Note 86 — PREFATORY NOTE.

For Bruno's conjecture (in 1591), see Jevons, vol. ii., p. 299. For Kant's part in the nebular hypothesis, see Lange, Geschichte des Materialismus, vol. i., p. 266. For value of Plateau's beautiful experiment very cautiously estimated, see W. Stanley Jevons, Principles of Science, London, 1874, vol. ii., p. 36. Also, Elisée Réclus, The Earth, translated by Woodward, vol. i., pp. 14-18, for an estimate still more careful. For a general account of discoveries of nature of nebulæ by spectroscope, see Draper, Conflict between Religion and Science. For a careful discussion regarding the spectra of solid, liquid, and gaseous bodies, see Schellen, Spectrum Analysis, pp. 100, et seq. For a very thorough discussion of the bearings of discoveries made by spectrum analysis upon the nebular hypothesis, ibid., pp. 532-537. For a presentation of the difficulties yet unsolved, see article by Plummer, in London Popular Science Review for January, 1875. For excellent short summary of recent observations and thought on this subject, see T. Sterry Hunt, Address at the Priestley Centennial, pp. 7, 8. For an interesting modification of this hypothesis, see Proctor's recent writings.