We cannot doubt that the solar system, as we see it, is the result of some process of growth–that, during innumerable ages, the forces of Nature were at work upon its materials, blindly modelling them into the shape appointed for them from the beginning by Omnipotent Wisdom. To set ourselves to inquire what that process was, may be an audacity, but it is a legitimate, nay, an inevitable one. For man's implanted instinct to “look before and after” does not apply to his own little life alone, but regards the whole history of creation, from the highest to the lowest–from the microscopic germ of an alga or a fungus to the visible frame and furniture of the heavens.

Kant considered that the inquiry into the mode of origin of the world was one of the easiest problems set by Nature; but it cannot be said that his own solution of it was a satisfactory one. He, however, struck out in 1755 a track which thought still pursues. In his Allgemeine Naturgeschichte the growth of sun and planets was traced from the cradle of a vast and formless mass of evenly diffused particles, and the uniformity of their movements was sought to be accounted for by the uniform action of attractive and repulsive forces, under the dominion of which their development was carried forwards.