the end of a period of contraction it is gathered up in a solid globe: at the end of a period of expansion it is diffused throughout space in a state of tenuity which nowadays we might describe as gaseous. And this gigantic see-saw motion of the universe as a whole has gone on and will go on for ever and ever.(917) (M223) The imposing generalisation thus formulated by Empedocles in the fifth century before our era was enunciated independently in the nineteenth century of our era by Herbert Spencer. Like his Greek predecessor, the modern English philosopher held that the material universe passes through alternate periods of concentration and dissipation, of evolution and dissolution, according as the forces of attraction and repulsion alternately prevail. The terms in which he sums up his general conclusions might be used with hardly any change to describe the conclusions of Empedocles. For the sake of comparison it may be well to subjoin the passage. It runs as follows:— “Thus we are led to the conclusion that the entire process of things, as displayed in the aggregate of the visible Universe, is analogous to the entire process of things as displayed in the smallest aggregates. “Motion as well as matter being fixed in quantity, it would seem that the change in the distribution of Matter which Motion effects, coming to a limit in whichever direction it is carried, the indestructible Motion thereupon necessitates a reverse distribution. Apparently, the universally coexistent forces of attraction and repulsion, which, as we have seen, necessitate rhythm in all minor changes throughout the Universe, also necessitate rhythm in the totality of its changes—produce now an immeasurable period during which the attractive forces predominating, cause universal concentration, and then an immeasurable period during which the repulsive forces predominating, cause universal diffusion—alternate eras of Evolution and Dissolution. And thus there is suggested the conception of a past during which there have been successive Evolutions analogous to that which is now going on; and a future during which successive other such Evolutions may go on—ever the same in principle but never the same in concrete result.”(918)