In this, Flaxman agrees, when he says: "It must not be supposed that those simple geometrical forms of body and limbs, in the divinities and heroes of antiquity, depended upon accidental choice, or blind and ignorant arbitration. They are, on the contrary, a consequence of the strict and extensive examination of nature, of rational inquiry into its most perfect organization and physical well-being, expressed in outward appearance." "That the Greeks," says Bossi, "wrote much on this subject [their doctrine respecting symmetry] we have ample evidence in Pliny, Vitruvius himself, Philostratus the younger, and others. "Polycletus did not confine himself to giving a commentary upon this fundamental point, but, in illustration of his treatise, according to Galen, made an admirable statue that confirmed the precepts laid down in the work; and 'The Rule of Polycletus,' the name given to this statue, became so famous for its beauty, that it passed into a proverb to express a perfect body, as we may find in Lucian. "But of so many writings, which ought at least to equal the works that remain to us, and probably were superior, inasmuch as it is easier to lay down precepts than to put them in execution--of so many treatises, I say, not a fragment remains [except the few lines of Vitruvius], nor is there, now, any hope that a vestige will be found, unless something may remain for posterity among the papyri of Herculaneum." Now, to approach to the ancients in excellence is quite impossible, until some one shall explain the great principles on which they acted. Assuredly they are, in some of the most important respects, unknown at present. Servile imitation will never answer the purpose; and to learn as the ancients did, and reach perfection, perhaps, in as many ages, is not very rational, when we can avail ourselves of their practice to discover their principles. I will, in this chapter, endeavor to point out some of these principles in the practice of art, as I have already done in the general theory of beauty. "It is probable," says Winckelmann, "that the Grecian artists, in imitation of the Egyptians, had fixed, by well-determined rules, not only the largest, but even the very smallest proportions, and the measure of the length proper to every age and to every kind of contour; and probably all these rules were learned by young persons, from books that treated of symmetry." These rules, we know, were of three kinds--numerical, geometrical, and harmonic; and we shall see, in the sequel, that the loss of them has been much deplored. It is not a little curious, however, that the numerical and geometrical methods are, in some measure, actually practised even at the present day, and that the harmonic method (the loss of which has caused the greatest confusion) is easily deducible from anatomical and physiological principles, as I shall endeavor to show.