“Sate ae 
_ NEBULAR THEORY. 361 
_ We have just found, conformably to the principles of 
mechanics, the forces with which the particles of the 
nebula were originally endued, in the movements of rota- 
tion and revolution of the compact and distinct masses 
which these particles have brought into existence by 
their condensation. But we have thereby achieved only 
a single step. The primitive movement of rotation of 
the nebula is not connected with the simple attraction of 
the particles. ‘This movement seems to imply the action 
of a primordial impulsive force. 
Laplace is far from adopting, in this respect, the almost 
universal opinion of philosophers and mathematicians. 
He does not suppose that the mutual attractions of orig- 
inally immovable bodies must ultimately reduce all the 
bodies to a state of rest around their common centre of 
gravity. He maintains, on the contrary, that three bodies, 
in a state of rest, two of which have a much greater mass 
than the third, would concentrate into a single mass only 
in certain exceptional cases. In general, the two most 
considerable bodies would unite together, while the third 
would revolve around their common centre of gravity. 
Attraction would thus become the cause of a sort of 
movement which would seem to be explicable solely by 
an impulsive force. 
It might be supposed, indeed, that in explaining this 
part of his system Laplace had before his eyes the words 
which Rousseau has placed in the mouth of the vicar of 
Savoy, and that he wished to refute them: “ Newton 
has discovered the law of attraction,” says the author 
of Emile, “but attraction alone would soon reduce the 
universe to an immovable mass: with this law we must 
combine a projectile force in order to make the celestial 
bodies describe curve lines. Let Descartes reveal to us 
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