Poisson - Poason (English spelling) Siméon-Denis Poisson

French mathematician and physicist. Born in Pithivier, he studied at the Ecole Polytechnique. During his time at the university, his talent was recognized by Lagrange and Laplace, and after graduation he became acting professor at his alma mater, and in 1806 he became professor as the successor to Fourier. In 1809, he became professor at the newly established Faculty of Sciences of the University of Paris. He made achievements in a wide range of fields, from mathematics to applied mathematics, and studied the theory of definite integrals and differential equations, introducing the concept of potential (1813), in which the "Poisson equation" is well known. He also made great contributions to probability theory, known for the calculus of variations, Fourier series, and the "Poisson distribution." He also studied thermology, capillary phenomena, electromagnetic field theory, and gravitation theory in terms of the application of mathematics to physics, and introduced the "Poisson ratio" in experiments on elasticity. He was a member of the Academy, and later served as a senator. He is the author of over 300 books and papers, including his major work, Traité de mécanique (1811).

[Jun Fujimura]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

フランスの数学者、物理学者。ピティビエに生まれ、理工科大学校（エコール・ポリテクニク）に学んだ。在学中、ラグランジュ、ラプラスらに才能を認められ、卒業後、母校の代理教授となり、1806年にはフーリエの後任として教授に就任。1809年、新設のパリ大学理学部教授となった。数学、応用数学の広い分野にわたって業績があり、定積分・微分方程式論を研究し、ポテンシャル概念を導入（1813）したが、これと関連して「ポアソン方程式」はよく知られている。そのほか変分法やフーリエ級数、「ポアソン分布」などで知られる確率論に大きな業績をあげた。数学の物理学への応用面での熱学、毛管現象、電磁場論、引力論などの研究もあり、弾性の実験では「ポアソン比」を導入している。アカデミー会員で、のち上院議員も務めた。主著『力学概説』Traité de mécanique（1811）をはじめ、300以上の著書、論文がある。

［藤村　淳］

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