JEAN BAPTISTE JOSEPH FOURIER (1768-1830), French mathematician, was born at Auxerre, March 21, 1768. He was the son of a tailor, and was left an orphan in his eighth year ; but through the kindness of a friend, who observed in him the promise of superior abilities, admission was gained for him into the military school of his native town, which was then under the direction of the Benedictines of Saint-Maur. He soon distinguished himself as a student, and made rapid progress, delighting most of all, but not exclusively, in mathematics. It was his wish to enter the artillery or engineer corps, but failing in this, he was appointed professor of mathematics in the I school in which he had been a pupil. This post he held for about four years (1789-1794), and during this time he was frequently called to lecture on other subjects, rhetoric, philosophy, and history. On the institution of the normal school at Paris he was sent to teach in it, and was afterwards attached to the polytechnic school. Fourier was one of the savants who accompanied Bonaparte to Egypt in 1798; and during this expedition he was called to discharge important political duties in addition to his scientific ones.
He was for a time virtually governor of half Egypt, was for three years secretary of the institute of Cairo, and undertook to deliver the funeral orations for Kléber and Desaix. On his return to France he was nominated prefect of Grenoble, and was created baron and chevalier of the Legion of Honour. He took an important part in the preparation of the famous Description de l'Egypte, and wrote the historical introduction. He held his prefecture for 14 years; and it was during this period that he carried on his elaborate and fruitful investigations on the propagation of heat in solid bodies. His first memoir on the mathematical theory of heat was crowned by the Academy. On the return of Napoleon I. from Elba in 1815, Fourier published a royalist proclamation, and left Grenoble as Napoleon entered it. He was then deprived of his prefecture, and, although immediately named prefect of the Rhône, was soon after again deprived. He now settled at Paris, was elected to the Academy of Sciences in 1816, but in consequence of the opposition of Louis XVIII. was not admitted till the following year, and was afterwards made perpetual secretary in conjunction with Cuvier. In 1822 he published his most celebrated work, entitled La Théorie Analytique de la Chaleur, which by its new methods and great results made an epoch in the history of mathematical and physical science. Of this work M. Cousin said that the grandeur of its results was no more to be questioned than their certainty, and that in the opinion of scientific Europe the novelty of the analysis on which they rest is as evident as its completeness. In 1827 Fourier was received at the French Academy, and the same year succeeded Laplace as president of the council of the polytechnic school. In 1828 he became a member of the Government commission established for the encouragement of literature. He died at Paris, May 16, 1830. After his death appeared his remarkable work en-titled Analyse des équations déterminées, which was written in his youth and left unfinished. It was completed and edited by M. Navier in 1831. In addition to the works above mentioned, Fourier wrote many memoirs on scien-tific subjects, and éloges of distinguished men of science.