LOUIS

See also:

• LOUIS POINSOT (1777–1859)

POINSOT (1777–1859)  , French mathematician, was born at Paris on the 3rd of January 1777 . In 1794 he became a scholar at the Ecole Polytechnique, which he left in 1796 to act as a civil engineer . In 1804 he was appointed professor of mathematics at the Lycee, in 1809 professor of analysis and mechanics, and in 1816 examiner at the Ecole Polytechnique: On the death of J . L . Lagrange, in 1813, Poinsot was elected to his place in the Academie des Sciences; and in 184o he became a member of the superior council of public instruction . In 1846 he was made an officer of the Legion of Honour; and on the formation of the senate in 1852 he was chosen a member of that body . He died at Paris on the 5th of December 1859 . Poinsot's earliest work was his Elemens de statique (1803; 9th edition, 1848), in which he introduces the idea of statical couples and investigates their properties . In the Theorie nouvelle de la rotation des corps (1834) he treats the motion of a rigid body geometrically, and shows that the most general motion of such a body can be represented at any instant by a rotation about an axis combined with a translation parallel to this axis,and that any motion of a body of which one point is fixed may be produced by the rolling of a cone fixed in the body on a cone fixed in space . The previous treatment of the motion of a rigid body had in every case been purely analytical, and so gave no aid to the formation of a mental picture of the body's motion; and the great value of this work lies in the fact that, as Poinsot himself says in the introduction, it enables us to represent to ourselves the motion of a rigid body as clearly as that of a moving point . In addition to publishing a number of works on geometrical and mechanical subjects, Poinsot also contributed a number of papers on pure and applied mathematics to Lionville's Journal and other scientific periodicals . See J .

L . F .

Bertrand, Discours aux funerailles de Poinsot (Paris, 1860) .