It was during his second residence in Athens, in the twelve years from B.C. 335 to 323, that Aristotle composed most of those great works in which he sought to sum up, in an encyclopædic way, the results of a life of all-embracing study and thought. He had been in no haste to put himself on record, and it was not until he had reached a consistent view of the world that he ventured to treat, in a definitive way, any aspect of it. Thus it was that each of his treatises formed part of one great whole of thought. Had he succeeded in completing his plan, he would have left to the world a body of science such as, even in our own day, would look in vain for a peer among the works of any one man. Unfortunately, his plan was not completed, and even of the works which he did write only a portion has come down to us. But that portion is sufficient to place their author at the head of all scientific men. Some of his works, for example, his _Logic_, _Metaphysics_, _Ethics_, and _Politics_, still occupy the first place in the literature of these subjects. How a single man could have done all that he did, and in so many different departments, is almost inconceivable. No doubt he had helpers, in the shape of secretaries, learned slaves, and disciples; and it is certain that he received from his royal pupil munificent aid, which enabled him to do much, especially in the directions of physical and political research, that would have been impossible for a poor man; but, after all allowances have been made, his achievement still seems almost miraculous.