Joseph Louis Lagrange. Portrait of the French mathematician Comte Joseph Louis Lagrange (1736- 1813). Lagrange became a professor at the Turin Royal Artillery School in Italy when he was 19. He later moved to Berlin, Germany and then to Paris, France. Although his major work, Analytical Mechanics, was started when he was 19, it was only finished when he was 52. In it he treated general mechanical problems using a powerful combination of two forms of calculus. He contributed to number and gravitational theory, and found solutions and proofs for various unsolved problems. He worked on weights and measures and the development of the metric system. Artwork from an 1833/37 book.