This being once admitted, it is easy to see that the permanent stability of the rings would have required a regularity of structure throughout their whole contour, which is very improbable. Each of them, accordingly, broke in its turn into several masses, which were obviously endowed with a movement of rotation coinciding in direction with the common movement of revolution, and which, in consequence of their fluidity, assumed spheroidal forms. In order, next, that one of those spheroids may absorb all the others belonging to the same ring, it is sufficient to suppose it to have a mass greater than that of any other spheroid of its group. Each of the planets, while in this vaporous condition to which we have just alluded, would manifestly have a central nucleus, gradually increasing in magnitude and mass, and an atmosphere offering, at its successive limits, phenomena entirely similar to those which the solar atmosphere, properly so called, had exhibited. We are here contemplating the birth of satellites and the birth of the ring of Saturn. The Nebular Hypothesis, of which I have just given an imperfect sketch, has for its object to show how a nebula endowed with a general movement of rotation must eventually transform itself into a very luminous central nucleus (a sun), and into a series of distinct spheroidal planets, situate at considerable distances from one another, all revolving around the central sun, in the direction of the original movement of the nebula; how these planets ought also to have movements of rotation in similar directions; how, finally, the satellites, when any such are formed, must revolve upon their axes and around their respective primaries, in the direction of rotation of the planets and of their movement of revolution around the sun. In all that precedes, attention has been concentrated upon the 'Mécanique Céleste.' The 'Système du Monde' and the 'Théorie Analytique des Probabilités' also deserve description. The Exposition of the System of the World is the 'Mécanique Céleste' divested of that great apparatus of analytical formulae which must be attentively perused by every astronomer who, to use an expression of Plato, wishes to know the numbers which govern the physical universe. It is from this work that persons ignorant of mathematics may obtain competent knowledge of the methods to which physical astronomy owes its astonishing progress. Written with a noble simplicity of style, an exquisite exactness of expression, and a scrupulous accuracy, it is universally conceded to stand among the noblest monuments of French literature.... The labors of all ages to persuade truth from the heavens are there justly, clearly, and profoundly analyzed. Genius presides as the impartial judge of genius. Throughout his work Laplace remained at the height of his great mission. It will be read with respect so long as the torch of science illuminates the world.