406 INDEX 
Persico, E., 280 
Perturbation of electron orbits, 71 
Pettit, E., 206 
Photometric orbits, 148, 209 
Photosphere, 334, 360 
Planck’s constant, 46, 395 
Planck’s law, 21, 49, 53, 55 
Planetary nebulae, 389 
Plaskett, H. H., 330, 342 
Plaskett, J. S., 148, 156, 214, 378 
Plummer, H. C., 185 
Point-source of energy, solution for, 124 
Polytropic gas-sphere, 80; tables, 82; in 
complete, 94; applicable to stars, 117, 128 
Potential, gravitational, 79; at centre of 
star, 83, 85 
Potential energy of polytrope, 86 ; of a star, 
141 
Poynting vector, 57 
Pressure, 79; at centre of a star, 85, 91; in 
reversing layer, 349; in photosphere, 360; 
electrostatic correction to, 266, 269; 
broadening of lines by, 353 
Pressure of radiation, 15; theory of, 27; 
numerical value, 38; ratio to whole pres 
sure, formulae, 117, 129; tables, 117, 137; 
determines stellar masses, 16, 118, 308; 
stress components of, 105, 335; in outer 
layers, 357, 360; in chromosphere, 362; 
escape of atoms by, 368 
Principal lines, 74, 346, 349, 363 
Procyon, 152; companion, 155 
Protons, destruction of, 293 
Pseudo-Cepheids, 181 
Pulsation, of Cepheids, 180; criticisms, 185; 
adiabatic theory of, 186; period of, 192; 
limit to amplitude, 194; maintenance of, 
200; of long period variables, 206 
V Puppis, 147 
Quanta, 41, 46; general conception of, 57 
Quantisation, of hydrogen-like ion, 58; of 
molecules, 352; lack of sharpness, 60, 354 
Quantum numbers, 59, 70, 72 
Quartic equation, fundamental, 117, 129 
Radiation, 27; equilibrium of, 35; tempera 
ture of, 37; Stefan’s law, 38; Wien’s law, 
39; Planck’s law, 55; flow of, 101, 322; 
from accelerated electron, 77, 223; pene 
trating, 317 
Radiation of stars (total), 114; relation to 
opacity, 118; relation to mass and radius, 
134; relation to luminosity, 138. See also 
Luminosity, Absolute magnitude, Mass- 
luminosity relation 
Radiation pressure. See Pressure of radia 
tion 
Radiative equilibrium, 9, 97; equation of, 
101, 107, 322 
Radiative viscosity, 281 
Radio-activity, 294, 315, 344 
Radiometer, 138 
Radius, of Cepheids, 182; of long period 
variable, 208; of sun, 395 
Radius of star, 2; interferometer measures, 
6; method of calculating, 13; method for 
Algol, 210 
Rayleigh scattering, 384, 385 
Reflection effect in eclipsing variables, 210, 
213 
Refractive index, 38, 237 
Relativity, 6, 173 
Reversible processes, 32 
Reversing layer, 342; pressure in, 349, 359 
Rigour of proofs, 102 
Ring nebula, 389 
Ritter, A., 5 
Rosseland, S., 109, 238, 243, 264, 401 
Rosseland’s correction, 112, 247, 356, 398 
Rotating stars, brightness of, 287; currents 
in, 285; von Zeipel’s theorem, 282 
Rotation, of Algol, 210; of planetary nebulae, 
389 
Runaway electrons, 302, 320 
Russell, H. N., 7, 148, 160, 163, 177, 295, 
303, 354 
Rutherford, E., 220 
Saha, M. N., 345, 347 
Sampson, R. A., 9 
Scattering by electrons, 74, 243, 384; co 
efficient of, 76 
Schuster, A., 400 
Schwarzschild, K., 9, 322, 342 
Seares, F. H., 174 
Selection principle, 71, 73, 351 
Series in spectra, 74 
Shajn, G., 160, 311 
Shapley, H„ 8, 146, 181, 310, 342, 384 
Shielding of nuclear field by electrons, 67, 71, 
264 
Shinjo, S., 203 
Silicon, spectra of, 345 
Sirius, companion of, 171 
Size of atoms and ions, 165, 262, 359 
Smart, W. M., 312 
Sodium, fixed lines of, 378, 383 
Sorting demon, 37 
Source of stellar energy, 289; relative dis 
tribution of, 122, 295; point-source, 124 
Space, interstellar, 371 ; temperature in, 371, 
377; density in, 372, 382; ionisation in, 
383; absorption of light in, 383; pene 
trating radiation from, 318 
Specific heats, ratio of, 9, 35; for radia 
tion, 10, 29; for stellar material, 270; in 
Cepheids, 157, 190, 203; limit of stability, 
142 
Spectra, X-ray, 70, 230, 234; optical, 72; 
molecular, 350. See also Absorption. 
Emission, Spectral type 
Spectral energy curve, 324