Acoustical Experiments. 451 



of sound-perception our estimate of pitch depends entirely on 

 localization of the most strongly agitated portion of the basilar 

 membrane, so that in the case just considered, when the note 

 c was made to change from a very small to a very much 

 greater intensity, we should expect to hear not only an in- 

 crease of loudness, but also a lowering of pitch. 



8. At the same time it is not to be supposed that the 

 agitation of the " c-string " is lessened when the intensity of 

 the note c is augmented. The effect must necessarily be in 

 the other direction, so that sach a note powerfully sounded 

 close to the ear must perceptibly excite a tract of the basilar 

 membrane corresponding to a considerable range of pitch (the 

 place of maximum disturbance being probably not far from 

 the middle of this range) . 



9. We must even suppose that an increase in the intensity 

 of a note without change of frequency causes the " range of 

 stimulation " (as we may call it) to extend to patches a little 

 higher than before, as well as to those a good deal lower. 



10. In connexion with § 8 it may be remarked that, when 

 the ear is kept close to the resonant cavity of a strongly- 

 vibrating c-fork, the impression of pitch obtained is far from 

 being very definite. One pitch or another within an appre- 

 ciable range may be heard by a mere effort of attention. On 

 the other hand, a more definite impression is obtained on 

 alternating between smaller and greater intensities of the 

 same note. Thus, on raising or lowering the head, as men- 

 tioned in § 3, the interval between the soft note and the loud 

 note may appear at first to be about a minor third, when the 

 fork is sounding strongly. As the amplitude of vibration dies 

 down, the interval diminishes, and it is possible to say pretty 

 definitely when it is just a whole tone, and when it is only a 

 semitone ; until, as the note in either position of the head 

 becomes nearly inaudible, the apparent difference of pitch is 

 obliterated. 



11. If the orifice of the ear remote from the fork is left 

 open, the sound reaching that ear will be less intense than is 

 heard by the other ear, and the corresponding pitch will be 

 higher. Though of course beats are entirely absent*, it might 

 be thought that two distinct pitches would be heard simulta- 

 neously, but this requires a distinct effort of attention. The 

 general impression is of a pitch intermediate between those 

 which would be heard by the two ears separately, so that on 



* In the discussion Prof. S. P. Thompson suggested that, if the 

 observations were valid, heats should occur between the notes heard 

 by the two ears ; but a consideration of the physical conditions will show 

 that nothing of this kind is to be expected. 



