Joseph-Louis Lagrange

(1736 – 1813)

Joseph-Louis Lagrange was born Giuseppe Lodovico Lagrangia in Turin, Italy, on January 25, 1736, the son of Giuseppe Francesco Lodovico Lagrangia and Teresa Grosso. Lagrange’s paternal great-grandfather was of French descent, but had settled in Italy, married a Roman, and adopted an Italian spelling of his surname. Lagrange gradually reverted to the original French, by which he is known today.

Lagrange was the youngest of eleven children, and the only one to survive his infancy. His family was originally quite prosperous, but his father squandered their money on ill-advised financial speculations. This proved fortunate, since Lagrange later admitted that had he been wealthy, he would not have chosen to pursue a career in mathematics.

When Lagrange was seventeen years old, his interest in mathematics was piqued by an article appearing in the Philosophical Transactions of the Royal Society of London. That essay, written by the British astronomer Edmund Halley, so fascinated Lagrange that he resolved to devote himself to the study of mathematics. That he was successful in this endeavor is evidenced by the fact that two years later, at the age of nineteen, he was appointed professor of mathematics at the Royal Artillery School in Turin.

It was at about this time that Lagrange initiated a longstanding correspondence with the formidable Leonhard Euler, then at the Academy of Science in Berlin. In his letter, Lagrange described his discovery of principles that would come to be known as the calculus of variations. Euler had already arrived at many of the same conclusions as those detailed by Lagrange, but recognized that Lagrange’s methods were superior to his. Euler graciously—and uncharacteristically—delayed publication of his existing manuscript. Euler thus gave the nineteen-year-old Italian the right to claim himself the founder of this new branch of analysis. Lagrange was immediately elevated to preeminence when news of the calculus of variations reached the European scientific community.

In 1766, when Euler left Berlin for St. Petersburg, King Frederick II of Germany eagerly assented to Euler’s suggestion that Lagrange be named Euler’s successor as head of the Berlin Academy. In issuing his invitation to Lagrange, Frederick noted, “It is necessary that the greatest geometer of Europe should live near the greatest of kings.” Lagrange concurred, and spent the next twenty years in Berlin in Frederick’s service.

In September 1767, soon after his arrival in Berlin, Lagrange married a distant cousin, Vittoria Conti. Unfortunately, Vittoria’s health declined soon thereafter, and she remained an invalid until her death in 1783.

While in Berlin, Lagrange immersed himself in the problems of astronomy and number theory, supervised the Academy’s mathematical program, and prepared monthly memoirs describing his mathematical discoveries. It was during this period, too, that Lagrange began to write his masterpiece, Mécanique analytique, which would be published in Paris in 1788. Mécanique analytique, or Analytical Mechanics, employed algebra and the calculus of variations to produce general equations from which to solve all problems in mechanics.

The death of his protector Frederick II in August 1786 placed Lagrange in a rather precarious position, so the French King Louis XVI’s suggestion that he join the Academy of Sciences in Paris was fortuitous. Though he was warmly welcomed and well compensated by the French, Lagrange unaccountably fell victim to a deep depression. He convinced himself that the study of mathematics was obsolete, and turned instead to the pursuit of botany and religion.

Lagrange was lifted from his lethargy in 1789 by the violent French Revolution, but his love of mathematics was rekindled by an extraordinary romance with the bright young daughter of his colleague, the astronomer Pierre Charles Le Monnier. Renée Françoise Adélaîde Le Monnier fell in love with Lagrange and was quite persistent in her advances. Lagrange, appalled by the forty-year difference in their ages, was at first reluctant to involve himself in a relationship with her, but in 1792 they were married. His wife’s devotion and support restored his emotional stability, and gave him great happiness.

Lagrange’s most important contribution to mathematics while in Paris was his leadership of the committee that devised the metric system. This invention standardized the previously chaotic French method of expressing weights and measures, and facilitated commerce. The metric system is today in universal use among scientists, who appreciate the remarkable logic of its construction.

Lagrange died in Paris on April 10, 1813, at the age of seventy-seven, and was buried with the honor befitting a man of his stature.

Links

http://www-history.mcs.st-andrews.ac.uk/Biographies/Lagrange.html
http://www.maths.tcd.ie/pub/HistMath/People/Lagrange/RouseBall/RB_Lagrange.html

References

• Asimov, Isaac. Asimov’s Biographical Encyclopedia of Science and Technology. Garden City, New York: Doubleday & Company, Inc., 1972.
• Ball, W. W. Rouse. A Short Account of the History of Mathematics. 1908. Reprint. New York: Dover Publications, Inc., 1960.
• Boyer, Carl B. A History of Mathematics. 2d ed., rev. Uta C. Merzbach. New York: John Wiley & Sons, Inc., 1991.
• Gillispie, Charles Coulston, ed. Dictionary of Scientific Biography. Vol. VII. New York: Charles Scribner’s Sons, 1973.
• Hooper, Alfred. Makers of Mathematics. New York: Random House, Inc., 1948.
• Simmons, George F. Calculus Gems: Brief Lives and Memorable Mathematics. New York: McGraw-Hill, Inc., 1992.
• Struik, Dirk J. A Concise History of Mathematics. New York: Dover Publications, Inc., 1987