of 

 the sound has ceased. 



Binaural Sensations. Corresponding to the double vision of the 

 same object with the two eyes, is the double hearing with the two ears; 

 and analogous to the double vision with one eye, dependent on unequal 

 refraction, is the double hearing of a single sound with one ear, owing to 

 the sound coming to the ear through media of unequal conducting power. 

 The first kind of double hearing is very rare; instances of it, however, 

 have been recorded. The second kind, which depends on the unequal 

 conducting power of two media through which the same sound is trans- 

 mitted to the ear, may easily be experienced. If a small bell be sounded 

 in water, while the ears are closed by plugs, and a solid conductor be 

 interposed between the water and the ear, two sounds will be heard dif- 

 fering in intensity and tone; one being conveyed to the ear through the 

 medium of the atmosphere,, the other through the conducting-rod. 



