It is probable that, with the use of these words, there came for the first time into the consciousness of man the possibility of seeing himself purely as a solid object situated among solid objects. Of course, the Arab astronomer of the Dark and Middle Ages still saw the earth as the centre round which the universe revolved, and he would no more have dreamed of doubting the “astral” quality of the planets than the schoolmaster of to-day who instructs his pupils to write down “Let _x_ = 20 oranges” doubts whether oranges have any taste. Nevertheless we may feel pretty sure that those minds which were apparently the first to think of cutting up the sky without reference to the constellations, and which could, moreover, develop so fully the great and novel system of abstraction which they called _algebra_, did their part in bringing about that extraordinary revolution in astronomical thought which is associated with the name of Copernicus. It is true that the astronomy of Plato’s time had been intimately connected with arithmetic and geometry; but Plato’s “number” and his geometry do not appear to have been quite the abstract sciences which these things are to-day. What we call their “laws” seem to have been felt, not as intellectual deductions, but rather as real activities of soul—that human soul which, as we saw, the philosopher could not yet feel to be wholly separate from a larger world Soul, or planetary Soul. The Zodiacal signs, for instance, had been as much, if not more, classifications of this Soul as they had been sections of space. The word comes from the Greek ‘zōdion’, a little animal, and not only was every sign distinguished by a constellation, of which the majority were associated with some beast, but human character and human destiny were believed to be bound up inextricably with the position of the sun and the planets among these signs.