of democracy, kingship, and aristocracy (or the rule of the best). Such, then, are the statements they make in their ethical doctrines, with much more besides, together with their proper proofs : let this, however, suffice for a statement of them in a summary and elementary form. Their physical doctrine they divide into sections (1) about bodies ; (2) about principles ; (3) about elements ; (4) about the gods : (5) about bounding surfaces and space whether filled or empty. This is a division into species ; but the generic division is into three parts, dealing with (i.) the universe ; (ii.) the elements ; (iii.) the subject of causation. The part dealing with the universe admits, they say, of division into two : for with one aspect of it the mathematicians also are concerned, in so far as they treat questions relating to the fixed stars and the planets, e.g. whether the sun is or is not just so large as it appears to be, and the same about the moon, the question of their revolutions, and other inquiries of the same sort. But there is another aspect or field of cosmological ° inquiry, which belongs to the physicists alone : this includes such questions as what the substance of the universe is, whether the sun and the stars are made up of form and matter, whether the world has had a beginning in time or not, whether it is animate or inanimate, whether it is destructible or indestructible, whether it is governed by providence, and all the rest. The part concerned with causation, again, is itself subdivided into two. And in one of its aspects medical inquiries have a share in it, in so far as it involves investigation of the ruling principle of the soul and the phenomena of