But as soon as we come to the Physics of Aristotle we see at once his weakness. The knowledge of his age does not furnish him facts enough whereon to build, and the consequence is that he is forced into speculation. It will be sufficient for our purpose to allude to a few of his statements, either in this or in his metaphysical branch, to show how great is his uncertainty and confusion. Thus he asserts that matter contains a triple form--simple substance, higher substance, which is eternal, and absolute substance, or God himself; that the universe is immutable and eternal, and, though in relation with the vicissitudes of the world, it is unaffected thereby; that the primitive force which gives rise to all the motions and changes we see is Nature; it also gives rise to Rest; that the world is a living being, having a soul; that, since every thing is for some particular end, the soul of man is the end of his body; that Motion is the condition of all nature; that the world has a definite boundary and a limited magnitude; that Space is the immovable vessel in which whatever is may be moved; that Space, as a whole, is without motion, though its parts may move; that it is not to be conceived of as without contents; that it is impossible for a vacuum to exist, and hence there is not beyond and surrounding the world a void which contains the world; that there could be no such thing as Time unless there is a soul, for time being the number of motion, number is impossible except there be one who numbers; that, perpetual motion in a finite right line being impossible, but in a curvilinear path possible, the world, which is limited and ever in motion, must be of a spherical form; that the earth is its central part, the heavens the circumferential: hence the heaven is nearest to the prime cause of motion; that the orderly, continuous, and unceasing movement of the celestial bodies implies an unmoved mover, for the unchangeable alone can give birth to uniform motion; that unmoved existence is God; that the stars are passionless beings, having attained the end of existence, and worthy above other things of human adoration; that the fixed stars are in the outermost heaven, and the sun, moon, and planets beneath: the former receive their motion from the prime moving cause, but the planets are disturbed by the stars; that there are five elements--earth, air, fire, water, and ether; that the earth is in the centre of the world, since earthy matter settles uniformly round a central point; that fire seeks the circumferential region, and intermediately water floats upon the earth, and air upon water; that the elements are transmutable into one another, and hence many intervening substances arise; that each sphere is in interconnection with the others; the earth is agitated and disturbed by the sea, the sea by the winds, which are movements of the air, the air by the sun, moon, and planets. Each inferior sphere is