Origin of audible Sounds. 249 



Thus, Mr. Adams showed long since, that when two closed tubes 

 are placed at right angles to each other, they interfere when made 

 to speak to a tuning fork, and for this effect no explanation has 

 hitherto been given. But it is evident that the tubes being at right 

 angles to each other, the waves destroyed are in opposite phases, 

 and those which remain are in opposite phases 

 also, so that the effect is the same as if no 

 tubes were present at all. The same effect 

 may be produced by a single tube, bent so that 

 its apertures may be at right angles to each 

 other ; the — and -f waves, D and C, meeting 

 in the tube, produce neutralization, and the 

 waves A and B, also + and — , which remain, 

 interfere also, and hence no sound results. In 

 an open tube bent into a circle, as in the figure, 

 the two waves destroyed (A C) are of the same 

 phase, and also those which remain (b D), and hence such a tube 

 sounds with nearly double the power 

 of an ordinary open tube. That it 

 is the sound of the waves which do 

 not go into the tube, and not that 

 of the waves in the tube, we hear, 

 may be shown by applying two 

 closed tubes, as in the next figure. 

 When the two — waves are ab- 

 sorbed by the circular open tube, 

 each closed tube absorbs a + wave, 

 and hence, notwithstanding that 

 there is so much vibrating material, 

 no sound is heard. But if the tubes 

 A and B were open, then the vi- 

 brating centres should have been 

 simply transferred to their further 

 extremities, and the tubes would 

 emit sound as the fork had done 

 without them in the preceding 

 figure. 



If the open tube be double the 

 length of a phase, then the neutral- 

 ization occurs as in the figure, the re- 

 sidual waves being B and F, in opposite phases ; but as their cen- 

 tres are separated so 

 far, they interfere 

 only in hyperboloidal 

 planes, which are not 

 detected unless when 

 carefully sought for, 

 but have been noticed 

 to exist by Savart, although he did not suspect their cause. 



