Ear, power of, to analyze sound, 182, 183 Echelon waves made by a duck, 74 Eddies in liquids, 60 Eddy, 60 —— motion, 60 —— resistance, 68 Edison phonograph, 142 Elasticity of the air, 111 Electric circuit, open, 217 —— conductor and non-conductor, 197 —— corpuscles, 227 —— current, 193 —— ——, alternating, 194 —— ——, continuous, 194 —— —— energy, 215 —— ——, nature of, 193 —— displacement, 221 —— energy, mechanical analogue of, 216 —— force, 228 Electric index of refraction, 245 —— inductance, 214 —— inertia, 214 —— oscillations, 185 —— ——, apparatus for producing, 203 —— —— in open circuit, 217, 218 —— —— produced by discharge of Leyden jar, 200 —— radiation, 238 —— —— and light, identity in nature of, 251 —— radiation-detector (Fleming), 224 —— —— (Miller), 235 —— radiation, velocity of, 249 —— ray, reflection of, 241 —— ——, refraction of, 243 —— strain, 197 —— transparency and opacity, 239, 240 —— wave and air wave compared, 223 —— —— detector, 210 —— ——, nature of, 230 —— ——, production of, 209 —— waves, 185 Electrical or Hertz rays, 254 Electrodeless discharge, 205 —— ——, apparatus for producing, 206 Electro-magnet, 195 Electro-magnetic medium, 220 —— theory of light, 262 Electromotive force, 196 Electronic theory of electricity, 229 Electrons, 227 Energy, 21 ——, kinetic, 25 —— of electro-static strain, 215 —— of motion, 25 —— of moving water, 32 ——, potential, 25 ——, two forms of electric, 215 Ether, the, 191 Experimental tank, uses of, in ship-design, 86 —— tanks, 85, 86 Experiments illustrating surface tension, 40, 41 Explosion of guns heard at great distances, 120 F Falling bodies, laws of, 35 Fish, motion of a, 67 Flame, sensitive, 127 Flow of liquid in non-uniform tubes, 66 —— —— in tubes, 65 —— —— in uniform tubes, 65 Fog-signals, 123 ——, influence of wind upon distance at which they are heard, 124 ——, power absorbed in making, 125 Free period of vibration, influence upon force required to move a body, 151, 152 Froude, Mr. William, 81 Froude’s experimental tank, 81 —— experiments at Torquay, 81 G Gamut, 160 —— of æther waves, 260 Gravitation wave, 40 Ground swell, 31 H Harmonic curve, 108 —— motion, 107 Harmonics, 156 Hele-Shaw, Professor, 62 —— ——, discovery of means of producing irrotational motion in liquids, 63 —— ——, investigations on liquid motion, 63 Helmholtz’s investigation into nature of musical tones, 167 —— theory of discords and concords, 165 Hertz oscillation, 207 Hertz’s researches. Experiments with electric waves, apparatus for, 234 Hughes, Professor, investigations on electric waves, made by, 210 Human ear, the, 181 Hydraulic gradient, 65 I