LAPLACE. IGl 



tbis triple supposition : A comet fell obliquely upon the sun ; it pushed 

 before it a torrent of fluid mutter ; this substance transported to a 

 greater or less distance from the sun, according to its mass, formed by 

 concentration all the known planets. 



The bold hypothesis of Buffon is liable to unsurmountable difiBculties. 

 I proceed to indicate, in a few words, the cosmogonic system which 

 Laplace substituted for that of the illustrious auihor of the Histoire 

 Natnrelle. 



According to Laplace, the sun was at a remote epoch the central 

 nucleus of an immense nebula, which possessed a very high temperature, 

 and extended far beyond the region in which Uranus revolves in the 

 present day. No planet was then in existence. 



The solar nebula was endued with a general movement of revolution 

 directed from west to east. At it cooled it could not fail to experience 

 a gradual condensation, and, in consequence, to rotate with greater and 

 greater rapidity. If the nebulous matter extended originally in the 

 plane of the equator as far as the limit at which the centrifugal force 

 exactly counterbalanced the attraction of the nucleus, the molecules 

 situate at this limit ought, during the process of condensation, to sepa- 

 rate from the rest of the atmospheric matter, and form an equatorial 

 zone, a ring revolving separately and with its primitive velocity. 



We may conceive that analogous separations were effected in the 

 higher strata of the nebula at different epochs, that is to say, at differ- 

 ent distances from the nucleus, and that they give rise to a succession 

 of distinct rings, included almost in the sameiilane and endued with dif- 

 ferent velocities. 



This being once admitted, it is easy to see that the indefinite stability 

 of the rings would have required a regularity of structure throughout 

 their whole contour which is very improbable. Each of them accord- 

 ingly broke in its turn into several masses, which were plainly endued 

 with a movement of rotation, coinciding in direction with the common 

 movement of revolution, and which in consequence of their fluidity as- 

 sumed spheroidal forms. 



In order, then, that one of those spheroids might absorb all the others 

 belonging to the same ring, it will be sufficient to assign to it a mass 

 greater than that of any other spheroid. 



Each of the planets, while in the vaporous condition to which we have 

 just alluded, would manifestly have a central nucleus gradually increas- 

 ing in magnitude and mass, and an atmosphere offering, at its succes- 

 sive limits, phenomena entirely similar to those which the solar atmos- 

 phere, properly so called, had exhibited. We here witness ttie birth of 

 satellites, and that of the ring of Saturn. 



The system of which I have just given an imperfect sketch has for 



its object to show how a nebula endued with a general movement of 



I rotation must eventually transform itself into a very luminous central 



nucleus (a sun) and into a series of distinct spheroidal planets, situate 



11 s 



