452 Some Acoustical Experiments. 



closing the further ear a distinct lowering of pitch takes place. 

 For this reason the effects described in § 3 are most marked 

 when the less stimulated ear is kept closed. 



12. I have not yet mentioned an effect noticed by an ob- 

 server in whom hearing with one ear was not normal. With 

 the less sensitive ear the usual effect was reversed; that is, on 

 bringing the ear close to the resonance-cavity of the c-fork, 

 the pitch, instead of falling, appeared to rise by about a semitone. 

 Even taking § 9 into account, this result seems rather ano- 

 malous. 



13. Though variations of pitch accompanying variations of 

 loudness must frequently have been observed, the physiological 

 influences at work do not appear to have been suspected *. 

 And yet these subjective influences must be by no means 

 negligible in the case of wind-instrument players ; and even 

 from players of stringed instruments I think I have heard 

 that it is easier to judge of another player's intonation than 

 to be quite certain about one's own. On the other hand, as 

 regards the tuning of the intervals of consonant chords, it 

 must be remembered that the actual criterion is usually the 

 obliteration of beats, so that on this point the judgment is not 

 disturbed by a small subjective uncertainty in the estimation 

 of pitch. I have also convinced myself that, when harmonic 

 upper partials are present, the sense of tonality is largely 

 dependent upon them ; and harmonics from their higher 

 pitch and generally feebler intensity will suffer less subjective 

 repression of pitch than the fundamental. 



II. Objective Demonstration of Combination- Tones. 



14. When two notes differing in frequency are powerfully 

 sounded in the neighbourhood of one another, secondary tones 

 are produced, of which the most prominent have frequencies 

 respectively equal to the sum and difference of the frequencies 

 of the parent tones. It has been maintained by some writers 

 that these secondary tones are purely subjective, and have no 

 existence external to the ear, and the following experiment 

 was designed to show that in some cases at least the first 

 difference-tone has a real physical existence. If the vibration 

 of the air external to the ear has really a component of the 

 frequency in question, we must suppose this component to 

 have arisen from a failure of the principle of superposition, 

 that is, from the circumstance that as the parent vibrations 



* For example, Lord Rayleigh mentions (' Theory of Sound/ 2nd ed. 

 vol. i. § 67) that " tuning-forks rise a little, though very little, in pitch 

 as the vibration dies away." 



