Immediately after finishing his studies at the École Polytechnique, he was appointed "répétiteur" (teaching assistant) there, a position which he had occupied as an amateur while still a pupil in the school; for his schoolmates had made a custom of visiting him in his room after an unusually difficult lecture to hear him repeat and explain it. He was made deputy professor ("professeur suppléant") in 1802, and, in 1806 full professor succeeding Jean Baptiste Joseph Fourier, whom Napoleon had sent to Grenoble. In 1808 he became astronomer to the Bureau des Longitudes; and when the was instituted in 1809 he was appointed a professor of rational mechanics ("professeur de mécanique rationelle"). He went on to become a member of the Institute in 1812, examiner at the military school ("École Militaire") at Saint-Cyr in 1815, graduation examiner at the École Polytechnique in 1816, councillor of the university in 1820, and geometer to the Bureau des Longitudes succeeding Pierre-Simon Laplace in 1827.