Du Châtelet, Gabrielle Emilie Le Tonnelier de Breteuil, marquise, 1706-1749

Gabrielle Émilie Le Tonnelier de Breteuil, Marquise du Châtelet (French pronunciation: [emili dy ʃɑtlɛ] ⓘ; 17 December 1706 – 10 September 1749) was a French natural philosopher and mathematician from the early 1730s until her death due to complications during childbirth in 1749.

Her most recognized achievement is her translation of and commentary on Isaac Newton's 1687 book Philosophiæ Naturalis Principia Mathematica containing basic laws of physics. The translation, published posthumously in 1756, is still considered the standard French translation.

Her commentary includes a contribution to Newtonian mechanics—the postulate of an additional conservation law for total energy, of which kinetic energy of motion is one element. This led her to conceptualize energy, and to derive its quantitative relationships to the mass and velocity of an object.

Her philosophical magnum opus, Institutions de Physique (Paris, 1740, first edition; Foundations of Physics), circulated widely, generated heated debates, and was republished and translated into several other languages within two years of its original publication.

She participated in the famous vis viva debate, concerning the best way to measure the force of a body and the best means of thinking about conservation principles. Posthumously, her ideas were heavily represented in the most famous text of the French Enlightenment, the Encyclopédie of Denis Diderot and Jean le Rond d'Alembert, first published shortly after du Châtelet's death.

Numerous biographies, books and plays have been written about her life and work in the two centuries since her death. In the early 21st century, her life and ideas have generated renewed interest. Émilie du Châtelet was born on 17 December 1706 in Paris, Émilie du Châtelet was born on 17 December 1706 in Paris, On 12 June 1725, she married the Marquis Florent-Claude du Chastellet-Lomont.[9][note 1] Her marriage conferred the title of Marquise du Chastellet.[note 2] Like many marriages among the nobility, theirs was arranged. As a wedding gift, her husband was made governor of Semur-en-Auxois in Burgundy by his father; the recently married couple moved there at the end of September 1725. Du Châtelet was eighteen at the time, her husband thirty-four.

Children
Émilie du Châtelet and the Marquis Florent-Claude du Chastellet-Lomont had three children: Françoise-Gabrielle-Pauline (30 June 1726 – 1754, married in 1743 to Alfonso Carafa, Duca di Montenero), Louis Marie Florent (born 20 November 1727), and Victor-Esprit (born 11 April 1733).[10] Victor-Esprit died as an infant in late summer 1734, likely the last Sunday in August.[11] On 4 September 1749 Émilie du Châtelet gave birth to Stanislas-Adélaïde du Châtelet, daughter of Jean François de Saint-Lambert. She died as a toddler in Lunéville on 6 May 1751.[12] Du Châtelet may have met Voltaire in her childhood at one of her father's salons; Voltaire himself dates their meeting to 1729, when he returned from his exile in London. However, their friendship developed from May 1733 when she re-entered society after the birth of her third child.[6] Du Châtelet's relationship with Voltaire caused her to give up most of her social life to become more involved with her study in mathematics with the teacher of Pierre-Louis Moreau de Maupertuis. He introduced the ideas of Isaac Newton to her. Letters written by du Châtelet explain how she felt during the transition from Parisian socialite to rural scholar, from "one life to the next."[20]

Final pregnancy and death

The chateau of Lunéville
In May 1748, du Châtelet began an affair with the poet Jean François de Saint-Lambert and became pregnant.[21] In a letter to a friend, she confided her fears that she would not survive her pregnancy. On the night of 4 September 1749 she gave birth to a daughter, Stanislas-Adélaïde. Du Châtelet died on 10 September 1749 [22] at Château de Lunéville,[23] from a pulmonary embolism. She was 42. Her daughter died 20 months later.[24]