Louis Poinsot

Louis Poinsot (January 3rd 1777 with Clermont-in-Beauvaisis - December 5th 1859 with Paris) is a Mathématicien French (Academy of Science, 1813) known for its contributions to the Mechanic .

Years of training

Wire of a grocer of Beauvais, it made its classes of rhetoric to the Louis-the-Large Lycée in Paris (1789-1793). Raise shining in traditional literature, it presented itself to the first entrance examination to the Polytechnic school (then called central École of public works) and in spite of its ignorance of the algebra, was allowed (1794). Recruited at the school of application of the Bridges & Roadways (1797), it obtained there the price of mechanics for a project of saw with recéper the underwater piles, inspired of a similar invention of Louis Alexandre de Cessart.

The first research

From 1800 to 1803, Poinsot is affected in Paris without precise project: the Consulate lack of money and the chief engineer Pierre-Simon Girard try at this time to obtain a political decision for the drain of the Ourcq. In the interval, Poinsot is occupied with research on the resolution of the algebraic equations, and with a setting with clean of its notes of course on statics. The result of this last work is crowned success: the Éléments of statics (1803) from the start are greeted as a book with exceptional didactic qualities; they replace in technical education the Statique of Charles Bossut and will be republished eleven times (1811, 1821,1824,1830,1834,1837,1842,1848,1861,1873,1877) until the discipline itself, become a simple consequence of Dynamics, falls in disuse in teaching.

Years of success

Precise definitions, clearness of the reasoning, systematic reduction of the questions to geometrical methods reveal the style of Poinsot, which, this same year, gives up the career of engineer and is recruited as mathematics professor with the college Bonaparte. Recognized now by the Institute, it deposits a report (printed paper form then under the title of general Théorie of the balance and the movement of the systems ) criticizing the principle of virtual work. This principle, among the other possible ones, had been chosen by Joseph-Louis Lagrange to axiomatize statics in its Analytical mechanics (1788). Lagrange, which was then the senior and the supreme authority of the Institut, was moved by the temerity of the young author. However, after two surging interviews, it seems that Lagrange, in the absence of being convinced by the arguments of Poinsot, recognized rigor and courage to him: it obtained to him the load of inspector of the universities (1808).

Professorship with Positivism

To this station, Poinsot endeavoured to promote the teaching of sciences, then almost non-existent, in the universities and especially the colleges. In literature, it recommended to the professors to limit their courses to a small number of works chosen, while more emphasizing some the exemplary value. He encouraged the memorizing of the traditional texts particularly.

Taking again the observations of Adrien-Marie Legendre on the polyhedrons, it described two polyhedral regular spangled not yet examined, and showed by a combinative argument that there are of them no others (1809).

With died of Lagrange (1813), Poinsot was elected at the Institute in the class of mathematics; but to the Restoration, like other dignitaries of the imperial mode, it was relegated of its various stations, to start with the Polytechnic school. Its relations with Siméon Denis Poisson degrading himself, the general inspection was removed to him with the advent of Charles X (ordinance of September 22nd, 1824). Suspected of political Liberalism, its enthusiasm for the Système of Positive Policy of Auguste Count drew aside it still a little more of the capacity.

Work of mechanics

In its effort for géométriser mechanics, Poinsot highlighted the importance of the concept of moment, showing how to reduce to a Torseur a system of forces acting on a solid. In its new Theory of the rotation of the Bodies (1834), it shows that the movement of a solid breaks up into an instantaneous rotation around an axis and an instantaneous translation parallel with this axis; then that the movement of a solid around a fixed point (Mouvement in Poinsot), can be illustrated by the bearing of a cone interdependent of the solid, on a fixed cone. Its study on the movement of the cone generalizes that of Euler on the Toupie (cone in rotation around a fixed axis).

The Classicisme of Poinsot led it to then refute the mathematical theory of elasticity in full rise, because this one introduced, according to him without need, of the additional assumptions to the mechanics of the point and the rigid solids. Joseph Bertrand pays:

Curious about the theory of the solid bodies, it separated it entirely from that of the elastic bodies. Neither Navier, neither Poisson, neither Cauchy, nor Lamé, for which it always had a so high regard, succeeded in making him discuss their principles. “They speak about oblique pressures, said it with loathing, that is not pure, a pressure is always normal”, and moving away from its spirit this image and this importunate phrase, it rested at once its sight on the bodies abstractedly, i.e. absolutely rigid, and finished by geometrical surfaces of a so perfect polish, which one should not even speak. An imperfect polish, a rough surface, which do you hear by there, I request from you, as geometricians? ”

Poinsot thought that one could mathématiser the theory of the deformable bodies by considerations of resultant and couple between material points. Its ideas influenced the Cosserat brothers.

Back in favor

After the days of 1830, the vice is loosened around holding of the Positivisme and the liberals in general. Elected with the council of improvement of the Polytechnic school, astronomer to the Office of longitudes in 1839, Poinsot found the station of Advising Royal for the State education only at the beginning of Siméon Denis Poisson, in 1840. Criticized by Auguste Count for his insufficient support against the candidature of Charles Sturm for the Polytechnic school, it had to still redouble prudence when the father of the Positivisme was évincé of this establishment in 1845. Anxious to promote the teaching of mathematics in France, it made open in 1846 a pulpit of higher geometry than the Sorbonne, entrusted to Michel Chasles.

With the re-establishment of the Empire, it was named with the Sénat and was made Pair of France (1852).

Writings

Its work includes:

Elements of statics (1803)
Memory on the composition of the momens and the surfaces in Mechanics (1804)
Memory on the general theory of the balance and the movement of the systems (1806)
On the polygons and the polyhedrons (1809)
Theory and determination of the equator of the solar system (1828)
new Theory of the rotation of the bodies (1834)
Theory of the travelling circular cones (1853)

Homages

Its name is registered on the Eiffel Tower.

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