1016 FUNCTIONS OF THE VESTIBULE. [BOOK m. 



movements are started in the auditory epithelium, in more or 

 less complete correspondence with the sets of vibrations which 

 originate from the musical instrument or other sounding body, 

 and admitting further that each set of such molecular move- 

 ments in the auditory epithelium starts a particular nervous 

 impulse in a fibril or in a set of fibrils of the auditory 

 nerve, we are very far from having solved the problem of 

 hearing. 



It must be borne in mind that making the fullest allowance 

 for the assistance afforded us by the organ of Corti, the appre- 

 ciation of any sound is ultimately a psychical act. The analysis 

 of the vibrations by help of the basilar membrane or otherwise 

 is simply preliminary to a synthesis of the auditory impulses so 

 generated into a complex sensation. We do not receive a dis- 

 tinct series of specific auditory impulses resulting in a specific 

 sensation for every possible variation in the wave-length of sono- 

 rous vibrations any more than we receive a distinct series of 

 specific visual impulses for every possible wave-length of lumi- 

 nous vibrations. In each case we have probably a number of 

 primary sensations, from the various mingling of which, in dif- 

 ferent proportions, our varied complex sensations arise; but 

 there is this difference between the eye and the ear that whereas 

 in the former the number of primary sensations appears to be 

 limited to three or at least to six, in the latter the number is 

 probably very large ; what the exact number is has not at pres- 

 ent been even suggested. Our appreciation of a sound is at bot- 

 tom an appreciation of the combined effect produced by the 

 relative intensities to which the primary auditory sensations 

 are, with the help of the organ of Corti, excited by the sound. 

 The appreciation and the subjective analysis of sounds is ulti- 

 mately a psychical process ; and though there are individual 

 differences in the structural finish and physical capabilities of 

 the auditory epithelium as of other parts of the ear, the differ- 

 ences in the psychical or at least cerebral powers of individuals 

 are far greater ; and when we speak of a musical ear we really 

 mean a musical mind or a musical brain. 



631. If the organ of Corti, as appears from the above, 

 affords the means by which we appreciate tones, it is evident 

 that by it also we must be able to estimate loudness, for the 

 quality of a musical sound is dependent on the intensity, as 

 well as on the pitch, of the partial tones in relation to the 

 fundamental tone and to each other. Further, as we said above 

 the distinction between noise and music is a quantitative and 

 fluctuating one ; indeed the tendency of inquiry seems to shew 

 that the quality or timbre of a sound, and it is this which so 

 largely contributes to the value of a sound as an element of 

 music, is in part dependent on vibrations, which being irregular, 

 that is, having no exact arithmetical relation to the fundamental 



