 When Descartes was at La Flèche, there already were signs that the conception of the universe was changing. Recall that Galileo's discovery of four moons of the planet Jupiter was celebrated at La Flèche in 1610. More generally, Copernicus had, in the previous century, offered a forceful argument for believing that the sun, not the earth, is at the center of the solar system. Early in the seventeenth century, Johannes Kepler announced new results in optics, concerning the formation of images, the theory of lenses, and the fact that the retinal image plays a central role in vision. By the early 1630s, Descartes was aware (1:263) of  William Harvey's claim that the blood circulates in the body.