author's death, the "Protogæa" of Leibniz was published. In this Leibniz contended, on grounds now familiar enough, that the earth must have originally been in a fluid and intensely heated state; that through the cooling of the surface a solid crust was formed and the viscous fiery substance of the globe concentrated in the interior; that the present earth-structure is due to the successive action in the past of fire (fusion) and water (sedimentation); and that the existence of fossils testifies to the extinction of once flourishing species of animals, in consequence of modifications of the earth's surface due to one or the other of these agencies.
For comparison with the hypotheses of his precursors and successors, Kant's own scheme of cosmogony must now be indicated in its more essential features. He assumes for a starting point a "state of nature which is the very simplest that could follow upon nonentity," namely, a chaos in which all the matter in the universe was scattered throughout infinite space. It somehow "filled" the whole of that space, and yet its component particles were infinitely more diffused than now; Kant expressly declares that space was once "full," and is now "empty," except for the actual celestial bodies. The original particles were not all alike; they differed in "specific density and force of attraction." Consequently, when the universe is once permitted to begin active business, "the scattered elements of the denser sort, by virtue of their attraction, gather together out of the space surrounding them all the matter of less specific gravity; these elements in turn, with the material which has united with them, collect in points where the particles of a yet denser kind are found"; and so on.
If we follow in imagination this process by which nature fashions itself into form throughout the whole extent of chaos, we easily perceive that the sole result of this process would consist finally in the agglomeration of divers masses which, when their formation was complete, would be forever at rest and unmoved.
Fortunately, nature has other forces at her command; besides gravitation, there is also operative a force of repulsion, which shows itself "especially when matter is decomposed into fine particles." By this force the elements, "as they fall towards the attracting body are deflected by one another and have their perpendicular fall converted into a movement of revolution." Having indicated the two general working principles of his cosmical mechanics, Kant now judiciously leaves the problem of the genesis of a universe, and turns somewhat abruptly to the simpler problem of the formation of our solar system, from the solution of which "we shall be able by analogy to infer a similar mode of origination in the case of the larger world-systems."
The lesser process, as Kant conceives it, may be said to fall into four stages: (1) The formation of the nucleus of a sun. There is formed at the point of maximum attraction of a given region of space, "a body which, so to say, grows from an infinitely small germ, at first
