respecting Sound and Light. 1 3 1 



be of the first impulse, it will appear, by pursuing the calcula- 

 tion a little further, that every one of the elastic bodies, except 

 the last, receives an impulse in a retrograde direction, which 

 ultimately impedes the effect of the succeeding impulse, as much 

 as a similar cause promoted that of the preceding one : and 

 thus, as sound must be conceived to consist of an infinite 

 number of impulses, the motion of the last lamina will be pre- 

 cisely equal to that of the first; and, as far as this mode of 

 reasoning goes, sound must decay in the duplicate ratio of the 

 distance. Hence it appears, that the proposal for adopting the 

 logarithmic curve for the form of the speaking trumpet, was 

 founded on fallacious reasoning. The calculation of M. De la 

 Grange is left for future examination ; and it is intended, in the 

 mean time, to attempt to ascertain the decay of sound as nearly 

 as possible by experiment: should the result favour the con- 

 clusions from that calculation, it would establish a marked 

 difference between the propagation of sound and of light. 



VIII. Of the harmonic Sounds of Pipes. 



In order to ascertain the velocity with which organ pipes of 

 different lengths require to be supplied with air, according to 

 the various appropriate sounds which they produce, a set of 

 experiments was made, with the same mouth-piece, on pipes 

 of the same bore, and of different lengths, both stopped and 

 -open. The general result was, that a similar blast produced as 

 nearly the same sound as the length of the pipes would permit; 

 or at least that the exceptions, though very numerous, lay 

 equally on each side of this conclusion. The particular results 

 are expressed in Table xi. and in Plate IV. Fig. 28. They ex- 

 plain how a note may be made much louder on a wind instrument 



mdccc R 



