Leucippus and his more famous disciples, Democritus and Epicurus, were the first who ventured to trace the mechanical history of the cosmos. Their primordial atoms were endowed with weight, and it was weight or gravity which ultimately determined their spacial arrangement and mutual relations. Rectilinear in the first draft of the scheme, their movements were somewhat arbitrarily deflected by Epicurus; and the gyrations thence ensuing eventually became, so to speak, authentic and precise in the Cartesian vortices and in Swedenborg's solar maelstrom. Kant's _Natural History_ of the universe was another, though an entirely separate branch of the atomistic stock. The Democritean atoms, however, and in a lesser degree the Kantian atoms, differed essentially from the ultimates of chemical analysis postulated by Dalton. They were a scratch lot--an incongruous assortment of fragments, rather than of elementary portions of matter, indefinitely various in size, shape, and mass. Nor was this diversity created as a mere play of fancy. It was strictly necessary to the plan of action adopted. For, apart from heterogeneity, there could obviously be no development. Absolute uniformity involves absolute permanence. Change can originate only through inequality. There must be a tilt of level before the current will begin to flow; some cause of predominance is needed to set it going in a given direction. Here, of a surety, is the initial crux of all cosmogonists. They usually surmount it by assuming the occurrence of casual condensations, secure against disproof, while incapable of verification. The expedient thus begs the question. Theories of world-history made an integral part of antique philosophy. Each founder of a school aimed at establishing a complete system of knowledge, co-extensive with phenomena, embracing all things, from the _primum mobile_ overhead to the blade of grass underfoot, and rationalizing the past, present, and future of the comprehensive whole. Modern science is less ambitious. Aspiring to no such vast synthesis, it is content to make laborious acquaintance with the facts of nature, to ponder their implications, and, if possible, to reconstruct on the basis supplied by them the condition of things in the 'dim backward' of unmeasured time. By no such means, it is true, can their beginning in any real sense be arrived at; the weapons of induction become blunted long before they strike home to the heart of that mystery; yet the recognition of their inadequacy brings compensation in a fuller mastery over their properly adapted use. Science, so called, was, indeed, down to the Baconian era, a turbid mixture of physics with metaphysics. The solution, it might be said, was attempted of an insoluble material which refused to dissolve and was hindered from precipitating.