Book contents
- Frontmatter
- PREFACE
- Contents
- ILLUSTRATIONS
- ADDENDA
- CHAPTER I THE TASK OF SIDEREAL ASTRONOMY
- CHAPTER II THE METHODS OF SIDEREAL RESEARCH
- CHAPTER III SIRIAN AND SOLAR STARS
- CHAPTER IV STARS WITH BANDED SPECTRA
- CHAPTER V GASEOUS STARS AND NEBULÆ
- CHAPTER VI SIDEREAL EVOLUTION
- CHAPTER VII TEMPORARY STARS
- CHAPTER VIII VARIABLE STARS OF LONG PERIOD
- CHAPTER IX VARIABLE STARS OF SHORT PERIOD
- CHAPTER X THE COLOURS OF THE STARS
- CHAPTER XI DOUBLE STARS
- CHAPTER XII VARIABLE DOUBLE STARS
- CHAPTER XIII STELLAR ORBITS
- CHAPTER XIV MULTIPLE STARS
- CHAPTER XV THE PLEIADES
- CHAPTER XVI STAR CLUSTERS
- CHAPTER XVII THE FORMS OF NEBULÆ
- CHAPTER XVIII THE GREAT NEBULÆ
- CHAPTER XIX THE NATURE AND CHANGES OF NEBULÆ
- CHAPTER XX THE DISTANCES OF THE STARS
- CHAPTER XXI TRANSLATION OF THE SOLAR SYSTEM
- CHAPTER XXII THE PROPER MOTIONS OF THE STARS
- CHAPTER XXIII THE MILKY WAY
- CHAPTER XXIV STATUS OF THE NEBULÆ
- CHAPTER XXV THE CONSTRUCTION OF THE HEAVENS
- APPENDIX.—TABLES OF STELLAR DATA
- INDEX
- Plate section
CHAPTER XIX - THE NATURE AND CHANGES OF NEBULÆ
Published online by Cambridge University Press: 05 July 2011
- Frontmatter
- PREFACE
- Contents
- ILLUSTRATIONS
- ADDENDA
- CHAPTER I THE TASK OF SIDEREAL ASTRONOMY
- CHAPTER II THE METHODS OF SIDEREAL RESEARCH
- CHAPTER III SIRIAN AND SOLAR STARS
- CHAPTER IV STARS WITH BANDED SPECTRA
- CHAPTER V GASEOUS STARS AND NEBULÆ
- CHAPTER VI SIDEREAL EVOLUTION
- CHAPTER VII TEMPORARY STARS
- CHAPTER VIII VARIABLE STARS OF LONG PERIOD
- CHAPTER IX VARIABLE STARS OF SHORT PERIOD
- CHAPTER X THE COLOURS OF THE STARS
- CHAPTER XI DOUBLE STARS
- CHAPTER XII VARIABLE DOUBLE STARS
- CHAPTER XIII STELLAR ORBITS
- CHAPTER XIV MULTIPLE STARS
- CHAPTER XV THE PLEIADES
- CHAPTER XVI STAR CLUSTERS
- CHAPTER XVII THE FORMS OF NEBULÆ
- CHAPTER XVIII THE GREAT NEBULÆ
- CHAPTER XIX THE NATURE AND CHANGES OF NEBULÆ
- CHAPTER XX THE DISTANCES OF THE STARS
- CHAPTER XXI TRANSLATION OF THE SOLAR SYSTEM
- CHAPTER XXII THE PROPER MOTIONS OF THE STARS
- CHAPTER XXIII THE MILKY WAY
- CHAPTER XXIV STATUS OF THE NEBULÆ
- CHAPTER XXV THE CONSTRUCTION OF THE HEAVENS
- APPENDIX.—TABLES OF STELLAR DATA
- INDEX
- Plate section
Summary
Speculations as to an identity of nature between nebulæ and comets are no novelty; they presented themselves, as they could hardly fail to do, to the mind of Sir William Herschel; but some consistency was first given to them by the recent experimental researches of Mr. Lockyer. It is true that the results of light analysis are far from being decisive in their favour. The spectra of the two classes of bodies are fundamentally unlike. No gaseous nebula gives a trace of the carbon-bands which characterise nearly all comets; and no comet has yet furnished any direct evidence of the presence of hydrogen among its constituents. Moreover, nebulæ (apart from the stars contained in them) seem to emit no genuinely continuous light, while cometary nuclei glow in the ordinary manner of white-hot solid and liquid substances. Traces of a spectroscopic analogy can indeed be shown to exist; but they are met with only in the secondary elements of each spectrum. The resemblance seems only incidental; the dissimilarity essential.
This does not, however, detract from the closeness of a physical analogy, the deep import of which cannot be too forcibly dwelt upon. Both comets and nebulæ consist of enormous volumes of gaseous material, controlled by nuclear condensations, whether of the same or of a different nature in the two genera we need not now stop to inquire. Both, there is the strongest reason to believe, shine through the effects of electrical excitement.
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- The System of the Stars , pp. 285 - 296Publisher: Cambridge University PressPrint publication year: 2010First published in: 1890