17 



wave from the plate is caught by the tube, and the more per- 

 fectly its escape into the air is prevented, the louder is the 

 sound produced, the sound must arise therefore from the 

 waves which do not pass into the tube. Any one or more 

 waves may thus be absorbed by the closed tubes, and a range 

 of loudness of sound produced from the same plate with one 

 or more of the four tubes, according as they are disposed as 

 follows : 



The vibrating plate gives eight waves, four above and 

 four below, 4 being + and 4 minus. 



With one tube, one wave is absorbed, and 3 -f- and 3 — 

 destroying each other, a wave remains opposite in phase to 

 that which is absorbed, and produces an audible sound. 



With two tubes, the waves absorbed maybe either of op- 

 posite or of the same phases. If opposite, then, the remain- 

 ing waves are 3 -\-and3 — , and no sound is produced; but 

 if the waves absorbed be of the same phase as +) then there 

 remains 4 — and 2 -|-, and hence the ear is doubly affected 

 ,by 2 — . The two tubes may be either both above or both 

 below, or one above and one below the plate. 



With three tubes, the absorbed waves may be either all 

 of the same phase, or two of one and one of the other. In the 

 first instance, 3 + being absorbed, there remains 4 — and 

 1 — , and the ear receives the impulse of 3 — . In the other 

 case 2 -f- and 1 — being absorbed, there remains 2 + and 3 — 

 and the impulse on the ear is only 1 — . The position of the 

 tubes may vary in this as in the former case. 



With four tubes, the absorption may be either all of the 

 same phase, or 2 4- and 2 — . In the former case, the re- 

 maining waves will be either 4 + or 4 — , in which case the 

 greatest sound the plate can produce is heard, or else there 

 remain 2 -{■ and 2 — , in which case the plate gives no sound. 

 These results prove fully that it is the residual sound that is 

 heard, and not that which passes into the tube. 



VOL. II. c 



