238 



INDEX. 



Page. 



Stokes, his discoveries in the spectnim 127 



Sulphate of lime, effect of heat upon 141 



Surface of elasticity 217-18 



equation of 217 



cii'cular sections in , 221 



for crystals of one axis ' 230 



Surface, wave, in double refraction, illustrated 225 



equation of 225 



principal sections of 226 



inosculating points of 225-30 



in crystals of one axis 230 



Surfaces, ruled, appear colored by reflectedlight 183 



Tartrates, rotatory power of 142 



Tension imparts polarizing power 140 



Theories of light 143 



Theory of emission 143 



of undulation 143, 146 



of dispersion, by Cauchy 155-56 



of reflection and refraction, by Huyghens 159 



of double refraction, by Huyghens 160-61 



of polarization in reflection and retraction 188 



Thick plates, colors produced by 120 



Thicknesses which produce color in crystalline plates under polarized light 133 



in Newton's rings 119 



Thin plates, colors produced by 118-20, 183-^7 



Time, measure of, in vibration 149 



Topa!5, elliptic rings seen in 139 



Torsion imparts polarizing power 140 



Total reflection, defined- 138 



limiting angle in 138 



does not polarize common light i;58 



Tourmaline, its peculiar properties 132 



Trajectories in diffraction interferences 174, 176 



Transparency of glass piles •. ni 



Transverse vibrations, basis of the theory of ijolarizatioa -163 



Tremor, definition of 152 



velocity of 152 



how related to undula'ion 152 



Two-axed crystals, optic axes of 139, 227 



Undulatory theory of light 143, 146 



Undulation - 147 



how related to vibration 151-53 



curves - 153, 166 



curves, tlioir nodal points 198 



Undulations unequal for different colors 171 



absolute lengths of 170 



table of 171 



numbers of, per second 171 



of light and sound compared 171 



interfering 162-64, 1G6 



direction of vibrations in 162, 215 



resultant of, in same plane 166 



resultant of, in normal planes 168 



liquid 162-63 



sonorous 15! 



in plane polarization 215 



in circular polarization 197 



in elliptic polarization 198 



Unequal velocities of rays of different colors. . ., 171 



of rays in double refraction 220 



Union of two rays producing darkness 114 



Varieties of molecular movements 157 



Varying elasticity of ether in double refracting crystals 162, 216 



causes of 230 



Velocity of light 121,125 



of sound 153-55 



of sonorous undulations, tmiform 155 



of rays of ditferent colors, unequal 1 55 



of rays in double refraction, unequal 220 



of tremors in elastic fluids 152 



of molecular movements in waves 157 



Vibration 147-51 



Vibration, how converted into revolution 148 



, how related to imdulation - 151-53 



measure of time in 149 



of velocity in 147 



Vibrations, how compounded 148-51 



transverse, tlie h;usis of Pi-esnel's theory 162, 215 



relative, of tlie rays produced by double refraction 162, 220 



of common liglit indeterminate in azimuth 165 



of the pendulum 148 



isochrouism of 147 



Wave surface, illustrated 225 



equation of 225 



■ principal sections of 226 



of crystals of one axis 230 



Wave-progress and ray-progress distinguished 224 



