Angular momentum, atomicity of, 216 Aristotelian philosophy, 9 Atom, 26; the Bohr, 209; constituents of, 41, 189; in helium, 141; hydrogen, 26, 27, 42, 215; impenetrable portion, 194; loose structure of, 139, 194; miniature stellar system, 141; multiply charged 143; nucleus of, 193; size of, 183; structure of, 182; a system, 184 Atom-ion theory, 37 Atomic numbers of elements, 286 Atomic structures, 222, 224, 229, 230, 231; and spectral lines, 205 Atomic system, 193 Atomic theories: of matter, 6, 7, 8, 10, 15, 77, 157; of electricity, 15, 23 f., 66, 163; and strain theory, 18 Atomic weight, 196, 202, 206, 207 Atoms, number of, 195 Avogadro’s constant, 30, 261; rule, 183 Balance, electrical 103; quartz, 103 Balanced-drop method, 57 ff., 66 Balmer-Ritz equation, 210, 215 216 Balmer series, 204, 213, 214 f.; constant of, 214 Black-body radiation, 232, 236, 237 Bohr atom, 209, 211 ff.; orbits for hydrogen, 215; theory, 210, 214, 230, 231; quantum principle, 218 Bohr-Sommerfeld model of hydrogen atom, 219 Bohr’s: derivation of Rydberg constant, 282; periodic table, 226 Brownian movements, 10, 131, 136, 145 ff., 147, 164, 167, 170, 171, 175, 268, 270; determining from, 167; Einstein-, equation, 151, 156, 175, 180; equation, 268; experiments with dust-free air, 165; fluctuations of, 171; in gases, 145, 149, 150, in liquids, 156 Cathode rays, 23 f.; charge on, 80; for, 42; frequencies of X-ray spectra, 197 f. Cavendish Laboratory, 33, 35, 44, 48, 54 Charge: of alpha particle, 158 f.; change of, in drop, 77, 133, 249; constant molecular, 19; electrical, 22, 28, 30, 40, 46; free positive, on atoms, 196; frictional, 72, 73, 76; granular structure of, 77; ionic, 47, 76; mass of, on sphere of radius , 272; multiple, 143; positive and negative, 12, 27; ratio of, to mass, 42; single, 134, value of, 59 Cluster-ion theory, 37 Compton effect, 256, 257 f., 259, 260, 261 (Fig. 36); theory of scattering, 284 ff. [Pg 291] Corpuscular theory, 233 Coulomb, 28 Democritus, principles of, 9 Discontinuity, of radiation, 244, 254 Drop: density of, 114; law of motion of, 124; rigid, 87; velocity of, 86; weighing the, 102 Duane’s effect, 246 : constant value of, 169, 177; essential elements of measurement, 124; exact evaluation of, 90, 103, 114 f.; final value of, 120, 26; fundamental physical and chemical constant, 17; H. A. Wilson’s work on, 54; method of obtaining, 138, 160, 162 f.; Sir J. J. Thomson’s work on, 49, 33; Townsend’s work on, 43 ff., 263; variation in, 169, 171, 172 Einstein-Bohr equation, 248 Einstein’s equation, 146 f., 149, 156; 157, 238, 239, 242, 243, 247, 230; history of, 244 ff. Einstein’s quantum theory, 237, 236 Electricity: absolute unit of, 29, 31; atomic theory of, 6, 10, 21,