$4 Experimenii and Inquiries rtfpeEiing Sound and Light. 



a fimilar conclufion. The fame inference would follow from a completion of the reafoning 

 of Dr. Helfliam, Dr. Matthew Young, and ProfefTor Venturi. It has been very elegantly 

 demonftrated by Maclaurhi, and may alfo be proved in a much more fimple manner, that 

 when motion is communicated through a feries of elaftic bodies increafing in magnitude, 

 if the number of bodies be fuppofed infinitely great, and their difference infinitely fmall, 

 the motion of the laft will be to that of the firft in the fubduplicate ratio of their refpecSlire 

 magnitudes -y and, flnce in the cafe of concentric fpherical laminae of air, the bulk increafes 

 in the duplicate ratio of the diftance, the motion will in this cafe be dire£tly, and the 

 velocity inverfely, as the diftance. But, however true this may be of the firft impulfe. It 

 will appear, by purfuing the calculation a little further, that every one of the elaftic bodies, 

 except the laft, receives an impulfe In a retrogade dire£lIon, which ultimately impedes the 

 efFeft of the fucceeding impulfe, as much as a fimilar caufe promoted that of the preceding 

 one : and thus, as found muft be conceived to confift of an infinite number of Impulfes, , 

 the motion of the laft lamina will be precifely equal to that of the firft ; and, as far as this 

 mode of reafoning goes, found muft decay in the duplicate ratio of the diftance. Hence 

 it appears, that the propofal for adopting the logarithmic curve for the form of the fpeaking 

 trumpet, was founded on fallacious reafoning. The calculation of M. de la Grange Is left 

 for future examination j and it is intended, in the mean time, to attempt to afcerlain the- 

 decay of found as nearly as poffible by experiment : fliould the refult favour the conclufions 

 from that calculation, it would cftabllih a marked difference between the propagation of. 

 found and of light. 



VIII. Of the harmonic Sounds . of Pipes. 



Ih order to afcertain the velocity with which organ pipes of different lengths require to 

 be fupplied with air, according to the various appropriate founds which they produce, a fet 

 of experiments was made, with the fame mouth-piece, on pipes of the fame bore, and of 

 different lengths, both ftopped and open. The general refult was, that a fimilar blaft pro- 

 duced as nearly the fame found as the length of the pipes would permit ; or at leaft that 

 the exceptions, though very numerous, lay equally on each fide of this conclufion. The 

 particular refults are expreffed In Table xi. and in Plate V. Fig. 28. They explain how a 

 note may be made much louder on a wind Inftrument by a fweli, than it can poffibly be by 

 a fudden Impreflion of the blaft. It is propofed, at a future time, to afcertain by experi- 

 ment, the aftual compreffion of the air within the pipe under different circumftances : 

 from -fome very flight trials, it feemed to be nearly in the ratio of the frequency of vibra- 

 tions of each harmonic. 



Tailt 



