Pythagoras, 2, 3, 5, 13 Quantum, defined, 126 Quantum theory, 122 ff., 137 ff., 286, 330, 331 Quotations, Arnold, Matthew, 5 Bede, 7 Bruno, Giordano, 3 Cornford, Frances, 11 Cusa, Nicholas of, 3 Galileo, 5 Meredith, George, 283 Newton, Sir Isaac, 197 Sackville-West, Victoria, 7 Shakespeare, 193 Radiation, 114 ff., 137 ff., 254 ff., 307 distribution by wave-length, 253 highly penetrating, 143, 144, 191, 298, 299 mechanical effects of, 120, 137, 290, 306 of sun, 55, 175, 256 pressure of, 120; in a star, 290, 306 visible and invisible, 258, 259 wave-length of, 122, 255, 258 weight of, 120, 122, 136 Radio-activity, 110 ff., 153, 298 Rainbow, 50, 51, 105 Rayleigh, Lord, 94 Redman, H. O., 277, 349 Relativity, theory of, 74 ff., 186, 261, 323, 337 Ring nebula in Lyra, 29, 274 and Plate II (p. 28) Rings of electrons, in atom, 134, 138, 289, 291 ff., 302, 304, 305 Roche, E., 245, 249 Roche’s limit, 246, 250, 251, 252 Rosse, Lord, 30 Rotating masses, of gas, 206, 221 of liquid, 219, 221 Rotating nebulae, 205 Rotating systems of stars, 168, 213 Rotation, of astronomical bodies, 168, 216 of galaxy, 66 ff., 214 of nebulae, 205 of stars, 217 Royds, T., 112 Russell, H. N., 187, 229, 276, 293, 299, 314 Russell diagram, 276, 277, 278, 282, 283, 291, 295, 302, 303, 314, 338 Rutherford, Sir E., 107, 111, 112, 117, 143, 154