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of past times, but superior to ordinary conversation because the speakers presented only their best thoughts.

Besides the text-books of the school, he was fond of reading such books as treated of curious and rare knowledge, and he had a high esteem for eloquence and poetry as gifts of genius rather than fruits of study. Those who can give clear and forcible expression to their thoughts, he said, though they spoke in Bas Breton and had never learned rhetoric, could always exercise the most persuasive power; and those who have the most pleasant fancies, and can express them most gracefully and with pertinent illustration, will not fail to be the best poets, though they have never studied the poetic art.

As the breadth of his knowledge enlarged, he grew more disposed to estimate the value of what he studied by its capacity of being made useful in life. He perceived the deficiencies of the logic and morals and of the physics and metaphysics that were taught in the college, and gained an increasing appreciation of the merits and beauty of the mathematical sciences. One of his first steps after leaving the college, he informs us in his Discourse on Method, was to discard his books, with all that he had learned that was uncertain, and to admit thenceforth only what seemed to have been demonstrated by reason and experiment. He therefore framed the method of examination and doubt, which, although he failed in very many instances to be true to it, has since become the great principle of positive science. He did not, however, he says, "imitate the skeptics, who doubt only for doubling's sake, and pretend to be always undecided; on the contrary, my whole intention was to arrive at certainty, and to dig away the drift and the sand until I reached the rock or the clay beneath."

After leaving the college, at the age of sixteen, he returned to his father, and in the next year went to Paris to participate in the social life of the capital and continue his studies. He renewed his school-day friendship with Marin Mersenne, now become Père Mersenne, of the Minim Friars, forming what proved to be a lasting alliance, and became associated with Claude Mydorge, one of the foremost mathematicians of France. Giving up the social side of his life, he withdrew for retirement and study to a secluded quarter. There is reason to believe that he made at this time some of his important geometrical studies, but he was not ready to publish them. A military career afforded at this age the most feasible means of getting the broadest views of life, and Descartes, in May, 1617, when twenty-one years of age, set out for the Netherlands and entered the service of Prince Maurice of Orange. Two years later he joined the forces of the Duke of Bavaria in the war between the house of Austria and the Protes-