Light familiar to the ancients, 5 ----generation of, 6, 7 ----spherical aberration of, 8 ----the rectilineal propagation of, and mode of producing it, 9 ----illustration showing that the angle of incidence is equal to the angle of reflection, 10, 11 ----sterility of the Middle Ages, 13 ----history of refraction, 14 ----demonstration of the fact of refraction, 14 ----partial and total reflection of, 16-20 ----velocity of, 20 ----Bradley's discovery of the aberration of light, 21, 22 ----principle of least time, 23 ----Descartes and the rainbow, 24 ----Newton's analysis of, 26, 27 ----synthesis of white light, 30 ----complementary colours, 31 ----yellow and blue lights produce white by their mixture, 31 ----what is the meaning of blackness? 32 ----analysis of the action of pigments upon, 33 ----absorption, 34 ----mixture of pigments contrasted with mixture of lights, 37 ----Wünsch on three simple colours in white light, 39 _note_ ----Newton arrives at the emission theory, 45 ----Young's discovery of the undulatory theory, 49 ----illustrations of wave-motion, 58 ----interference of sound-waves, 58 ----velocity of, 60 ----principle of interference of waves of, 61 ----phenomena which first suggested the undulatory theory 62-69 ----soap-bubbles and their colours, 62-65 ----Newton's rings, 69-77 ----his espousal of the emission theory, and the results of this espousal, 77 ----transmitted light, 77 ----diffraction, 77, 89 ----origin of the notion of the attraction of gravitation, 92 ----polarity, how generated, 93 ----action of crystals upon, 98 ----refraction of, 106 ----elasticity and density, 108 ----double refraction, 109 ----chromatic phenomena produced by crystals in polarized, 121 ----the Nicol prism, 122 ----mechanism of, 125 ----vibrations, 125 ----composition and resolution of vibrations, 128 ----polarizer and analyzer, 127 ----recompounding the two systems of waves by the analyzer, 129 ----interference thus rendered possible, 131 ----chromatic phenomena produced by quartz, 139 ----magnetization, of, 141 ----rings surrounding the axes of crystals, 143 ----colour and polarization of sky, 149, 154 ----range of vision incommensurate with range of radiation, 159 ----effect of thallene on the spectrum, 162 ----fluorescence, 162 ----transparency, 167 ----the ultra-red rays, 170 ----part played in Nature by these rays, 175 ----conversion of heat-rays into light-rays, 176 ----identity of radiant heat and, 177 ----polarization of heat, 180 ----principles of spectrum analysis, 189 ----spectra of incandescent vapours, 190 ----Fraunhofer's lines, and Kirchhoff's explanation of them, 193 ----solar chemistry, 195-197 ----demonstration of analogy between sound and, 198, 199 ----Kirchhoff and his precursors, 201 ----rose-coloured solar prominences, 204 ----results obtained by various workers, 205 ----summary and conclusion, 206 ----polarized, the spectra of, 227 ----measurement of the waves of, 234 Lignum Nephriticum, fluorescence of, 164