Gabrielle Émilie Le Tonnelier de Breteuil, Marquise du Châtelet-Laumont, 1706-1749. French Enlightenment translator of philosophical and scientific works, including Newton's Principia. She was a friend and correspondent of Voltaire. Her own thinking was strongly influenced by Leibniz, on whose physics her chief original book was based. She is a pivotal figure in the history of mathematics and of early modern philosophy.