Lloyd, Dr., on polarization of heat, 180, 209 Lockyer, Mr., on the rose-coloured solar prominences, 205 Lycopodium, diffraction effects caused by the spores of, 88 Magnetization of light, 141 Malus, his discovery respecting reflected light through Iceland spar, 115 ----discovers the polarization of light by reflection, 208 Masson, his essay on the bands of the induction spark, 202 Melloni, on the polarization of heat, 180 Metals, combustion of, 5, 6 ----spectrum analysis of, 190 ----spectrum bands proved by Bunsen and Kirchhoff to be characteristic of the vapour of, 192 Mill, John Stuart, his scepticism regarding the undulatory theory, 149 Miller, Dr., his drawings and descriptions of the spectra of various coloured flames, 201 Morton, Professor, his discovery of thallene, 162 Mother-of-pearl, colours of, 90 Nature, a savage's interpretation of, 4 Newton, Sir Isaac, his experiments on the composition of solar light, 26 ----his spectrum, 27 ----dispersion, 27 ----arrives at the emission theory of light, 45 ----his objection to the conception of an ether espoused and defended by Huyghens and Euler, 58 ----his optical career, 70 ----his rings, 69-77 ----his rings explained by the theory of 'fits,' 73 ----espouses the emission theory, 77 ----effects of this espousal, 77 ----his idea of gravitation, 92 ----his errors, 208 Nicol prism, the, 122 Ocean, colour of the, 35 OErsted, discovers the deflection of a magnetic needle by an electric current, 176 Optics, science of, 4 Pasteur referred to, 219 Physical theories, origin of, 41-44 Pigments, analysis of the action of, upon light, 33 ----mixture of, contrasted with mixture of lights, 37 ----Helmholtz reveals the cause of the green in the case of mixed blue and yellow pigments, 37 ----impurity of natural colours, 37 Pitch of sound, 59 Plücker, his drawings of spectra, 202 Polariscope, stained glass in the, 130,131 ----unannealed glass in the, 136 Polarity, notion of, how generated, 93 ----atomic, 93-96 ----structural arrangements due to, 96 ----polarization of light, 112 ----tested by tourmaline, 116 ----and by reflection and refraction, 119 ----depolarization, 120 Polarization of light, 112 ----circular, 140 ----sky-light, 149, 157 ----of artificial sky, 156 ----of radiant heat, 180 Polarizer and analyzer, 127 Poles of a magnet, 93 Powell, Professor, on polarization of heat, 180 Prism, the Nicol, 122 Quartz, chromatic phenomena produced by, 139 Radiant heat, 172 ----diathermancy, or perviousness to radiant heat, 173 ----conversion of heat-rays into light rays, 174 ----formation of invisible heat-images, 179 ----polarization of, 180 ----double refraction, 182 ----magnetization of, 184 Rainbow, Descartes' explanation of the, 24 Refraction, demonstration of, 14 Refraction of light, 106 ----double, 109 Reflection, partial and total, 16-20 Respighi, results obtained by, 205 Ritter, his discovery of the ultraviolet rays of the sun, 159