Those who will may see in all this an anticipation of chemical substitution and double decomposition. We can assure them that it will be by no means the most absurd parallel discovered between ancient and modern ideas. It is possible, however, to trace a more real connexion between the Aristotelian physics and mediaeval thought. We do not of course mean the scholastic philosophy, for there never was the slightest doubt as to its derivation; we allude to the alchemy and astrology which did duty for positive science during so many centuries, and even overlapped it down to the time of Newton, himself an ardent alchemist. The superstitions of astrology originated independently of the peripatetic system, and probably long before it, but they were likely to be encouraged by it instead of being repressed, as they would have been by a less anthropomorphic philosophy. Aristotle himself, as we have seen, limited the action of the heavens on the sublunary sphere to their heating power; but, by crediting them with an immortal reason and the pursuit of ends unknown to us, he opened a wide field for conjecture as to what those ends were, and how they could be ascertained. That the stars and planets were always thinking and acting, but never about our affairs, was not a notion likely to be permanently accepted. Neither was it easy to believe that their various configurations, movements, and names (the last probably revealed by themselves) were entirely without significance. From such considerations to the casting of horoscopes is not a far remove. The Aristotelian chemistry would still more readily lend itself to the purposes of alchemy. If Nature is one vast process of transmutation, then particular bodies, such as the metals, not only may, but must be convertible into one another. And even those who rejected Aristotle’s logic with scorn still clung to his natural philosophy when it flattered their hopes of gain. Bacon kept the theory of substantial forms. His originality consisted in looking for a method by which any form, or assemblage of forms might be superinduced at pleasure on the underlying matter. The real development of knowledge pursued a far different course. The great discoverers of the sixteenth and seventeenth centuries achieved their success by absolutely reversing the method of Aristotle, by bringing into fruitful contact principles which he had condemned to barren isolation. They carried terrestrial physics into the heavens; they brought down the absoluteness and eternity of celestial law to earth; they showed that Aristotle’s antithetical qualities were merely quantitative distinctions. These they resolved into modes of motion; and they also resolved all motions into one, which was both rectilinear and perpetual. But they and their successors put an end to all dreams of transmutation, when they showed by another synthesis that all matter, at least within the limits of our