Page:Popular Science Monthly Volume 77.djvu/552

The work from which Kant quoted a justification of Descartes's enterprise—and, by implication, of his own—the "Universal History" (1736-65) appeared in an (incomplete) German translation in 1744. This huge historical compilation, one of the great publishing enterprises of the time, contained an introduction of (in the German edition) over one hundred pages devoted to the subject of cosmogony, giving the theories of the Greek philosophers, of Descartes, Burnet, Whiston and other moderns, and a new hypothesis of the author's own. In 1749 the first volume of a still more celebrated, and scarcely less voluminous, publication—Buffon's "Histoire Naturelle"—saw the light. This volume was chiefly devoted to a "history and theory of the earth," with a chapter on the formation of planets which contained ideas more closely related than those of Kant to the nebular hypothesis. Buffon remarked upon the peculiar uniformities of the solar system which seemed to call for a mechanical explanation, but which gravitation alone did not account for, viz., the revolution of all the planets in the same direction, approximately in the same plane, and in nearly circular orbits. Buffon's own explanation of these phenomena in his "Théorie de la Terre" of 1749 is given in the following passages:

This uniformity of position and direction in the movement of the planets necessarily presupposes some common factor in their original movement of impulsion, and makes us suspect that it has been communicated to them by one and the same cause. . . . This impulsive force was certainly imparted to the stars in general by the hand of God when he set the universe in motion. But since, in physical science, we ought to abstain so far as possible from having recourse to causes outside of nature, it seems to me that in the solar system we can account for this impelling force in a sufficiently probable manner and in accordance with the principles of mechanics. . . . May it not with some probability be imagined that a comet falling upon the surface of the sun may have separated from that body certain parts, to which it has communicated a movement of impulsion in a common direction?. . . The planets would thus have formerly belonged to the sun, and would have been detached from it by an impelling force, common to all alike, which they still retain.^[1]

Buffon was the only one^[2] of his precursors (of the post-Newtonian period) known to Laplace. He made this passage of the "Histoire Naturelle" the starting point of his own earliest exposition of his nebular hypothesis, in the concluding chapter of the "Systeme du Monde." The hypothesis of Buffon, he remarked, accounted for most of the non-gravitational peculiarities of planetary motion that require to be accounted for; but since there remained certain other such phenomena which Buffon's supposition could not explain, a new hypothesis must be devised.

Finally, in the same year, 1749, a generation after its famous

1. "Histoire Naturelle," first ed., I., pp. 131-133. Kant had read Buffon before writing his own cosmogony; see "Universal Natural History," Pt. II., ch. 2.
2. Cf. "Système du Monde," first ed., 1796, II., p. 298.