ON THE FORMATION OF NEBULA. 343 



to the present time, the path pointed out by the illustrious Laplace will 

 be closely followed. 



More recent writers have suggested other modes for the formation 

 of such systems, some of which, however, would seem to be the excep- 

 tion instead of the rule here presented, as the sequel will show. 



No definite explanation will be given in this paper as to how the 

 out-thrown masses of nebulous matter which will hereinafter be de- 

 scribed may be utilized in forming other systems ; and no suggestion 

 given as to the formation or structure of the globular or other clusters 

 of stars, which are so bewildering to investigate, and yet so interesting 

 to look upon ; but the formation of these, and of that great galaxy of 

 stars of which our sun seems to be a member, may be accounted for on 

 the same dynamical principles that are employed in this discussion. 



Following Laplace, it is assumed, then, that our planetary system 

 began its evolutions as a great nebulous sphere of perfectly dissociated 

 matter of almost inconceivable rarity, and of nearly uniform density. 



At this time it was not quiescent, but most probably was agitated 

 by the movement of internal currents and counter-currents, the resultant 

 motion of which caused the entire mass to revolve around one of its 

 diameters. 



From the nature of the case, this rotation must have been very slow 

 indeed, probably one rotation in millions of years. If its diameter were 

 500 times that of Neptune's present orbit, it would require more than 

 36,000,000 years to make one revolution ; even this velocity would 

 slightly flatten it at the poles. 



During these revolutions it was radiating heat, not only from its 

 surface, but, on account of its extreme rarity, 1 from regions far below 

 its surface. This radiation, combined with the gravitation of its parts, 

 caused contraction ; and this contraction, by well-known mechanical 

 laws, increased the rate of rotation, and a consequent further flattening 

 at the poles, while a correspondingly greater increase of density in the 

 central parts took place. 



This process continued till the rate of rotation of the bulging equa- 

 torial belt generated sufficient tangential force, by virtue of the rapid 

 rotation of those particles, to counterbalance the gravitating force of 

 the disk-like mass within, at which time further contraction of the outer 

 edge of this nebulous belt, or beginning of a ring, ceased, except that 

 infinitesimal portion due to resistance alone ; for, at this time, each par- 

 ticle in this outer belt revolved in its own orbit around the central mass. 



As radiation continued, contraction also continued, thereby confer- 

 ring a planetary character on each particle of the successive layers of 

 the equatorial ring of particles thus left out by the contracting nebulous 

 spheroid. 



Let us now confine our attention, to this out-left ring, for its conduct 



1 It should be here remarked that the heat thus radiated from the nebula is not lost, 

 but continues as wave-motion in the ether, uutil it is again converted into molecular mo- 

 tion in ponderable matter. 



