603 



LETTER RESPECTING SOUND AND LIGHT. 



B. Because all refractions are attended with 

 A partial reflection. 



C. Because there is no reason to expect 

 that such a vibration should diverge equally 

 in all directions, and because it is probable 

 that it does diverge in a small degree in every 

 direction. 



I). Because the dispersion of differently 

 coloured rays is no more incompatible with 

 this system than with the common opinion, 

 which only assigns for it the nominal cause 

 -of different elective attractions. 



E. Because refraction and reflection in 

 general are equally explicable on both sup- 

 .positions. 



F. Because inflection is as well, and, it 

 may be added, even much better explained 

 by this theory. 



G. Because all the phenomena of the co- 

 lour* of thin plates, which are in realitj' to- 

 tally unintelligible on the common hypothe- 

 sis, admit a very complete and simple ex- 

 planation by this supposition. The analogy, 

 which is here superficiall}' indicated, will pro- 

 bably soon be made public more in detail ; 

 and will also be extended to the colours of 

 thick plates, and to the fringes produced by 

 inflection, affording, from' Newton's own 

 elaborate experiments, a most convincing ar- 

 gument in favour of this system. 



9. The particles of air may be jointly ac- 

 tuated by two or more sounds; and in this 

 case, the several motions are to be added or 

 subtracted, in order to find the actual joint 

 motion, Sect. XI. 



10. The grave harmonic produced by a 

 major third is accompanied by a very audi- 

 ble twelfth. This circumstance is explained, 

 and the effect of subordinate notes and sub- 

 iiltern stops, on the quality of sounds, is 

 shown by figures. Sect. XI. 



11. A noise returning every second, if 

 audible, would be a C. From Sauveur ; with 

 an experiment. Sect. XII. 



12. A chord retains always the form of its 

 initial, vibration. From experiments, in fa- 

 vour of Euler's theorem, against the simple 

 harmonic curve. Sect. XIII. 



l;]. The vibration of a chord is scarcely 

 ever performed in the same plane. Its revo- 

 lutions, and its subordinate vibrations, may 

 be rendered distinctly visible under the mi- 

 croscope, Sect. XII J. 



14. If a chord be inflected at any point of 

 aliquot division, the harmonic secondary 

 note corresponding to that division will not 

 be audible ; an experiment contradictory to 

 some theories of the origin andof the insepa- 

 rable nature of harmonic sounds, Sect. XIII. 



15. The human voice is analogous to the 

 organ pipe denominated from it, which con- 

 sists of a tongue piece without any commen- 

 surate tube : and the falsetto is probably 

 formed by the upper orifice of the trachea, as- 

 suming the functions of the glottis. Sect. XV. 



16. A temperament of progressive imper- 

 fection is the most convenient for practical 

 music, and is easily approximated by tuning 

 six perfect, and six equally imperfect fifths. 

 Sect. XVT. 



From the detached nature of the subjects 

 which I have here enumerated, and live im- 

 perfect state of those branches of the mathe- 

 matics to which they refer, it would have 

 been in vain to attempt a very perspicuous 

 and detailed discussion of them. My re- 

 searches on these subjects have been much 

 interrupted, and probably will not be very 

 shortly resumed ; but, if they be of no fur- 

 ther use to any person, I shall not think ray 

 labour lost ; for I flaj^ter myself that the in- 

 ferences, which they have led me to draw, re- 



