1887.] on the Sim's Heat. 17 



The moment of momentum of the whole solar system is about 

 eighteen times that of the sun's rotation ; seventeen-eighteenths being 

 Jupiter's and one-eighteenth the Sun's, the other bodies being not 

 worth taking into account in the reckoning of moment of momentum. 



Now instead of being absolutely at rest in the beginning, let the 

 twenty-nine million moons be given each with some small motion, 

 making ujd in all an amount of moment of momentum about a certain 

 axis, equal to the moment of momentum of the solar system which we 

 have just been considering ; or considerably greater than this, to allow 

 for effect of resisting medium. They will fall together for two 

 hundred and fifty years, and though not meeting precisely in the 

 centre as in the first supposed case of no primitive motion, they 

 will, two hundred and fifty years from the beginning, be so crowded 

 together that there will be myriads of collisions, and almost every 

 one of the twenty-nine million globes will be melted and driven 

 into vapour by the heat of these collisions. The vapour or gas 

 thus generated will fly outwards, and after several hundreds or 

 thousands of years of outward and inward oscillatory motion, may 

 settle into an oblate rotating nebula extending its equatorial ra- 

 dius far beyond the orbit of Neptune, and with moment of momentum 

 equal to or exceeding the moment of momentum of the solar 

 system. This is just the beginning postulated by Laj)lace for 

 his nebular theory of the evolution of the solar system ; which, 

 founded on the natural history of the stellar universe, as ob- 

 served by the elder Herschell, and completed in details by the 

 profound dynamical judgment and imaginative genius of Laplace, 

 seems converted by thermodynamics into a necessary truth, if we 

 make no other uncertain assumption than that the materials at present 

 constituting the dead matter of the solar system have existed under 

 the laws of dead matter for a hundred million years. Thus there may 

 in reality be nothing more of mystery or of difficulty in the automatic 

 progress of the solar system from cold matter diffused through 

 space, to its present manifest order and beauty, lighted and warmed 

 by its brilliant sun, than there is in the winding up of a clock* and 

 letting it go till it stops. I need scarcely say that the beginning and 

 the maintenance of life on the earth is absolutely and infinitely 

 beyond the range of all soimd speculation in dynamical science. The 

 only contribution of dynamics to theoretical biology is absolute 

 negation of automatic commencement or automatic maintenance of 

 life. 



I shall only say in conclusion : — Assuming the sun's mass to be 

 composed of materials which were far asunder before it was hot, the 

 immediate antecedent to its incandescence must have been either two 

 bodies with details differing only in proportions and densities from 



* Even in tins, and all the properties of matter which it involves, there is 

 enough, and more than enough, of mystery to our limited understanding. A 

 watch-spring is much farther beyond our understanding than is a gaseous nebula. 



Vol. XII. (No. 81.) c 



