Poisson, Simeon-Denis (1781-1840), French mathematical physicist. Born in Pithiviers, Loiret, he is best known for his theoretical contributions to electricity and magnetism, although he also published extensively on other topics, such as the calculus of variations, differential geometry, and probability theory. The Poisson distribution is a special case of the binomial distribution in statistics. At the Ecole Polytechnique he came under the influence of the mathematician Joseph Louis Lagrange, and in 1802 became the assistant of Jean-Baptiste Joseph Fourier, whose Chair he assumed in 1808. Later he became the first Professor of Mechanics at the Sorbonne and a leading member of the French scientific establishment. His seminal memoir on electricity appeared in 1812: in this he adopted, as Charles Coulomb had done before him, a two-fluid model of electricity: like fluids repelled, unlike attracted, according to the inverse-square law. A body became electrified either positively or negatively when the uniform distribution of both fluids was disturbed. By means of Lagrange's potential function he attempted to calculate mathematically the distribution of electric charges on the surfaces of conductors. Poisson demonstrated, in 1824, that these formulations were equally applicable to magnetism. He was unfairly charged by his contemporaries with lack of originality. He was also interested in the theory of elasticity; in astronomy he worked primarily on the mathematics of the motion of the Moon.

Contributed By:
Willem Dirk Hackmann