The First Part of the volume is devoted to the consideration of what I believe to be the probable origin of meteorites, comets, and nebulæ, and of the real source from which our sun derived his energy. The facts which support the theory here advocated, together with the light which that theory appears to cast upon those facts, are next considered; and it will be found, I think, that the theory has been very much strengthened by the recent important spectroscopic researches of Mr. Lockyer and others in reference to the constitution of nebulæ. The Second Part of the work deals with the evidence in support of the theory derived from the testimony of geology and biology as to the age of the sun’s heat. The Third, and last, Part has been devoted to questions relating to the pre-nebular condition of the universe, and the bearing which these have on theories of stellar evolution. Several subjects introduced in this part are only very briefly treated. These will, however, be considered at greater length in a future volume, “Determinism, not Force, the Foundation-stone of Evolution,” a work of a more general and abstract character, which was commenced many years ago. PERTH: _January 2, 1889_. ------------------------------------------------------------------------ CONTENTS. [Illustration] ------------------------------------------------------------------------ PART I. _THE IMPACT THEORY OF STELLAR EVOLUTION._ PAGE CONSIDERATION OF THE FACTS WHICH SUPPORT THE THEORY, AND OF THE LIGHT WHICH THE THEORY APPEARS TO CAST UPON THE FACTS 12 I. Probable Origin of Meteorites 12 II. Motion of the Stars; how of such different velocities, and always in straight lines 14 III. Motion of the Stars not due to their mutual attractions 14 IV. Probable Origin of Comets 17 V. Nebulæ 18 1. Origin of Nebulæ 18 2. How Nebulæ occupy so much space 18 3. Why Nebulæ are of such various shapes 19 4. Broken fragments in a Gaseous mass of an excessively high temperature the First stage of a Nebula 19 5. The Gaseous condition the Second stage of a Nebula 24 6. The Gaseous condition Essential to the Nebular Hypothesis 25 7. The mass must have possessed an excessive temperature 26