Aristotle's physics must necessarily have been very bad in detail. This was common to all philosophers until the time when the Galileos, the Torricellis, the Guerickes, the Drebels, and the Academy del Cimento began to make experiments. Natural philosophy is a mine which cannot be explored without instruments that were unknown to the ancients. They remained on the brink of the abyss, and reasoned upon without seeing its contents.
Aristotle's Treatise on Animals.
His researches relative to animals formed, on the contrary, the best book of antiquity, because here Aristotle made use of his eyes. Alexander furnished him with all the rare animals of Europe, Asia, and Africa. This was one fruit of his conquests. In this way that hero spent immense sums, which at this day would terrify all the guardians of the royal treasury, and which should immortalize Alexander's glory, of which we have already spoken.
At the present day a hero, when he has the misfortune to make war, can scarcely give any encouragement to the sciences; he must borrow money of a Jew, and consult other Jews in order to make the substance of his subjects flow into his coffer of the Danaides, whence it escapes through a thousand openings. Alexander sent to Aristotle elephants, rhinoceroses, tigers, lions, crocodiles, gazelles, eagles, ostriches, etc.; and we, when by chance a rare animal is brought to our fairs, go and admire it for sixpence, and it dies before we know anything about it.
Of the Eternal World.
Aristotle expressly maintains, in his book on heaven, chap, xi., that the world is eternal. This was the opinion of all antiquity, excepting the Epicureans. He admitted a God—a first mover—and defined Him to be "one, eternal, immovable, indivisible, without qualities."
He must, therefore, have regarded the world as emanating from God, as the light emanates from the sun, and is co-existent with it. About the celestial spheres he was as ignorant as all the rest of the philosophers. Copernicus was not yet come.
His Metaphysics.
God being the first mover, He gives motion to the soul. But what is God, and what is the soul, according to him? The soul is an entelechia. "It is," says he, "a principle and an act—a nourishing, feeling, and reasoning power." This can only mean that we have the faculties of nourishing ourselves, of feeling, and of reasoning. The Greeks no more knew what an entelechia was than do the South Sea islanders; nor have our doctors any more knowledge of what a soul is.
His Morals.