SUMMARY. — This paper argues that there was a strong empirical movement among natural philosophers in mid-seventeenth century France : Mersenne, Gassendi, Pascal and the young Académie des sciences bear witness to it. By examining the origins of the experiments Jacques Rohault uses in his Traité de physique, carefully matching Rohaulťs experiments with Descartes' texts, for example, the author maintains that cartesian science was empirically oriented, not the a priori, purely rationalist enterprise textbooks would have us believe. Philosophers' later preoccupation with Descartes' Méditations has produced a stereotype which is at odds with the historical reality.RÉSUMÉ. — Cet article tend à montrer qu'il y avait, au milieu du XVIIe siècle, u...