v TIIK SKNSK ol IIKAUINtJ 



tlio membrane of the fenestra rotunda, or by tin; resistance \' tin- 

 basilar membrane; on tbe other hand, the \vaves ascending along 

 the scala vestibuli can easily be transmitted by the thin, loose 

 membrane of Reissner to the endolymph, tectorial membrane, 

 filaments of the hair-cells and terminations of the cochlear nerve. 

 There is accordingly no need to assume any intervention of the 

 supposed vibratory movements of the basilar membrane in order 

 to explain the physiological process of excitation of the auditory 

 nerve by means of the adequate stimulus of the sound-waves. 

 The vibrations of the membrana tectoria suffice. 



We still have to solve the far more difficult problem of how 

 the peripheral organ of hearing is capable of arousing auditory 

 impressions with all their distinctive qualitative characters in 

 consciousness. Before attacking this problem, to the solution 

 of which all theories of audition are directed, the physical qualities 

 of sound-waves, and our faculty of perceiving them as such, must 

 be briefly discussed. 



VII. A primary distinction in auditory sensations, which has 

 been generally admitted since Helmholtx, is that of sot/m/* and 

 noises. Although this distinction is sanctioned by common 

 parlance, it is not easy to give an exact psycho-physiological 

 definition of these two terms. 



Speaking generally, sounds (or tones in a wider sense) are the 

 auditory sensations which run an equal, balanced, regular course ; 

 noises are auditory sensations which, when they have a certain 

 duration and are not merely a single impact or sudden shock, are 

 distinguished by harshness and instability, and are not uniform. 

 The acoustic impressions produced by musical instruments are 

 the best examples of sensations of tone ; whispering, whistling, 

 the howling of wind, the splashing of rain, the cracking of 

 thunder, the rattling of a cart, the rasping of a saw, are examples 

 of different kinds of noises. Yet though tones are quite distinct 

 from noises in their extreme forms, these distinctive characteristics 

 are modified in the intermediate forms, and may gradually merge 

 into one another, or the former may mix with the latter in 

 varying relations. Musical tones, also, may create a noise, as 

 when all the keys of a piano are struck together for the range of 

 one or two octaves. 



Differences of duration, intensity, uniformity, and above all 

 pitch can be detected, not only in tones, but also in noises. 

 The tones associated with noises are termed harsh, raucous, 

 strident, etc. It may safely be aflirmed that both tones and 

 noises are compound auditory sensations, resulting from the 

 mixture of a certain number of elements, known as simple tones. 



On investigating the nature of the stimuli that arouse auditory 

 sensations in the ear they appear to tin- tactile sense to be 

 quivering, to the eye to be vibrating bodies with blurred outlines. 



