Joseph Louis de Lagrange was born on January 25, 1736 in Turin and died on April 10, 1813 in Paris. He spent his first years in Turin, his maturity in Berlin, and his last years in Paris, where he achieved his greatest fame. Like Newton, but at an even younger age, he came to mathematical knowledge in an incredibly short time.

At sixteen years of age he was appointed professor of mathematics at the Royal School of Artillery in Turin. His charming personality attracted his friendship and enthusiasm. Soon he led a young group of scientists, who were the first members of the Turin Academy.

At nineteen years of age, he gained fame by solving the so-called isoperimetric problem, which had baffled mathematicians for half a century. He also invented a new method for calculating variations, which would be the central theme of his life's work. The principle led to the even more fruitful results of Hamilton and Maxwell and, subsequently, continued in Einstein's work and in the last phases of wave mechanics.

After several years of the greatest intellectual effort, he succeeded Euler as director of the Berlin Academy of Sciences. Occasionally he was seriously ill, due to overwork. In Germany, King Frederick, who had always admired him, soon began to like his modest manners, and rebuked him for his intemperance in the study, which threatened to unhinge his mind. He continued to reside in Prussia for twenty years, producing works of high distinction, which culminated in his Mécanique Analytique, which was published in France.

In 1787 he moved to Paris. The mathematicians flocked to receive him and to pay him all the honors, but they were discouraged to find that his talent for mathematics had disappeared. The years of activity produced their effect, and Lagrange was mathematically worn. For two years, he never opened his Mécanique Analytique; on the contrary, he directed his thoughts to any other point, to metaphysics, history, religion, medicine, etc. Lagrange continued for two years in this philosophical and non-mathematical state, when suddenly the country was precipitated to the Revolution. In later years, his mathematical ability returned again, and he produced many gems of algebra and analysis.

Lagrange conducted dynamics studies of the Solar System bodies, investigating in particular the movements of the Moon and Jupiter satellites. Among its astronomical discoveries, the so-called *ridding points of a celestial body*, known as the **Lagrange points**, which have important astronautic applications.

During the period of the French Revolution, he was in charge of the commission for the establishment of a new system of weights and measures, the Decimal Metric System. After the Revolution, he was professor of the new École Normale and with Napoleon he was a member of the Senate and received the title of count. He was one of the great mathematicians of the eighteenth century; He created the calculation of variations, systematized the field of differential equations and worked on number theory.

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