7*2 THE SENSES 



sounds, but to render them perceptible, and which is similar in construction 

 to artificial musical instruments, but which far surpasses them in the delicacy 

 as well as the simplicity of its execution. For, while in a piano every string 

 must have a separate hammer by means of which it is sounded, the ear pos- 

 sesses a single hammer of an ingenious form in its ear bones, which can make 

 every string of the organ of Corti sound separately." 



Auditory Judgments. Direction. The power of perceiving the 

 direction of sounds is not a faculty of the sense of hearing itself, but is an act 

 of the mind judging by experience previously acquired. From the modifica- 

 tions which the sensation of sound undergoes according to the direction in 

 which the sound reaches us, the mind infers the position of the sounding 

 body. The only true guide for this inference is the more intense action of the 

 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 prop- 

 agation of sound from a distance, without loss of intensity, through curved 

 conducting tubes filled with air. By means of such tubes, or of solid con- 

 ductors, which convey the sonorous vibrations from their source to a distant 

 resonant body, sounds may be made to appear to orginate 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 being 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 

 impossible to determine whence the sound comes. 



Distance. The judgment of the distance of the source of sounds is in- 

 ferred from their intensity. The sound is interpreted as coming from an 

 exterior sonorous body. When the intensity of the voice is modified in imita- 

 tion 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 judg- 

 ment, when they modulate the voices, and at the same time pretend, them- 

 selves, to hear sounds as coming from a certain direction. 



Duration of the Auditory Stimulus. By removing one or several teeth 

 from the toothed wheel of a vibrator, the fact has been demonstrated that in 

 the case of the auditory organ, as in that of the eye, the sensation continues 

 longer than the impression which causes it; for a removal of the tooth pro- 

 duced no interruption of the sound. The gradual cessation of the sensation 

 of sound renders it difficult to determine its exact duration beyond that of 

 the impression of the sonorous impulses. 



Binaural Sensations. Sound stimulates each of the two ears yet ordi- 

 narily only one sound sensation is perceived, just as in binocular vision 

 ,only a single object is seen. Analogous to the double vision dependent on 



