# Maupertuis, Pierre-Louis Moreau de

**Maupertuis, Pierre-Louis Moreau de** (1698-1759): French mathematician, philosopher, and man of letters. Maupertuis is credited with having invented the Principle of Least Action, which states that in all natural phenomena a quantity called “action” tends to be minimized.

Born in Saint-Malo, France, to a moderately wealthy merchant family, he is sent to study at the College de la Marche in Paris in 1714. After two years in Paris, he returns to Saint-Malo at the insistence of his mother and is educated in mathematics by a private tutor. After completing his formal education, he obtains the position of lieutenant in the Musketeers, and in 1718 he joins the regiment of La Roche Guyon. By 1722, he gives up his career as a cavalry officer and moves to Paris to begin to build his reputation as a mathematician. There he meets the dramatist, novelist, and journalist Marivaux, Pierre Carlet de Chamblain de and the playwright La Motte, as well as mathematicians Joseph Saurin, Nicole, and Terrasson. He is admitted to the Académie des Sciences in 1723 at the age of 25, and in the following year he publishes his first paper, “Sur la forme des instruments de musique,” which studies the effect of the shape of an instrument on the characteristics of the note produced. This paper is followed by others: on maxima and minima in 1726, on the cycloid in 1727, and others on curves in 1727, 1728, and 1729. He also shows a keen interest in biology during this period, when he acts as secretary to the naturalist Bignon and writes an important paper on the salamander. He visits London in 1728 and is elected a Fellow of the Royal Society.

He leaves for Basel to study under Johann Bernoulli in order to enhance his knowledge of math and science at the University of Basel. There he learns of Descartes’s vortex theory model of the solar system and of Leibniz’s views on mechanics. He also learns of Newton’s physics. He returns to Paris in July of 1730. By 1731, he writes his first paper on astronomy and another on differential equations, while at the same time developing his reputation. In 1732 he publishes a paper which treats rotating bodies that discusses the nature of Saturn’s rings and the shape that a rotating body assumes. It contains errors, showing that Maupertuis has not yet fully understood Newton’s inverse square law and the resulting gravitational force within a solid body. He declares himself a supporter of Newton’s theory of gravitation with his publication of *Figure des astres* in 1732. This treatise announces Mautpertuis’s position on the biggest problem of the period, that of the shape of the earth. In 1736, he acts as chief of the French Geodesic Mission, sent by King Louis XV to Lapland to measure the length of a degree along the meridian. His measurement verifies the Newtonian view that the earth is an oblate spheroid, flattened at the poles. The results of the measurements are made public in Maupertuis’s book *La Figure de la Terre* in 1738. Upon his return from the Lapland expedition, he sets about generalizing his earlier mathematical work.

In 1740, Maupertuis goes to Berlin on the invitation of the King of Prussia, and takes part in the Battle of Mollwitz, where he is taken prisoner by the Austrians. On his release, he returns to Paris in 1742 and is elected director of the Academy of Sciences. The following year, he is also elected to the Académie Française. In 1745 he returns to Berlin where he marries Eleonor Borck that same year. He is appointed president of the Berlin Academy in 1746 at the wish of Frederick II, the Great and holds this post for eight years. It is also in 1746 that he proposes his Principle of Least Action as a metaphysical principle that underlies all the laws of mechanics. He publishes it four years later in his *Essai de cosmologie*. When his health declines in 1757, he retires to the south of France, then leaves for Basel in 1758 where he dies a year later.

The Maupertuis Crater on the Moon is named after him.

Further Reading:

Mary Terrall, *The Man Who Flattened the Earth: Maupertuis and the Sciences in the Enlightenment*, 2002.

David Beeson, *Maupertuis: An Intellectual Biography*, 1992.

**Lisa F. Signori**

College of Charleston