and regular working out of preordained physical laws, in accordance with which they have each naturally assumed, by pure force of circumstances, their existing size, and weight, and orbit, and position. Geology has applied a similar conception to the origin and becoming of the earth's material and external features as we now know them. Accepting from astronomy the notion of our planet's primary condition as a cooling sphere of incandescent matter, it goes on to show how the two great envelopes, atmospheric and oceanic, gaseous and liquid, have gradually formed around its solid core; how the hard crust of the central mass has been wrinkled and corrugated into mountain chain and deep-cut valley, uplifted here into elevated table-land or there depressed into hollow ocean bed; how sediment has slowly gathered on the floor of the sea, and how volcanic energies or lateral pressure have subsequently forced up the resulting deposits into Alpine peaks and massive continents. In this direction, it was Lyell who principally introduced into science the uniformitarian or evolutionary principle, who substituted for the frequent cataclysms and fresh beginnings of the earlier geologists the grand conception of continuous action, producing from comparatively infinitesimal but cumulative causes effects which at last attain by accretion the most colossal proportions. Here biology next steps in, with its splendid explanation of organic life, as due essentially to the secondary action of radiated solar energy on the outer crust of such a cooling and evolving planet. Falling on the cells of the simplest green plants, the potent sunlight dissociates the carbon from the oxygen in the carbonic acid floating in the atmosphere, and builds it up with the hydrogen of water in the tissues of the organism into starches and other organic products, which differ from the inert substances around them, mainly by the possession of locked-up solar energy. On the energy-yielding food-stuffs thus stored up the animal in turn feeds and battens, reducing what was before potential into actual motion, just as the steam-engine reduces the latent solar energy of coal into visible heat and visible movement in its furnace and its machinery. How the first organism came to exist biology has not yet been able fully to explain for us; but aided by chemical science it has been able to show us in part how some of the simpler organic bodies may have been originally built up, and it does not despair of showing us in the end how the earliest organism may actually have been produced from the prime elements of oxygen, hydrogen, nitrogen, and carbon. Into this most fundamental of biological problems, however, Darwin himself, with his constitutional caution and dread of speculative theorising, was not careful or curious to enter. Even upon the far less abstruse and hypothetical question, whether all life took its prime origin from a single starting-point or from several distinct