158 THEORY OF COMPOUND SOUNDS. 



fame reafon, if light be confidered as a vibrating medium; on£ 



particle of the luminous fluid may affift in tranfmitting two 



fenfations. 



The dire&ions Corollary 2. When the inclination of the planes MO, NO, 



will not be pet- j s ] e f s t ^ an a cri ven angle, the ear cannot diftinguifli the rela- 



ceived unJels o o * o 



they differ by a tive pofitions of the founding bodies,- it therefore refers them 

 certain angle. to the fame place. 



The firfl time I perufed Dr. Smith's Harmonics, Dr. Young's 

 objection occurred to me ; but the preceding train of argu*- 

 ments removed the fcruple, without difcovering the author's 

 reafons for treating this article of his work with fo much bre- 

 vity. Perhaps the demonftration, which coft me an effort of 

 fludy, was an intuitive concluiion in his comprehenfive mind. 

 Interval of As foon as the propofition was eftablifhed, I aflented to his 

 found. definition of an interval of found, allowing it to be a quantity 



of a certain kind, terminated by a graver and an acuter found. 

 The demonftration of Prop. V. convinced me, that intervals 

 of this fort may be fubdivided by the interpofition of one or 

 more intermediate founds, which conceflion formed the bafis 

 Analyfisofthe of my analyfis of the human voice.* Speculative men may 

 human vokc. differ in opinion about the origin of the fmall intervals which 

 form the tones of various voices ; but they muft exift, whether 

 we afcribe them to an undulating motion like that of a ftretched 

 cord, or to the cotemporary vibrations of a fyftem of elaftic 

 bodies. It does not appear, that Dr. Young was acquainted 

 with my paper at the time he compofed his own ; but he found 

 it neceflary to allow the tone of the larynx to receive various 

 modifications from the vibrations of the adjacent parts. His 

 theory therefore differs from mine in this particular only : he 

 pronounces the voice to be a compound by coalefcence ; I 

 deny the poffiblility of fuch a compound, and call it a mixture 

 of imperfect unilbns. This mixture appears to be a iingie 

 found, becaufe it has but one direction ; for the proximity of 

 the various parts contributing to the formation of it, difqualifies 

 the ear, fo that it cannot perceive their relative pofitions, and 

 compels it to refer them all to one place, by Corollary 2 to 

 propofition V. 



* Manchefter Mem. v. 58, or Phil. Journal, Quarto, IV. 46*. 

 for an abridged ftatement. 



A certain 



