Library of the World's Best Literature, Ancient and Modern — Volume 02

by Unknown

Once, and once only, did Laplace launch forward, like Kepler, like Descartes, like Leibnitz, like Buffon, into the region of conjectures. But then his conception was nothing less than a complete cosmogony. All the planets revolve around the sun, from west to east, and in planes only slightly inclined to each other. The satellites revolve around their respective primaries in the same direction. Both planets and satellites, having a rotary motion, turn also upon their axes from west to east. Finally, the rotation of the sun also is directed from west to east. Here, then, is an assemblage of forty-three movements, all operating alike. By the calculus of probabilities, the odds are four thousand millions to one that this coincidence in direction is not the effect of accident.

It was Buffon, I think, who first attempted to explain this singular feature of our solar system. "Wishing, in the explanation of phenomena, to avoid recourse to causes which are not to be found in nature," the celebrated academician sought for a physical cause for what is common to the movements of so many bodies differing as they do in magnitude, in form, and in their distances from the centre of attraction. He imagined that he had discovered such a physical cause by making this triple supposition: a comet fell obliquely upon the sun; it pushed before it a torrent of fluid matter; this substance, transported to a greater or less distance from the sun according to its density, formed by condensation all the known planets. The bold hypothesis is subject to insurmountable difficulties. I proceed to indicate, in a few words, the cosmogonic system which Laplace substituted for it.

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 now revolves. No planet was then in existence. The solar nebula was endowed with a general movement of rotation in the direction west to east. As 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 its equator, as far as the limit where the centrifugal force exactly counterbalanced the attraction of the nucleus, the molecules situate at this limit ought, during the process of condensation, to separate from the rest of the atmospheric matter and to form an equatorial zone, a ring, revolving separately and with its primitive velocity. We may conceive that analogous separations were effected in the remoter strata of the nebula at different epochs and at different distances from the nucleus, and that they gave rise to a succession of distinct rings, all lying in nearly the same plane, and all endowed with different velocities.

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.

The calculus of probabilities, when confined within just limits, concerns the mathematician, the experimenter, and the statesman. From the time when Pascal and Fermat established its first principles, it has rendered most important daily services. This it is which, after suggesting the best form for statistical tables of population and mortality, teaches us to deduce from those numbers, so often misinterpreted, the most precise and useful conclusions. This it is which alone regulates with equity insurance premiums, pension funds, annuities, discounts, etc. This it is that has gradually suppressed lotteries, and other shameful snares cunningly laid for avarice and ignorance. Laplace has treated these questions with his accustomed superiority: the 'Analytical Theory of Probabilities' is worthy of the author of the 'Mécanique Céleste.'

A philosopher whose name is associated with immortal discoveries said to his too conservative audience, "Bear in mind, gentlemen, that in questions of science the authority of a thousand is not worth the humble reasoning of a single individual." Two centuries have passed over these words of Galileo without lessening their value or impugning their truth. For this reason, it has been thought better rather to glance briefly at the work of Laplace than to repeat the eulogies of his admirers.