224 Lord Bayleigh on our 



character o£ pure tones. Although the cycle could be 

 recognized, a distinct lateral effect was not perceived, and the 

 failure was evidently connected with the composite character 

 of the sounds. By loading the disks of the telephones with 

 penny-pieces (attached at the centres with wax) the higher 

 components could be better eliminated. It was then possible to 

 fix the attention upon the fundamental tone and to recognize 

 its transference from left to right during the cycle. But the 

 effect was by no means so conspicuous as with the tubes, and 

 might perhaps be missed by an unprepared observer *. 



The subject now under consideration is illustrated by a 

 curious observation accidentally made in the course o£ another 

 inquiry. A large tuning-fork of frequency about 100, 

 mounted upon a resonance-box, was under examination with a 

 Quincke tube. This consisted of a piece of lead pipe more 

 than one quarter of a wave-length long, one end o£ which was 

 inserted into the resonance-box. At a distance o£ one eighth 

 o£ a wave-length from the outer end a lateral tube was 

 attached which communicated with one ear by means of an 

 india-rubber prolongation. When the second ear was closed, 

 it appeared to make no difference to the sound whether or not 

 the outer end of the Quincke tube was closed with the thumb. 

 But when the second ear was open, marked changes in the 

 sound accompanied the opening and closing of the Quincke 

 tube. On the view hitherto held, it would appear very para- 

 doxical that a change not affecting the sound heard in either 

 ear separately should be able to manifest itself so conspicuously. 

 It was easily recognized that the alterations observed were 

 o£ the nature of right and left effects, and that they could be 

 explained by the local reversal of phase which accompanied 

 the closing of the Quincke tube. 



The conclusion, no longer to be resisted, that when a sound 

 of low pitch reaches the two ears with approximately equal 

 intensities but with a phase-difference of one quarter of a 

 period, we are able so easily to distinguish at which ear the 

 phase is in advance, must have far reaching consequences in 

 the theory of audition. It seems no longer possible to hold 

 that the vibratory character of sound terminates at the outer 



* Subsequently by a muck heavier loading (53 gms.) the telephone-plates 

 were tuned approximately to pitch 128, as could be verified by tapping 

 them with the finger. To find room for these extra loads, the ear-pieces 

 of the telephones had to be modified. The sounds now heard were very 

 approximately pure tones, and the lateral effects were as distinct as those 

 observed when the sounds were conveyed through tubes. It is easy to 

 understand that considerable complication must attend an accompaniment 

 of octave and higher harmonics, which would transfer themselves from 

 right to left more rapidly than the fundamental tone. 



