  Pascal's initial encounter with Jansenism had occurred when he was twenty-two years old. His father slipped on ice and dislocated or broke his thigh in January 1646. Following the accident, the Deschamps brothers, who had bone-setting and nursing skills, came to live in the Pascal household at Rouen for three months. They introduced the family to the strict observance of Christianity inspired by the Dutch theologian, Cornelius Jansen (1585–1638), and the French theologian, Jean Duvergier de Hauranne, who is more commonly known as the Abbé de Saint-Cyran (1581–1643). The evangelical work of the Deschamps brothers relied partly on Jansen's short treatise, the Discours sur la réformation le l'homme intérieur, which was based on the text of I John 2:16: “For all that is in the world is the concupiscence of the flesh and the concupiscence of the eyes and the pride of life, which is not of the Father but is of this world.” Jansen taught that a desire for knowledge was one form of concupiscence, and he argued that from this “illness … arises the investigation of nature's secrets (which are irrelevant to us), knowledge of which is useless, and which men do not wish to know except for the sake of knowing them” (Jansen 2004: 24). Jansen recommended that Christians should turn aside from the pride and concupiscence of human knowledge and scientific investigations, and that they should concentrate exclusively on knowledge of God. While this encounter with Jansenist theology is sometimes described as Pascal's first conversion, it is unlikely that he had already made the definitive choice about the insignificance of mathematical and scientific work that characterised his change of heart in the 1650s. He returned to Paris with his sister, Jacqueline, in 1647. Descartes met him there, in September 1647, during an extended trip to Paris from his usual residence in the north of Holland, and discussed with Pascal the results they might expect if they conducted the kind of experiment that was subsequently performed on the puy-de-Dôme.