STELLAR EVOLUTION
Climate and Time in their GeologicalRelations: A Theory of Secular Changesof 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. WithChart. 12mo. Cloth, $2.00.
There are two, and only two, conceivable sources fromwhich the prodigious amount of energy possessed byour sun and solar system can possibly have beenderived. Not only are these two sources radicallydistinct in their essential nature, but both are admittedto be real and not merely hypothetical sources ofenergy. The one source is gravitation; the other,the source discussed in the present volume, a sourceto which attention was directed some twenty yearsago. A most important distinction between these twosources is this: the amount of energy available fromthe former can be accurately determined, but such isnot the case in regard to the latter. We can tell withtolerable certainty the greatest amount of energywhich gravitation could possibly have conferred onthe sun and solar system; but we have, at present,no means of assigning a limit to the possible amountwhich might have been derived from the other source.It may have been equal to that which gravitationcould afford, or it may have been twofold, fourfold, oreven tenfold that amount.
We have evidently in this case a means of determiningwhich of the two sources will ultimately haveto be adopted as the source to which the energy of oursolar system must be referred. For if it can be provedfrom the admitted facts of geology, biology, and othersciences, that the amount of energy in the form ofheat which has been radiated into space by the sunduring geological time is far greater than the amountwhich could possibly have been derived from gravitation,this will undoubtedly show that gravitation cannotaccount for the energy originally possessed by oursystem.
The First Part of the volume is devoted to theconsideration of what I believe to be the probableorigin of meteorites, comets, and nebulæ, and of thereal source from which our sun derived his energy.The facts which support the theory here advocated,together with the light which that theory appears