Brewster, Sir David, his chief objection to the undulatory theory of light, 47 Brewster, Sir David, his discovery in biaxal crystals, 209 Brougham, Mr. (afterwards Lord), ridicules Dr. T. Young's speculations, 50, 51 Cæsium, discovery of, 193 Calorescence, 174 Clouds, actinic, 152-154 ----polarization of, 155 Colours of thin plates, 64 ----Boyle's observations on, 65, 66 ----Hooke on the colours of thin plates, 67 ----of striated surfaces, 89, 90 Comet of 1680, Newton's estimate of the temperature of, 168 Crookes, Mr., his discovery of thallium, 193 Crystals, action of, upon light, 98 ----built by polar force, 98 ----illustrations of crystallization, 99 ----architecture of, considered as an introduction to their action upon light, 98 ----bearings of crystallization upon optical phenomena, 106 Crystals, rings surrounding the axes of, uniaxal and biaxal, 145 Cuvier on ardour for knowledge, 220 De Tocqueville, writings of, 215, 222, 223 Descartes, his explanation of the rainbow, 24, 25 ----his ideas respecting the transmission of light, 43 ----his notion of light, 207 Diamond, ignition of a, in oxygen, 169 Diathermancy, 173 Diffraction of light, phenomena of, 78 ----bands, 78, 79 ----explanation of, 80 ----colours produced by, 89 Dollond, his experiments on achromatism, 28 Draper, Dr., his investigation on heat, 172 Drummond light, spectrum of, 195 Earth, daily orbit of, 74 Electric beam, heat of the, 168 Electricity, discoveries in, 217, 218 Emission theory of light, bases of the, 45 ----Newton espouses the theory, and the results of this espousal, 77 Ether, Huyghens and Euler advocate and defend the conception of an, 48, 58 ----objected to by Newton, 58 Euler espouses and defends the conception of an ether, 48, 58 Eusebius on the natural philosophers of his time, 13 Expansion by cold, 104 Experiment, uses of, 3 Eye, the, its imperfections, grown for ages towards perfection, 8 ----imperfect achromatism of the, 29, _note_ Faraday, Michael, his discovery of magneto-electricity, 218 'Fits,' theory of, 73 ----its explanation of Newton's rings, 74 ----overthrow of the theory, 77 Fizeau determines the velocity of light, 22 Fluorescence, Stokes's discovery of, 161 ----the name, 174 Forbes, Professor, polarizes and depolarizes heat, 180 Foucault, determines the velocity of light, 22 ----his experiments on absorption, 197, 198 Fraunhofer, his theoretical calculations respecting diffraction, 87 ----his lines, 193 ------their explanation by Kirchhoff, 193 Fresnel, and Dr. Young, 50 ----his theoretical calculations respecting diffraction, 87 ----his mathematical abilities and immortal name, 210 Goethe on fluorescence, 165 Gravitation, origin of the notion of the attraction of, 92 ----strength of the theory of, 148 Grimaldi, his discovery with respect to light, 56 ----Young's generalizations of, 56 Hamilton, Sir William, of Dublin, his discovery of conical refraction, 209