De Sitter, 21
Displacement of spectral lines, 124, 155
Distance (line-interval), 3, 5, 8, 34, 35, 99, 104, 129
——— physical interpretation of, 5
——— relativity of, 34
Doppler principle, 59
Double stars, 21
Eclipse of star, 21
Eddington, 124, 154
Electricity, 90
Electrodynamics, 15, 24, 48, 52, 90
Electromagnetic theory, 58
——— waves, 75
Electron, 52, 60
——— electrical masses of, 60
Electrostatics, 90
Elliptical space, 133
Empirical laws, 148
Encounter (space-time coincidence), 113
Equivalent, 16
Euclidean geometry, 1, 2, 68, 97, 101, 104, 128, 120, 135, 147
—————— propositions of, 3, 8
——— space 68, 102, 147
Evershed, 158
Experience, 59, 70
Faraday, 56, 74
FitzGerald, 63
Fixed stars, 12
Fizeau, 46, 58, 61
——— experiment of, 46
Frequency of atom, 157
Gallilei, 12
——— transformation, 40, 43, 45, 50, 61
Galileian system of co-ordinates, 13, 15, 17, 54, 93, 108, 116, 119
Gauss, 102, 103, 106
Gaussian co-ordinates, 103, 105, 112, 114–118
General theory of relativity, 69–124, 115
Geometrical ideas, 2, 3
——— propositions, 1
—————— truth of, 2–4
Gravitation, 75, 82, 92, 121
Gravitational field, 75, 79, 87, 91, 111, 116, 119, 120, 136
—————— potential of, 157
——— mass, 76, 81, 121
Grebe, 158
Group-density of stars, 126
Helmholtz, 128
Heuristic value of relativity, 50
Induction, 148, 149
Inertia, 77
Inertial mass, 55, 76, 81, 120, 121
Instantaneous photograph (snapshot), 141
Intensity of gravitational field, 127
