Fourier, (Jean Baptiste) Joseph, Baron[fooryay]
Mathematician, born in Auxerre, C France. He accompanied Napoleon to Egypt (1798), and on his return (1802) was made prefect of the department of Grenoble, and created baron (1808). He then took up his first interest, applied mathematics, and while working on the flow of heat discovered the equation for it which now bears his name. To solve it, he showed that many functions of a single variable can be expanded in a series of sines of multiples of the variable (the Fourier series).