Mining engineer, one of the greatest mathematicians of all time. He is interested in the works of Hermite, discovers in 1881 the automorphic functions (fuchsian and kleinian), publishes a report "On the three body problem and the equations of dynamics" (1889) which offers a new way to theoretical celestial mechanics. He devotes his latest writings to the philosophy of science. Member of the Institute (Académie des sciences (1887), Académie française (1908). In 1904 was appointed professor of general astronomy to replace Callandreau at the Ecole polytechnique