STELLAR EVOLUTION ------------------------------------------------------------------------ BY THE SAME AUTHOR. ------- CLIMATE AND TIME IN THEIR GEOLOGICAL RELATIONS: A Theory of Secular Changes of the Earth’s Climate. By JAMES CROLL, of H. M. Geological Survey of Scotland. With Maps and Illustrations. 12mo. Cloth, $2.50. DISCUSSIONS ON CLIMATE AND COSMOLOGY. By JAMES CROLL, LL.D., F.R.S. With Chart. 12mo. Cloth, $2.00. ------------------------------------------------------------------------ STELLAR EVOLUTION AND ITS RELATIONS TO GEOLOGICAL TIME BY JAMES CROLL, LL.D., F.R.S. AUTHOR OF ‘CLIMATE AND TIME,’ ‘CLIMATE AND COSMOLOGY,’ ETC. NEW YORK D. APPLETON AND COMPANY 1889 ------------------------------------------------------------------------ _Authorized Edition._ ------------------------------------------------------------------------ PREFACE. [Illustration] There are two, and only two, conceivable sources from which the prodigious amount of energy possessed by our sun and solar system can possibly have been derived. Not only are these two sources radically distinct in their essential nature, but both are admitted to be real and not merely hypothetical sources of energy. The one source is gravitation; the other, the source discussed in the present volume, a source to which attention was directed some twenty years ago. A most important distinction between these two sources is this: the amount of energy available from the former can be accurately determined, but such is not the case in regard to the latter. We can tell with tolerable certainty the greatest amount of energy which gravitation could possibly have conferred on the sun and solar system; but we have, at present, no means of assigning a limit to the possible amount which might have been derived from the other source. It may have been equal to that which gravitation could afford, or it may have been twofold, fourfold, or even tenfold that amount. We have evidently in this case a means of determining which of the two sources will ultimately have to be adopted as the source to which the energy of our solar system must be referred. For if it can be proved from the admitted facts of geology, biology, and other sciences, that the amount of energy in the form of heat which has been radiated into space by the sun during geological time is far greater than the amount which could possibly have been derived from gravitation, this will undoubtedly show that gravitation cannot account for the energy originally possessed by our system.