Chapter III: Part II

PROBLEMS IN SIDEREAL PHYSICS
1. PROGRESS OF SIDEREAL PHYSICS 171
2. THE CLASSIFICATION OF STELLAR SPECTRA 179
3. HELIUM STARS 189
4. HYDROGEN STARS 197
5. SOLAR STARS 203
6. STARS WITH FLUTED SPECTRA 209
7. CARBON STARS 215
8. STARS WITH FLUTED SPECTRA SHOWING BRIGHT LINES 222
9. HELIUM STARS WITH BRIGHT LINES 229
10. WOLF-RAYET STARS 237
11. THE GENERAL QUESTION OF BRIGHT LINES IN STELLAR SPECTRA 243
12. ANOMALOUS AND VARIABLE SPECTRA 246
13. COLOUR VARIABILITY 253
14. THE SPECTRA OF DOUBLE STARS 263
15. THE EVOLUTION OF THE STARS 271
16. ROTATION OF THE STARS 280
17. SPECTROSCOPIC BINARIES 286
18. ECLIPSING STARS 299
19. SHORT-PERIOD VARIABLES 319
20. SHORT-PERIOD VARIABLES—_continued_ 328
21. THE PROBLEM OF BETA LYRÆ 337
22. STARS VARIABLE IN LONG PERIODS 347
23. PECULIAR AND IRREGULAR VARIABLES 363
24. TEMPORARY STARS 375
25. DARK STARS 399
26. THE GENERAL QUESTION OF STELLAR VARIABILITY 404
27. IRREGULAR STAR CLUSTERS 409
28. NEBULOUS CLUSTERS—THE PLEIADES 415
29. NEBULOUS CLUSTERS—_continued_ 423
30. GLOBULAR CLUSTERS 428
31. WHITE NEBULÆ 439
32. DOUBLE NEBULÆ 452
33. NEBULOUS STARS 460
34. PLANETARY NEBULÆ 469
35. ANNULAR NEBULÆ 484
36. THE ORION NEBULA 495
37. OTHER IRREGULAR NEBULÆ 506
38. NONDESCRIPT NEBULÆ 516
39. VARIABLE NEBULÆ 522
40. THE NATURE OF NEBULÆ 531
41. THE PHYSICS OF THE MILKY WAY 538
APPENDIX 547
INDEX 553

LIST OF ILLUSTRATIONS

PRINTED SEPARATELY
PLATE
I. Photograph of the Argo Nebula _Frontispiece_
II. Photograph of A-Band in Solar Spectrum
(McClean) _to face page_ 22
III. Flash and Cusp Spectra compared „ 46
IV. The Sun portrayed in Calcium Light (1);
Photograph of the Chromosphere, 31st May
1894 (2) „ 100
V. Types of the Corona (Hansky) „ 128
VI. The Corona of 1900 (Jewell) (1); Reversal and
Distortion of the C-line (Hale) (2) „ 96
VII. The Corona of 1896 (Morin) (1); the Corona of
1898 (Wesley) (2) „ 134
VIII. The Corona of 1900 (Wesley) „ 136
IX. Photographs of Typical Star-Spectra (Huggins) „ 180
X. Photographed Spectrum of ε Canis Majoris
(Lunt) (1); Photographed Spectrum of α_{2}
Centauri (Gill) (2) „ 182
XI. Spectrum of α Herculis (Espin) (1);
Photographed Spectrum of 152 Schjellerup
(Hale) (2) „ 184
XII. Photographed Spectra of Carbon Stars (Hale
and Ellerman) „ 186
XIII. Photographed Spectra of Mira and of α
Herculis (Sidgreaves) „ 188
XIV. Spectrum of γ Cassiopeiæ. Photographed by the
Rev. W. Sidgreaves „ 190
XV. Photographed Spectra of Types II., III., and
IV. compared „ 220
XVI. Sections of the Spectra of ß Lyræ and Nova
Persei „ 344
XVII. Visible Spectrum of Nova Aurigæ (Campbell) „ 376
XVIII. Nebulosity round Nova Persei (Ritchey) (1);
Spectrum of Nova Persei, 11th August 1901,
with corresponding Intensity-Curve (2) „ 394
XIX. Photograph of Messier 11 (Roberts) „ 410
XX. Photograph of a Spiral Nebula in Cetus
(Roberts) „ 442
XXI. Photograph and Drawings of a Spiral Nebula in
Pegasus (Keeler) „ 444
XXII. Photograph of Whirlpool Nebula (W. E. Wilson) „ 446
XXIII. Fan Nebulæ (Barnard) (1); Planetary Nebulæ
with their Spectra (Keeler) (2, 3, 4) „ 448
XXIV. Photograph of Owl Nebula (Roberts) (1);
Photograph of the Orion Trapezium
(Pickering) (2) „ 472
XXV. Photograph of the Ring Nebula in Lyra (W. E.
Wilson) „ 484
XXVI. Photograph of the Orion Nebula (Pickering) „ 494
XXVII. Nebulous Formation in Orion. Photographed by
W. H. Pickering „ 496
XXVIII. Photograph of the Trifid Nebula (Roberts)
(1); Photograph of Messier 77 (Roberts) (2) „ 510
XXIX. Photograph of a Nebula in Perseus (Barnard) „ 514
XXX. Photograph of the Dumb-Bell Nebula (W. E.
Wilson) „ 516
XXXI. Photograph of the Milky Way in Ophiuchus
(Barnard) „ 540

