GIOSEPPE LUIGI LAGRANGE. - Mathematician, b. in Turin on 25 Jan. 1736, d. in Paris on 10 Apr. 1813. His original name was Lagrange. A pupil of the Turin Military Artillery School, he was appointed as a teacher there in 1755. From that time began his scholarly output and activity, which led him to found a private society among the cultivators of science; this was later elevated to an Academy of Sciences and remains one of the most important Italian academies.
In the proceedings of the Society he published important works that earned him the esteem and protection of D’Alembert, through whom he shortly afterwards obtained the directorship of the Berlin Academy, where he remained for twenty years. In 1787 he moved to Paris.
He addressed fundamental analytical questions concerning: the theory of functions; the simplification of infinitesimal calculus; the solution of numerical equations by separating roots through the method of transforming the squares of the differences between the roots themselves; the calculation of functions by means of power series or by polynomials, with a synthetic expression of the approximation (remainder); integration of differential equations and solution of equations in finite differences; research on the periodic variations of planetary motion.
Lagrange was thus a great analyst, but also a great expositor. 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 Galileo, and that of lost forces, due to D’Alembert—he rigorously deduced all the equations of equilibrium and motion, making use also of the coordinates that bear his name, and through which the aforementioned equations assume a more synthetic form.