Lecture Iii. the Age of the Stars 85

Pulsating Stars 85

The Cepheid as a ‘Standard Candle’ 90

The Contraction Hypothesis 94

Subatomic Energy 99

Evolution of the Stars 106

Radiation of Mass 113

APPENDIX

Further Remarks on the Companion of Sirius 122

LIST OF ILLUSTRATIONS

FIG.

1. The Sun. Hydrogen Spectroheliogram. (J. Evershed)

2. Solar Vortices. Hydrogen Spectroheliogram. (Mount Wilson Observatory)

3. Tracks of Alpha Particles (helium atoms). (C. T. R. Wilson)

4. Tracks of Beta Particles (electrons). (C. T. R. Wilson)

5. Ionization by X-rays. (C. T. R. Wilson)

6. Ions produced by Collision of a Beta particle. (C. T. R. Wilson)

7. The Mass-luminosity Curve.

8. The Ring Nebula in Lyra. Slitless Spectrogram. (W. H. Wright)

9. Flash Spectrum of Chromosphere showing Head of the Balmer Series. (British Eclipse Expedition, 14 Jan. 1926)

10. Solar Prominence. (British Eclipse Expedition, 29 May 1919)

11. Star Cluster ω Centauri. (Cape Observatory)