For ten centuries the Greeks marched at the head of humanity, while Athens remained the centre to which the winds and the waves bore germs of civilization from the East, and whence, by the same instrumentalities, the seeds of yet richer harvests were scattered toward a more distant West. Hesiod, in his Works and Days, gave many practical lessons on agriculture, and more prosaic, but not less useful proficients arose on every hand to impart the most valuable instruction to each aspirant. The last effort of Grecian science was to mingle and combine in one system, all that the nations of the earth up to that era had produced. Diversified ideas of every shape and degree of worth were gathered around the torch of intense national enthusiasm, were made to comprehend and modify one another, and, in their sublimated union, gave birth to the first cultivated world. Plato was nearly cotemporary with Phidias, and, considering the great influence of his philosophic theory concerning the power of the soul to mold the outward person into its own pattern of virtue or vice, we can little doubt that the artist in his studio was greatly influenced by the sage of the Academy, both as to the choice of subjects and mode of treating them. But when the age of consummate art had passed, the Greeks perfected another great legacy to their successors, by making the last generation of her national industry the successful devotees of science. When every other department of literature and art in Athens were at their greatest splendor, the mathematics also flourished most; the former soon began to decline, but the sciences continued in power long after beauty in art had been eclipsed. Aristotle wrote nine books on animals. He may be fixed upon as representing the highest stage of knowledge and system the Greeks ever attained. Athenæus states, that Alexander gave him large sums of money, and several thousands of men, to hunt, fish, and otherwise aid in furnishing a vast collection in natural history, under the supervision of the philosopher. He was not only the first, but the only one of the ancients, who treated of separate species in the animal kingdom. But, although his system of physics accumulated numerous facts, Aristotle deduced not one general law to explain them. He knew the property of the lever as well, and many other correlative truths, but there was no correct theory of mechanical powers in the world, before Archimedes struck upon a generic principle of science. Before him, no one had arranged the facts of space, body, and motion, under the idea of mechanical cause, which is force.