LAGRANGE, GIUSEPPE LUIGI. - Mathematician, b. in Turin on 25 Jan. 1736, d. in Paris on 10 Apr. 1813. His name was originally Lagrangia. A pupil of the military artillery school of Turin, he was appointed there as a teacher in 1755. From that time began his output and activity, which led him to found a private society among devotees of science, which was later established as the Academy of Sciences and is still one of the major Italian academies.
In the proceedings of the Society he published important works that won him the esteem and protection of D'Alembert, through whom, shortly afterward, he obtained the directorship of the Academy of Berlin, where he remained for twenty years. In 1787 he moved to Paris.
He dealt with fundamental analytical questions concerning: the theory of functions; the simplification of infinitesimal calculus; the solution of numerical equations by means of the separation of roots with the method of the transformation of the squares of the differences between the roots themselves; the calculation of functions by means of power series, or by means of polynomials, with a synthetic expression of the approximation (remainder); integration of differential equations and solution of finite-difference equations; research on the periodic variations of the motion of the planets.
L. was therefore a great analyst, but also a great treatise writer. In addition to the Traité de la résolution des équations numériques, he wrote the celebrated Mécanique analytique (Paris 1787), a monumental work in which, basing himself on two principles, that of virtual work, due to Galilei, and that of lost forces, due to D'Alembert, he rigorously deduced all the equations of equilibrium and motion, also making use of the coordinates that took their name from him, and through which the aforementioned equations assume a more synthetic form.
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