Page:Popular Science Monthly Volume 17.djvu/478

462 Swedenborg postulates a solar vortex, from which is gradually detached a ring, by the disruption of which the planetary globes and their satellites are formed. Twenty years later analogous ideas were held by Immanuel Kant, who, it would seem, merely commented on and developed the views of Thomas Wright. In this system the planets are formed directly by the condensation of nebulous matter without the intermediate formation of rings. These theories are curious in the light of the history of science. There is also the theory of Buffon, who imagined that a comet, striking the sun, forced from it a stream of matter that agglomerated to form the planets. But Laplace was the first to offer a theory of the origin of the solar system that was founded on rigorously scientific principles, and that conformed to the data of celestial mechanics. That which distinguishes the conceptions of his genius is, that the discoveries since made, far from weakening his hypothesis, seem on the contrary to daily strengthen it.

Laplace conceived all the stars formed by the gradual concentration of a nebulosity diffused in space, which became luminous in proportion as it condensed, under the force of gravitation. The sun itself was at first nebulous, with a brilliant nucleus. Supposing the system endowed with a rotary movement—and this is an unavoidable postulate—the solar atmosphere at first assumed a figure of spheroidal equilibrium, much flattened, and limited in its dimensions by the zone where the centrifugal force counterbalanced the weight. The molecules situated beyond this limit ceased to belong to the atmosphere proper, and revolved freely around the central star as planetary masses. Now, a law of mechanics teaches that in proportion as the cooling contracts the atmosphere and condenses the molecules in the vicinity of the nucleus, the rotation becomes more rapid; the centrifugal force thereby augmenting, the point where the weight counterbalances it is brought nearer the center, and the particles banished to the outskirts become planets. Contracting little by little, the solar atmosphere became separated from the zone of vapors in the plane of its equator. These abandoned vapors, wrecks of the solar ocean, must first have formed concentric rings circulating around the sun, comparable to the rings of Saturn. These rings would soon break up into several masses, which, speedily conglobulating, assumed, a rotary movement in the direction of their revolution around the sun. It is thus that the planets originate, and give birth, in cooling, to the satellites that accompany them. "Hence," says Laplace, "the notable phenomenon of the slight eccentricity of the orbits of the planets and their satellites; of the slight inclination of these orbits to the plane of the solar equator; and of the identity of movement, in rotation and revolution, of all these bodies with that of the sun, giving to the hypothesis we offer a high degree