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AYERS. [Vol. VI . 



process of combination, which takes place in other organs. The 

 fundamental tone, and each of the harmonics severally, irritate 

 a distinct nerve fibre, and each nerve fibre transmits its irrita- 

 tion separately to the brain. Here, however, where the myste- 

 rious processes of sensation take place, the several sensations 

 are, in an equally incomprehensible isic) manner, combined into 

 a general one, which gives rise to the sensation of a compound 

 tone. Our perception, therefore, of tones of different pitch is 

 produced entirely by an irritation of different fibres of the audi- 

 tory nerve. Through the auditory nerve the brain receives from 

 different fibres an intimation of tones of different pitch, which 

 intimation enables it to distinguish the sympathetic vibratory 

 oro'ans which have answered to the tone." 



o 



It does not follow that because one is able under certain con- 

 ditions, as by the use of resonators, careful attention, and 

 selected experiments, to hear overtones and audibly prove their 

 presence in company with a fundamental, that such an overtone 

 modifies the quality of the fundamental tone unless it is strong 

 enough to produce a discrete set of undulations in the hair 

 band, and all undulations of the air, whether they are overtones 

 or not, unless they are strong enough to call forth such discrete 

 undulations and succeed in reaching the hair band, are not per- 

 ceived and do not help to make the " timbre " of sounds. 



Should we construct a series of "pure tone" tuning-forks, 

 vibrating from 15 to 40,000 times per second, having a separate 

 fork for each one-eighth of a tone difference, — on setting these 

 forks in vibration one after another, we should find, providing 

 our ears were properly educated, that we experienced a distinct 

 sensation, which we call a simple tone, owing to the constant 

 difference between the periods and intensities of the pendular 

 vibrations thus set up. It will be, for the present at least, 

 allowable to assume that the proportions of the aerial stresses 

 will be maintained in the endolymph, no matter how much the 

 periods and intensities are modified during transmission to the 

 hairs of the nerve end cells. We should thus have a series of 

 tones ranging from i to x. Confining our attention to the coch- 

 lear hair cell rows, we are led to look for the physical cause — 

 the sensation of tone (or sound) — in the periodicity, and not in 

 the wave length, as in the case of light waves. One of Koenig's 

 experiments illustrates this very well. Two simple forks are 



