



Lord Kayleigh : Acoustical JVotes. 327 



excited by bowing it emitted a very powerful sound 

 and, largely in consequence, came somewhat rapidly to 

 rest. The isolation of the vibrations was thus far from 

 complete. 



The principal loads, of 10 gms. each, were in the form 

 of nuts and travelled along screws passing through the 

 prongs near their ends and parallel to the direction of vibra- 

 tion. Suitable lock-nuts kept all tight. In consequence of 

 the loading, the pitch fell about a major third, and the tuning 

 of the resonance-box had to be readjusted by a piece of board 

 obstructing the mouth. It soon appeared that, as had been 

 expected, when the loads were outside the prongs the sound 

 diminished as they were moved inwards as far as possible. 

 To obtain a minimum, the loads must be inside the prongs : 

 and a great falling off was readily achieved by adjustment of 

 their position. 



At this stage considerable difficulty was experienced in 

 appreciating the quality of the residual sound, but it was 

 suspected that most of it was octave, in spite of the fact that 

 the resonance-box was tuned to the fundamental tone. The 

 device appropriate to stop tones of a particular pitch from 

 gaining access to the ear is a Quincke tube. A straight 

 length of composition metal tubing, open at both ends, was 

 provided with a lateral connexion at a distance from the 

 outer end amounting to ^ A, of the octave tone. The whole 

 length was nearly the double of this, and the other end was 

 inserted in the resonance-box. At the same time the ear was 

 connected with the lateral branch with the aid of an india- 

 rubber prolongation. AVhen the outer end of the straight 

 tube is closed with the thumb, that end becomes a node of 

 the stationary vibrations of octave pitch executed therein, 

 and as the junction with the lateral tube is distant |- X from 

 the end that place is a loop, and consequently no (octave) 

 vibration is propagated to the ear. The application of the 

 thumb accordingly has the effect of freeing the possibly com- 

 pound sound from its octave component, while it leaves the 

 fundamental tone in full vigour. 



The application of this test proved at once that by far the 

 greater part of the residual sound heard when the loads were 

 in approximate adjustment was in fact octave. Immediately 

 after bowing, when the vibrations of the fork are vigorous, 

 a loud sound is heard when the outer end of the Quincke 

 tube is open, but comparative silence ensues when the thumb 

 is applied. As the vibration dies down, closing the end has 

 less effect. 



In this way it appeared that in reality a great measure of 



