AUDITORY JUDGMENTS 627 



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 propaga- 

 tion of sound from a distance, without loss of intensity, through curved con- 

 ducting 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 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 dis- 

 tinguishing 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 tha-t of 

 the impression of the sonorous impulses. 



Binaural Sensations. Corresponding to the double vision of the same 

 object with the two eyes is the double hearing with the two ears; and analo- 

 gous 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 transmitted 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 one 

 ear, two sounds will be heard differing in intensity and tone ; one being con- 

 veyed to the ear through the medium of the atmosphere, the other through 

 the conducting-rod. 



Subjective Sensations. Subjective sounds are the result of a state of irri- 

 tation or excitement of the auditory nerve produced by other causes than 



