first nine months of his residence. He wrote from Amsterdam to Balzac, who had expostulated with him for having withdrawn himself from the world: "In this great city where I am, there being no one except myself who is not in trade, every one is so intent on his specnlations that I might stay here all my life without being seen by any one. I walk out every day amid the confusion of a great people with as much freedom and peace as you could have in your garden walks, and I pay no more attention to the men who pass before my eyes than you would to the trees in your woods and the animals feeding there. Even the noise they make works no more interruption to my thoughts than would the rumbling of a brook." He resumed his studies in dioptrics. Observations on parhelia gave the origin to his treatise on Meteors. He entered with great ardor upon the study of medicine and anatomy, and visited the butchers' shops every day to witness the slaughter of animals, of which he brought parts home to his rooms to be dissected at his leisure. His correspondence with Pere Mersenne abounded in mathematical problems which the two exchanged with each other. He studied astronomy and composed his Traite' du Monde, in which he avowed the doctrine of the motion of the earth. On learning, however, of the condemnation of Galileo, he suppressed this book, saying, in a letter to Père Mersenne: "All the things I have explained, although I believe them to be supported by very certain and very evident demonstrations, I would not for the world maintain against the authority of the Church. . . . My desire to live in quiet and continue the retired life I have begun makes me more content to see myself delivered from the fear of having gained more fame than I wished for by my writing, than sorry for having lost the time and trouble that I have taken in composing it."
Descartes made three visits to France during his residence in Holland. The first was in 1644, to settle family affairs after the death of his father in 1640; the second was signalized by an award to him of a pension secured by Cardinal Mazarin of three thousand francs, in consideration of the advantages which his investigations had conferred upon mankind, and to aid him in continuing them; the third visit ended in disappointment, for the substantial results anticipated from it were nullified by the breaking out of the civil war of the Fronde. During the second of these visits he is said to have met Pascal, and suggested to him the thought of experimenting on the weight of the air. A visit was made to England for the investigation of magnetic phenomena, and in 1634 Descartes took an excursion into Denmark.
A controversy in 1638 with Fermat concerning that author's book on Maxima and Minima, and on tangents, engaged the friends of both parties, and resulted in a friendship between the