256 PHYSIOLOGY CHAP. 



The most perfect fusion of tones is undoubtedly that of the 

 harmonic particles from which vocal timbre is derived. In this 

 case, however, the chord has no intrinsic period, but it is blended 

 with that of the vibrations of the fundamental tone, which, by 

 assimilating all the other tones, assumes a specific quality or 

 colour. 



Combinations of tones may therefore lie classified as: 



(a) Chords which give timbre ; this is the maximal degree 

 of fusion. 



(&) Musical chords with an intrinsic period, in which the 

 fusion is not so complete that the component tones cannot be 

 detected. 



(c) Chords with very long periods, which give rise to no 

 continuous or musical sensation. 



X I II. We have said that little is known of the physico- 

 chemical nature of the central processes that determine audi- 

 tory perception. Minute analysis of these processes, however, 

 reveals certain interesting peculiarities which we must briefly 

 consider. 



It has been fully demonstrated that both the recognition of 

 pitch and the intensity of auditory sensations become more and 

 more definite with each vibration. There is therefore a rising or 

 waxing phase in auditory sensations, which conduces to the clear 

 perception of their fundamental characters. We shall find the 

 same in visual sensations. 



Exner made a series of researches on the minimal number of 

 vibrations necessary for the perception of tones, and proved that 

 at least 16-20 vibrations must impress the ear before there can 

 be a distinct recognition of pitch. At the same time he observed 

 that the C of the great octave becomes clearer and more distinct 

 with each successive vibration, and only attains its maximal 

 degree of intensity after 44 vibrations ; the c of the small octave 

 reaches its maximum only after some 48 vibrations. These 

 experiments tend to show that the intensity of tones increases 

 rapidly at first and then more slowly, so that it is difficult to say 

 at what moment it becomes maximal. 



Similar researches were made by Max Meyer to show how 

 the crude sensation of hearing passes gradually into the clear 

 appreciation of pitch. He employed different sirens with 2, 3, 4, 

 and 5 holes to determine the number of impulses required to 

 perceive/' 1 . With only two impulses there is no recognisable 

 tone ; with three the sound begins to acquire a certain strength ; 

 with four the tone can be recognised, though it is still weak and 

 obscure ; with five the pitch is clearly appreciated. Urbantschitsch 

 studied the same phenomena on both the healthy and diseased 

 ear by employing the tones of tuning-forks of different strength. 

 A very weak tone is only fully appreciable to a sound ear after 



