the universe; and seeing light bodies move up, he credited them with an equal and opposite tendency to the circumference of the universe, which, like Parmenides and Plato, he believed to be of finite extent. Thus each kind of matter has its appropriate place, motion to which ends in rest, while motion away from it, being constrained, cannot last. Accordingly, the constant periodicity of terrestrial phenomena necessitates as constant a transformation of dry and wet, and of hot and cold bodies into one another. This is explained with perfect accuracy by the diurnal and annual revolutions of the sun. Here, however, we are introduced to a new kind of motion, which, instead of being rectilinear and finite, is circular and eternal. To account for it, Aristotle assumes a fifth element entirely different in character from the four terrestrial elements. Unlike them, it is absolutely simple, and has a correspondingly simple mode of motion, which, as our philosopher erroneously supposes, can be no other than circular rotation. Out of this eternal unchanging divine substance, which he calls aether, are formed the heavenly bodies and the transparent spheres containing them. But there is something beyond it of an even higher and purer nature. Aristotle proves, with great subtlety, from his fundamental assumptions, that the movement of an extended substance cannot be self-caused. He also proves that motion must be absolutely continuous and without a beginning. We have, therefore, no choice but to accept the existence of an unextended, immaterial, eternal, and infinite Power on which the whole cosmos depends. So much only is established in the _Physics_. Further particulars are given in the twelfth book of the _Metaphysics_. There we learn that, all movement being from possibility to actuality, the source of movement must be a completely realised actuality—pure form without any admixture of matter. But the highest form known to us in the ascending scale of organic life is the human soul, and the highest function of soul is reason. Reason then must be that which moves without being moved itself, drawing all things upwards and onwards by the love which its perfection inspires. The eternal, infinite, absolute actuality existing beyond the outermost starry sphere is God. Aristotle describes God as the thought which thinks itself and finds in the simple act of self-consciousness an everlasting happiness, wonderful if it always equals the best moments of our mortal life, more wonderful still if it surpasses them. There is only one supreme God, for plurality is due to an admixture of matter, and He is pure form. The rule of many is not good, as Homer says. Let there be one Lord.