Fourier, Jean Baptiste Joseph, Baron, 1768-1830, French mathematician and physicist. He was noted for his researches on heat and on numerical equations. He originated Fourier's theorem on vibratory motion and the Fourier series, which provided a method for representing discontinuous functions by a trigonometric series. Fourier was professor (1795-98) at the École polytechnique, Paris; accompanied Napoleon I to Egypt; and was prefect of Isère (1802-15). In 1808 he was made a baron. He wrote Théorie analytique de la chaleur (1822; tr. 1878, repr. 1955). His scientific writings were collected in two volumes (1888-90).