—— sonorous ripples in water, 193 —— Faraday’s and Melde’s experiments on sonorous ripples, 194-195 —— longitudinal vibrations of a wire, 200 —— relative velocities of sound in brass and iron, 203, 206 —— examination of vibrating bars by polarized light, 209 —— determination of velocity in solids, 211 —— relation of velocity to pitch, 212 —— resonance, 213, 253, 256 —— —— of the air, 213, 256 —— —— of coal-gas, 216, 256 —— description of vowel-sounds, 240 —— Kundt’s experiments on sound-figures within tubes, 244-251, 259 —— new methods of determining velocity of sound, 247-251, 259 —— causes that obstruct the propagation of, 306 —— action of fog upon sound, 307 —— contradictory results of fog-signalling, 317 —— solution of contradictions of fog-signalling, 317-318 —— extraordinary case of acoustic opacity, 318 —— great change of acoustic transparency, 323 —— noise of battle unheard, 324 —— echoes from invisible acoustic clouds, 325, 375 —— report of Arago on the velocity of, 328 —— aërial echoes of, 330 —— demonstration of reflection from gases, 332 —— reflection from vapors, 336 —— —— heated air, 337 —— echo from flame, 340 —— investigations of the transmission of sound through the atmosphere, 341 —— action of hail and rain, 341 —— action of snow, 344 —— passage through tissues, 345 —— —— artificial showers, 346 —— action of fog, 347 —— fluctuations of bells, 351-354 —— action of wind, 361 —— atmospheric selection, 365 —— law of vibratory motions in water and air, 377, 407 —— superposition of vibrations, 381 —— interference and coincidence of sonorous waves, 382-383, 407 —— extinction of sound by sound, 384, 407 —— theory of beats, 385, 408 —— action of beats on flame, 387 —— optical illustration of beats, 390, 408 —— various illustrations of beats, 397 —— resultant tones, 399, 409 —— —— conditions of their production, 400 —— —— experimental illustrations, 401 —— —— theories of Young and Helmholtz, 405-406 —— difference-tones and summation-tones, 405 —— combination of musical sounds, 410 —— sympathetic vibrations, 421 —— mode in which sonorous motion is communicated to the auditory nerve, 426 Sound-boards, influence of, 123-124 Sound-figures within tubes, M. Kundt’s experiments with, 244-251 Stars, Doppler’s theory of the colored, 113 Steam-siren, description of, 309 —— conclusive opinion as to its power for a fog-signal, 370 Stethoscope, Dr. Hook’s anticipations of the, 74 Stokes, Professor, his explanation of the action of sound-boards, 124 —— his explanation of the effect of wind on sound, 363 Straw-fiddle, formation of the, 175, 197