1366 AUDITORY SENSATIONS. [BOOK m. 



various noises ; persons who have great difficulty in detecting dif- 

 ferent notes can often readily recognize differences in noises. 



846. In treating of vision we dwelt at some length on the 

 phenomena of exhaustion which make their appearance when the 

 stimulus is continued. These occur in hearing also, and indeed 

 are indicated by such common phrases as "a deafening noise;" 

 but they are not so prominent as in vision, and do not so distinctly 

 serve as the basis for theoretical discussions. They are best studied 

 by means of musical sounds, since with these owing to their very 

 nature the stimulation is more uniform than with noises. With 

 almost any note, the sensation diminishes and finally disappears if 

 the sound be maintained long enough ; but the exhaustion comes 

 on more rapidly with high than with low notes, especially with 

 very high ones. If a sounding tuning-fork be held up to one ear, 

 and then, just as the sound becomes inaudible be transferred to the 

 other ear, the sound may be distinctly heard; the fresh untired 

 sensory apparatus of the one side is sensitive to the vibrations 

 which the tired apparatus of the other side can no longer feel. 

 Or, if the tuning-fork which the tired ear can no longer hear, 

 be replaced by one vibrating at the moment as far as can be 

 arranged with the same intensity as it, but of distinctly different 

 pitch, this will be heard ; the first tuning-fork only tired certain 

 parts of the sensory apparatus, those affected by vibrations of a 

 certain period characteristic of the pitch of that tuning-fork, but 

 left untired the parts of the sensory apparatus responding to the 

 vibration of other periods, such as those of the second tuning- 

 fork. 



Again, the quality of a note struck on a musical instrument 

 depends as we have seen on the presence of partial tones, having 

 certain relations to the fundamental tone. Now, if immediately 

 before striking a note on an instrument, choosing especially an 

 instrument whose notes are ' rich ' by virtue of the number or 

 prominence of the partial tones, we cause one of the partial tones 

 of the note to be sounded powerfully in the ear, the note when 

 subsequently struck does not possess its full quality; it appears 

 ' thin ' or ' poor.' This is because the previous sounding of the 

 partial tone has tired the particular part of the auditory apparatus 

 with which we hear the partial tone, and in the whole sensation of 

 the subsequent full note the constituent sensation corresponding 

 to that particular partial tone is absent or at least is below its 

 normal intensity. Thus we have in auditory sensations something 

 analogous to the " negative image " of visual sensations. 



We do not in hearing experience a sensation analogous to the 

 visual sensation of white light, a simultaneous stimulation of the 

 apparatus by vibrations of all kinds, and cannot therefore experience 

 an auditory sensation corresponding to the visual sensation of black ; 

 the nearest approach perhaps to such a psychological condition is 

 that in which we are placed upon the sudden cessation of powerful 



