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
----Wuensch 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 conclusio