Louis Poinsot

Louis Poinsot (3 January 1777 – 5 December 1859) was a French mathematician and physicist. Poinsot was the inventor of geometrical mechanics, showing how a system of forces acting on a rigid body could be resolved into a single force and a couple.

Louis was born in Paris on 3 January 1777. He attended the school of Lycée Louis-le-Grand for secondary preparatory education for entrance to the famous École Polytechnique. In October 1794, at age 17, he took the École Polytechnique entrance exam and failed the algebra section but was still accepted. A student there for two years, he left in 1797 to study at École des Ponts et Chaussées to become a civil engineer. Although now on course for the practical and secure professional study of civil engineering, he discovered his true passion, abstract mathematics.

Poinsot thus left the École des Ponts et Chaussées and civil engineering to become a mathematics teacher at the secondary school Lycée Bonaparte in Paris, from 1804 to 1809. From there he became inspector general of the Imperial University of France. He shared the post with another famous mathematician, Delambre. On 1 November 1809, Poinsot became assistant professor of analysis and mechanics at his old school the École Polytechnique. During this period of transitions between schools and work, Poinsot had remained active in research and published a number of works on geometry, mechanics and statics so that by 1809 he had an excellent reputation.

By 1812 Poinsot was no longer directly teaching at École Polytechnique using substitute teacher Reynaud, and later Cauchy, and lost his post in 1816 when they re-organized, but he did become admissions examiner and held that for another 10 years. He also worked at the famous Bureau des Longitudes from 1839 until his death. On the death of Joseph-Louis Lagrange in 1813, Poinsot was elected to fill his place at the Académie des Sciences. In 1840 he became a member of the superior council of public instruction. In 1846 he was awarded an Officer of the Legion of Honor, and on the formation of the Senate in 1852 he was chosen a member of that body. Poinsot was elected Fellow of the Royal Society of London in 1858. He died in Paris on 5 December 1859.

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