20. Musical pitch in America. Charles R. Cross, Proc. American Academy of Arts and Sciences, 35, 453-467 (1900).
32. Resonators. Helmholtz, Sensations of Tone, pp. 36-49, 372; Vorlesungen, S. 246. Rayleigh, Theory of Sound, II, pp. 170-235.
42. The phonodeik. D.C. Miller, Physical Review, 28, 151 (1909); Proc. British Association for the Advancement of Science, Winnipeg (1909), p. 414; Proc. British Assocation for the Advancement of Science, Dundee (1912), p. 419; Engineering, London, 94, 550 (1912). pp. 36-49, 372; Vorlesungen, S. 246. Rayleigh, Theory of Sound, II, pp. 170-235.
48. Henrici's harmonic analyzer. O. Henrici, Philosophical Magazine, 38, 110 (1894). H. de Morin, Les Appariels d'Intˇgration, Paris (1913), pp. 162, 171. E. M. Horsburgh, Modern Instruments of Calculation, London (1914), p. 223.
50. Harmonic analyzer and synthesizer. Lord Kelvin, Proc. Royal Society, 27, 371 (1878); Kelvin and Tait, Natural Philosophy, Part I, Appendix B', VII, Cambridge, (1896); Kelvin, Popular Lectures, Vol. III, p. 184.
51. Tide-predicting machine. E.G. Fisher, Engineering News, 66, 69-73 (1911). Special Publication No. 32, United States Coast and Geodetic Survey, Washington (1915).
53. Harmonic analzyer. L. W. Chubb, The Electric Journal (Pittsburgh), Feb. 1914, May, 1914.
88. Artificial vowels. Marage, Physiologie de la Voix, Paris, (1911), p. 92.
90. Tuning-fork synthesis of tones. Helmholtz, Sensations of Tones, pp. 123-128, 398-400.