The decisive blow to medieval ideas came from another quarter--from the Copernican astronomy. What the true theory of the earth's motion meant for philosophy has not always been rightly understood. It seems to be commonly supposed that the heliocentric system excited hostility because it degraded the earth from her proud position as centre of the universe. But the reverse is true. According to Aristotle and his scholastic followers, the centre of the universe is the lowest and least honourable, the circumference the highest and most distinguished position in it. And that is why earth, as the vilest of the four elements, tends to the centre; while fire, being the most precious, flies upward. Again, the incorruptible æther of which the heavens are composed shows its eternal character {7} by moving for ever round in a circle of which God, as Prime Mover, occupies the outermost verge. And this metaphysical topography is faithfully followed by Dante, who even improves on it by placing the worst criminals (that is, the rebels and traitors--Satan, with Judas and Brutus and Cassius) in the eternal ice at the very centre of the earth. Such fancies were incompatible with the new astronomy. No longer cold and dead, our earth might henceforth take her place among the stars, animated like them--if animated they were--and suggesting by analogy that they too supported teeming multitudes of reasonable inhabitants. But the transposition of values did not end here. Aristotle's whole philosophy had been based on a radical antithesis between the sublunary and the superlunary spheres--the world of growth, decay, vicissitude, and the world of everlasting realities. In the sublunary sphere, also, it distinguished sharply between the Forms of things, which were eternal, and the Matter on which they were imposed, an intangible, evanescent thing related to Form as Possibility to Actuality. We know that these two convenient categories are logically independent of the false cosmology that may or may not have suggested their world-wide application. But the immediate effect of having it denied, or even doubted, was greatly to exalt the credit of Matter or Power at the expense of Form or Act.