Actinic rays, 254 Æther, the, 191 ——, properties of, 192 —— wave radiation, range of, 262 —— waves, various kinds of, 234 Air, movement of, in a concert-room, 183 —— necessary for production of sound, 103 —— particles, mode of motion of, in case of sound wave, 112 —— waves, 103 —— ——, interference of, 139 —— ——, length of, 114 —— ——, nature of, 114 —— ——, speed of, 115 Alphabet used in telegraphy, 274 America Cup race, pictures of yachts entered for the, 94, 95 _America_ yacht, the, 93 Amplitude, 8 Anti-node, 159 Apparatus for detecting electric waves, 237 —— for exhibiting motion of air in case of sound wave, 109 —— for investigating the laws of falling bodies, 35 Atlantic waves, height of, 8 —— ——, length of, 9 Atomic theory, 226 B Beam of sound focused by collodion lens, 131 Beats, Helmholtz’s theory of, 165 ——, musical, 163 Billows, 1 Bore, 38 Branly, Professor, electric wave detector, 211 Breaking wave, 29 C Canal-boat waves, 100 Canal wave, 32 —— —— velocity, 34 Capillary ripples, 44 Chromatic scale, 162 Clef, musical, 160 Closed organ-pipe, 171 Cloud waves, 30 Coherer, Lodge, 212 ——, Marconi, 276 Column of air set in vibration by tuning-fork, 158 Conclusion, 285 Concords and discords in music, nature of difference between, 162 ——, musical, 162 Conditions necessary for production of true wave in a medium, 15 Conductor, electric, 197 Conservation of energy, law of, 23 Conservation of matter, law of, 22 Convergence of an electric ray by a paraffin lens, 243 Cornish, Dr. Vaughan, 31 Corresponding speeds, Froude’s law of, 81 Cup Races, 93 Current, electric, 193 D Dark heat, 250 Deep-sea waves, rule for determining speed of, 11 —— ——, velocity of, 11 Definition of a ripple, 42 —— of wave-frequency, 8 —— of wave-length, 7 Depth of water, effect of, on speed of canal wave, 34 Difference between electric conductors and non-conductors, 198 —— between velocity of a wave and of a wave-train, 20 Discords in music, 162 Dispersion of æther waves, 256 Distances at which sound can be heard, 120 E