Lord Bayleigh : Acoustical Notes. 319 



consecutively. If the right telephone be the first applied, 

 the sensation of course is of a sound to the right. When the 

 left telephone follows, the sound remains on the right and 

 appears louder. If on the other hand the left telephone be 

 the first applied, the sound appearing originally to be on the 

 left transfers itself to the right as the second telephone comes 

 into action. Under the best conditions there seems to be 

 nothing remaining over on the left. 



The results are thus confirmatory of those obtained from 

 tuning-forks. Unquestionably we are able to take account 

 of the phase-difference at the two ears, and this in the case 

 of low pitch is the foundation of the secure judgement as to 

 directiou that we are able to form when a single sound is 

 heard from the right or from the left. With respect to the 

 convenience of the two methods of experimenting, much of 

 course depends upon what appliances are available. In most 

 laboratories, I suppose, the tuning-forks would be preferred. 



Multiple Harmonic Resonator. 



The use of Helmholtz resonators to demonstrate the com- 

 pound character of a musical note is now familiar. The 

 harmonic component tone which has the pitch of the resonator 

 is specially reinforced and so rendered conspicuous even to 

 untrained ears. By changing the resonator, the fundamental 

 tone or any of the harmonics maybe intensified in succession. 



Such effects are rendered far more striking if the 

 necessary changes of pitch can be brought about in a single 

 resonator, which then remains continuously connected with 

 the ear. We may do a little in this direction with a resonator 

 of the usual Konig pattern. Choosing one of somewhat high 

 pitch and listening to a harmonium note two or three octaves 

 down, we find that various harmonics swell out in turn as we 

 pass the finger over the aperture, thereby gradually lowering 

 the pitch to which the resonator responds. 



The idea is carried out more completely if the resonator is 

 provided with a number of separate apertures, any or all of 

 wdiich can be completely closed with the fingers. According 

 to the simple approximate theory * the natural frequency Qs) 

 of the resonator is given by 



X 



W®> w 



where a is the velocity of sound in air, S the volume included 

 in the resonator, and c the electrical conductivity between 

 the interior and exterior calculated upon the supposition that 

 air is a conductor of unit specific conducting power and that 



* Theory of Sound, §§ 304, 305, 306. 



