French mathematician and student of Laplace whose devotion to mathematics led him to make the statement that life was only good for two things: to do mathematics and to teach it (Boyer 1968, p. 569). Poisson extended the theory of physical mechanics to replace analytical mechanics, publishing Traité de mécanique (2 vols., 1811, 1833). This theory was based on the hypothesis of molecular and forces. He showed that a particle placed in the interior of two similarly oriented ellipsoidal shells (a homeoid ) experiences no force. He also applied mathematics to electricity and magnetism, formulating the extension of Laplace's equation known as poisson's equation. He noted that the potential must be constant on the surface of a conductor, and analytically found the charge density on two spherical conductors in terms of digamma functions. He also formulated the theory of bound surface current and volume magnetization.

In 1819, during the judging of Fresnel's paper on diffraction at the Paris Academy, Poisson argued that the consequence of Fresnel's theory was that the center of the shadow of a diffracting disk should be illuminated. This unexpected effect was subsequent observed, verifying Fresnel's theory. His is also known for his work on probability, including what have now come to be known as Poisson Distributions. He derived what is now known as the weak law of large numbers. His work on probability was published in Recherches sur la probabilité des jugements (1837).

Additional biographies: MacTutor (St. Andrews), Bonn