834 THE POPULAR SCIENCE MONTHLY, 



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 dis- 

 posed 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 there- 

 fore framed the method of examination and doubt, which, al- 

 though he failed in very many instances to be true to it, has since 

 become the great principle of positive science. He did not, how- 

 ever, he says, " imitate the skeptics, who doubt only for doubl- 

 ing'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 Pere 

 Mersenne, of the Minim Friars, forming what proved to be a last- 

 ing 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 Des- 

 cartes, 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- 



