312 The Nebular Hypothesis of Laplace. 



which, tends more and more to make the molecule approach 

 the equator, in proportion as the centrifugal force is increased. 

 The increase of angular velocity in the rotation therefore 

 causes the surface molecules to move from all parts' towards 

 its equator, and then to be abandoned into space as we have 

 described." 



" It will be understood that our nebula, in its process of 

 cooling, has thus abandoned successively, in the plane of its 

 equator, divers rings of nebulous matter, which continue to 

 revolve in the same plane, and about a common centre. The 

 central mass to which successive condensations have reduced 

 the nebula, is no other than the sun ; and the concentric rings 

 of nebulous matter thrown off in succession in the plane of its 

 equator will give rise to planets, as we shall proceed, to show." 



" Each ring must be perfectly regular, in order to preserve 

 its annular form for an indefinite time. This regularity can 

 only exist under exceptional circumstances, and it is natural 

 to suppose they are wanting in the case before us. Thus the 

 matter belonging to each tends to assemble about certain 

 centres of attraction, and their partial condensation divides the 

 ring into fragments, which continue to move separately very 

 much as they did when united. The velocity of the various 

 parts which once formed one ring not being rigorously the 

 same, either because they were not equal at the moment of 

 separation, or were subsequently changed by the perturbing 

 action to which the whole system is exposed, it follows that 

 the different portions can rejoin each other, and end in forming 

 a single mass, circulating round the sun in an orbit nearly cor- 

 responding with the circumference of the ring from which it 

 originated, and this mass condenses itself into a planet. It 

 may, however, happen that the various fragments into which a 

 ring was decomposed will continue to revolve as separate 

 bodies, and give rise to many distinct planets moving in almost 

 the same orbits, and it is thus that the planetoids between 

 Mars and Jupiter may have resulted from the fragments into 

 which one nebulous ring may have been divided." 



" Let us now see what becomes of the materials of an entire 

 ring, united together about one point of its circumference as 

 we have supposed, and let us endeavour to understand how 

 the mass thus formed has been able to produce a planet turning 

 upon its own axis, and accompanied by satellites, as is gene- 

 rally the case in our planetary system. In the progressive 

 condensation of such a mass, the molecules most remote from 

 the sun have approached nearer to that body, and the mole- 

 cules which were nearest have become more remote ; the first 

 having a greater, and the latter a smaller velocity, than that 

 of the mean portions towards which they are moving by the 