PRINTED IN THE TEXT
FIG. PAGE
1. General View of the Atmospheric Spectrum 24
2. The Infra-Red Spectrum (Langley) 24
3. Oxygen-Triplet in the Solar Spectrum 29
4. Curves representing the Distribution of Light
in Fraunhofer and Arc Lines (Jewell) 41
5. Diagram of the Helium Spectrum 57
6. Sun-spot photographed by Janssen, 1st April
1894 73
7. Photograph of a Bridged Sun-spot (Janssen) 76
8. Sun-spot drawn by J. de M. Pereira, 18th June
1894 78
9. Group of Sun-spots drawn by Miss E. Brown 78
10. Portion of a Sun-spot Spectrum photographed
by Professor Young 89
11. Reversal of the D-Lines in the Spectrum of a
Sun-spot 94
12. Prominence observed at Kalocsa, 19th
September 1893 104
13. Prominence observed at Kalocsa, 3rd October
1892 107
14. Forms of a Prominence in Hydrogen, Helium,
and Pseudo-Coronium (Fényi) 117
15. Dark Markings in the Corona of 1871 (Wesley) 134
16. Dark Markings in the Corona of 1896 (Wesley) 134
17. Spoerer’s Curves of Sun-spot Latitude 152
18. Curves of Sun-spot Frequency and Magnetic
Agitation (Ellis) 155
19. Intensity-Curves of Ηγ in Spectrum of Mira
(Campbell) 225
20. Hydrogen-Envelope of a Wolf-Rayet Star
(Campbell) 241
21. Photometric Curves of Algol Variables
(Pickering) 309
22. Light-Curve of η Aquilæ (Schur) 322
23. Orbit of η Aquilæ (Wright) 323
24. Light-Curve of S Sagittæ (Yendell) 326
25. Light and Velocity Curves of ζ Geminorum
(Campbell) 329
26. Orbit of ζ Geminorum (Campbell) 330
27. Photometric Curve of U Pegasi (Pickering) 332
28. Light-Curves of Cluster-Variables (Bailey) 336
29. Light-Curve of β Lyræ (Argelander) 337
30. System of β Lyræ (Myers) 341
31. Distribution of the Periods of 208 Variables 347
32. Light-Curve of U Orionis (Porro) 351
33. Light-Curve of S Ursæ Majoris in 1894 354
34. Mean Light-Curve of S Ursæ Majoris 355
35. Mean Light-Curve of T Ursæ Majoris 355
36. Mean Light-Curve of T Cassiopeiæ 355
37. Light-Curve of T Andromedæ 357
38. Light-Curve of S Cephei 359
39. Light-Curve of R Scuti 364
40. Long and Short Maxima of U Geminorum 365
41. Light-Curve of S^2 Cygni 367
42. Light-Curve of Nova Aurigæ 380
43. Photographs before and after the Apparition
of Nova Persei 389
44. Light-Curve of Nova Persei, 22nd February to
6th March 391
45. Light-Curve of Nova Persei, 17th March to 3rd
May 1901 391
46. Exterior Nebulosities of the Pleiades 419
47. Photograph of ω Centauri (Bailey) 430
48. Drawing of a Pair of Spindle Nebulæ
(Spitaler) 457
49. Sketch of T Tauri and Hind’s Nebula (Barnard) 524
50. Drawing from Photographs of T Tauri and
Hind’s Nebula (Keeler) 525