Comte Joseph-Louis Lagrange

1736-1813

French-Italian Mathematician and Astronomer

Comte Joseph-Louis Lagrange ranks among the most important eighteenth-century Continental mathematicians. His best-known feat is the establishment of the metric standard, but this accomplishment came only after a number of other achievements, including contributions to algebra and number theory. Lagrange paved the way for modern mechanics by helping to establish a link between solid and fluid forms and he invented the calculus of variations when he was just 19 years old.

Born in Turin, Italy, on January 25, 1736, Lagrange was the son of aristocrats. His father served as treasurer of war in Sardinia and his mother came from a wealthy Italian family. Although Joseph-Louis was their eleventh and last child, he was the only one to survive childhood.

Initially, Lagrange showed little interest in mathematics, but, after reading an essay on calculus by Sir Edmond Halley (1656-1742), the course of his life was set. At age 16, the boy genius was sufficiently knowledgeable on the subject of calculus to serve as professor of mathematics at the artillery school in Turin. Three years later, while working on a set of isoperimetric problems then very much under discussion by the leading mathematicians of Europe, Lagrange developed the calculus of variations. After he sent a letter describing his work to Leonhard Euler (1707-1783) in Berlin, the two struck up a correspondence. Euler, nearly 30 years his senior, helped arrange Lagrange's election to the Berlin Academy.

Lagrange continued to make great strides in mathematics throughout the 1750s and 1760s. In 1759 he contributed three papers to a book published by the Turin Academy of Sciences and in the last of these papers used a partial differential equation as a means of providing a mathematical description of string vibrations. With this paper, he helped settle a controversy of long standing between Euler and Jean Le Rond d'Alembert (1717-1783). In 1764 the French Académie Royale des Sciences sponsored a contest to determine the gravitational forces that cause the Moon to present a relatively consistent face to Earth. Lagrange won the grand prize and another one two years later in a contest regarding the planet Jupiter.

The second académie prize was but one of many significant events for Lagrange in 1766, the year in which he married and also took the position, recently vacated by Euler, of director of mathematics at the Berlin Academy. A year later, Lagrange published On the Solution of Numerical Equations, in which he discussed universal methods for reducing equations from higher to lower degrees, thus preparing the way for modern developments in algebra. He proved several of Fermat's theorems, thereby contributing to number theory in its nascent stages, and in 1772 won his third académie grand prize for a study of the gravitational forces involving Earth, the Sun, and the Moon. Two more grand prizes followed, in 1774 and 1778.

During the 1780s, even as his Mécanique Analytique (1788) revolutionized the understanding of mechanics, Lagrange was mired in a period of depression. He had earlier lost his wife to an illness and remained widowed for many years. In 1792, at the age of 56, he again married, this time to the teenaged daughter of a friend, the astronomer Pierre-Charles Lemonnier. Neither of his marriages produced children.

The French Revolution, which began in 1789, seemed to shake Lagrange out of the period of malaise that had begun nearly a decade before. By then, he had long since moved to Paris. During the revolution, Lagrange was appointed to a committee for establishing standards of weights and measures; at this period, he developed the metric system.

A second fruitful period of Lagrange's life extended from the time of his second marriage to his death 21 years later. During this time, he wrote extensively and maintained professorships first at the Ecole Normale and later the Ecole Polytechnique. Lagrange died on April 10, 1813.

JUDSON KNIGHT