250 Royal Irish Academy. 



All these principles have received very full verification from an 

 instrument constructed for the purpose, and termed a Chorizophone . 

 It consists of a square glass plate, which is placed above a set of 

 closed tubes of such size, that when the plate vibrates in four pieces, 

 with diagonal nodal lines, the length of each tube is half the length 

 of the phase of the wave produced, and their form is triangular, of 

 the magnitude of one of the four vibrating portions of the plate ; 

 when one of these tubes is presented to the plate, and this brought 

 to vibrate by a violin bow applied to the centre of one of the sides, 

 the tube resounds, and more loudly in proportion as the plate is 

 brought nearer to its orifice. Now here the entire wave from the 

 plate is caught by the tube, and the more perfectly 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 dis- 

 posed as follows : — 



The vibrating plate gives eight waves, four above and four below, 

 4 being -f- and 4 — . 



"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 ab- 

 sorbed, and produces an audible sound. 



With two tubes, the waves absorbed may be either of opposite 

 or of the same phases. If opposite, then the remaining waves are 

 3 + and 3 — , and no sound is produced; but if the waves ab- 

 sorbed 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 + 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 + and 2 — . In the former case, the remaining 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. 



A vibrating plate gives some sound always, even without the 

 tubes, for since there are at least eight waves, some one will always 

 be more favourably disposed for acting on the ear than another : this 

 difference will increase with the number of waves ; and hence the 

 independent sound of a plate increases in proportion as the vibrating 

 portions into which it divides become more numerous. 



