ON THll SOURCES AND EFFECTS OF SOUND. 303 



~* ^Such is tjj^d^licacy of the organs of hearing in their perfect state, that 

 we reaHtfy distinguish not only the frequency of the vibrations of a sound, 

 whether constant or variable, and its loudness or softness, but also the 

 quality of tone, depending on the law which governs each separate vibra- 

 tion, and which constitutes the difference between instruments of different 

 kinds, or different instruments of the same kind, or even the same instru- 

 ment differently employed. Thus, we can distinguish very accurately the 

 voices of our friends, even when they whisper, and those modifications of 

 the same voice which constitute the various vowels and semivowels, and 

 whicil with the initial and final noises denominated consonants, compose 

 the words of a language. We judge also, without an error of many degrees, 

 of the exact direction in which the sound approaches us ; but respecting 

 the manner in which the ear is enabled to make this discrimination, we 

 cannot reason upon any satisfactory grounds. 



LECT. XXXII. ADDITIONAL AUTHORITIES. 



Vibrations of 1. Fluids. Euler on the Motion of Air in Pipes, Nov. Com. 

 Petr. xvi. 281. Chladni, Ph. Mag. iv. 275. Delarive on the Sounds from Hydrogen 

 Gas, Jour, de Physique, Iv. 165 ; Nich. Jour. 8vo, iv. 23. Higgins on do. Nich. 

 Jour. 8vo, i. 129. Biot, Mem. d'Arcueil, ii. 99. Leslie, Trans. Camb. Ph. Soc. 

 i. 267. 



2. Cords. Sauveur on the Sounds of Cords, Hist, et Mem. de Paris, 1713, 

 p. 324, H. 68. Jo. Bernoulli, Com. Petr. iii. 13. D. Bernoulli, Com. Petr. iii. 

 62; Hist, et Mem. de Berlin, 1753, pp. 147, 173. Bernoulli on the Vibrations of 

 Unequal and Compound Cords, Hist, et Mem. de Berlin, 1765, p. 281 ; Nov. Com. 

 Petr. xvi. 257. Euler on the Vibrations of Cords, Hist, et Mem. de Berlin, 1748, 

 p. 69, &c. &c. D'Alembert, ibid. 1747, pp. 214, 220 ; 1750, p. 355 ; 1763, p. 235. 

 Voigton the Nodes of Cords, Ph. Mag. iv. 347. Pellisov, Poggendorf's Annalen, 

 xix. 237. 



3. Surfaces. Biot, Mem. de 1'Institut, iv. 21. Jo. Bernoulli on the Vibrations 

 of Rectangular Plates, Nov. Act. Petr. 1787, v. 197. Voigt, Ph. Mag. iii. 389. 

 Comparisons with Chladni's Experiments. Savart, Annales de Chimie, vol. xii. 

 &c. &c. Kastner's Archiv, B. 8. Faraday, Ph. Tr. 1831, p. 237. Wheatstone, 

 ibid. 1833, p. 593. Tomlinson, Records of General Science, vol. ii. 



Vibrations in general. On Numbering the Vibrations of Sound, Com. Bon. i. 

 180. Poisson sur la Theorie du Son, Journal de 1'Ecole Poly technique, torn. xiv. ; 

 sur le Mouvement dans les Tuyaux Cylindriques, Mem. de 1'Acad. 1818-19, Me- 

 canique, ii. 693. Savart, Annales de Chimie, xliv. 337, xlvii. 69. Cagniard Latour, 

 Annales de Chimie, Ivi. 280. Blein sur la Theorie des Vibrations, 4to, 1827, 8vo, 

 1831. Trevelyan on the Vibrations of Heated Metals, Ph. Mag. 1832, vi. 141, 

 1833. Faraday, Jour, of the Royal Inst. vol. iv. Forbes, Ph. Mag. vol. iv. Trans- 

 actions of the Royal Soc. of Edin. vol. xii. Eisenlohr Lehrbuch der Physik, Mann- 

 heim, 1836. Dove's Repertorium der Physik, Band. vi. 1842. On Reflection of 

 Waves, Annales de Chimie, Ixxi. 20. Fechner, Repertorium der Physik, Band i. 



Interference of Vibrations. Dr. Young pointed out the fact, that a tuning fork 

 held vertically at a short distance from the ear, and turned on its axis, emits a louder 

 or softer sound, according to its position the vibrations of the two prongs tending 

 alternately to strengthen and to diminish each other's effect. Mr. Hopkins (Trans. 

 Camb. Ph. Soc. v. 231) exhibited a similar interference to the eye. 



Ear and Hearing. Perrault on the Organ of Hearing, Hist, et Mem. de Paris, i. 

 158. Duverney, ibid. i. 256. Treatise on do. Lond. 1737. Valsalvade Aure, 4to, 

 Bologna, 1704. Mairan on the Effect of Sound on the Ear, Hist, et Mem. de Paris, 

 1?37, p. 49, H. 97. Nollet on the Hearing of Fishes, Hist, et Mem. de Paris, 1743. 

 Klein on do. Ph. Tr. 1748, p. 233. Arderon on do. ibid. 1748, p. 149. Camper 

 on do. Mem. des Savans Etrangers, vi. 177. Hunter on do. Ph. Tr. 1782, p. 379. 

 Geoffroy on the Hearing of Reptiles, Mem. des Savans Etrangers, ii. 164. Haller, 



