Baron Siméon Denis Poisson (, US also ; French: [si.me.ɔ̃ də.ni pwa.sɔ̃]; 21 June 1781 – 25 April 1840) was a French mathematician and physicist who worked on statistics, complex analysis, partial differential equations, the calculus of variations, analytical mechanics, electricity and magnetism, thermodynamics, elasticity, and fluid mechanics. Moreover, he predicted the Arago spot in his attempt to disprove the wave theory of Augustin-Jean Fresnel.
While his interpretations of physical phenomena were often proven wrong by later researchers, his contributions to mathematics have stood the test of time. He demonstrated that physical problems could suggest new mathematical ideas.
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