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Émilie du Châtelet, who hypothesized conservation of energy, established kinetic energy as distinct from momentum and proportional to (speed)², and combined Newton, Leibniz, and her own original ideas in "Institutions de Physique," was born #OTD in 1706.
Portrait: M.Q. de La Tour
Portrait: M.Q. de La Tour
Born Gabrielle Émilie le Tonnelier de Breteuil, part of the French aristocracy, she was fascinated by astronomy, math, and physics. Her mother found her interests inappropriate, but her father supported them. He invited many well-known scientists to their home.
After marrying (she became the Marquise Du Châtelet), she continued her education on her own. She invited prominent scientists like Maupertuis, Koenig, and the Bernoullis to her home (which had a huge library and a laboratory) where they would discuss science and mathematics.
Maupertuis, you may recall, originated the idea that became the Principle of Least Action. https://twitter.com/mcnees/status/1310584269626994688
In 1737 du Châtelet submitted "Dissertation sur la nature et la propagation du feu" for a contest held by the French Academy of Sciences. In it, she hypothesized different colors of light transmitted different amounts of heat, and guessed at the existence of infra-red radiation.
Then in 1738, she published "Eléments de la philosophie de Newton" in Journals des Savants, advocating for Newton and arguing against Cartesian ideas of gravity. This contributed to the decline of the latter, which at the time was still relatively popular in France.
Du Châtelet’s work on Newtonian ideas led to a book written with Voltaire: “Elements of Newton’s Philosophy.” Voltaire’s name appeared on the cover, but he was clear that it was her work as much as his. Their contemporaries knew that she was by far the superior mathematician.
In 1740, du Châtelet published "Institutions de physique." It was presented as a textbook for her 13 year old son, but was in fact a significant work of natural philosophy that synthesized ideas of Leibniz and Wolff to establish a metaphysical basis for the work of Newton.
In the book, du Châtelet develops Leibniz's idea of vis viva — what we now call kinetic energy. Using experimental ideas of Dutch natural philosopher Willem Jacob 's Gravesande, du Châtelet established that this quantity must be proportional to the *square* of an object's speed.
This led to an extended and very public argument with Jean-Jacques d'Ortous de Mairan, the Secretary of the French Academy of Sciences. In an essay, de Mairan had asserted that the quantity we now know as kinetic energy should be proportional to the product of mass and velocity.
The argument raged for a few years and took a great toll on du Châtelet. Her rebuttals were eventually published as "Réponse de Madame la Marquise du Châtelet."
Photo: D. Lockard, Chemical Heritage Foundation
Photo: D. Lockard, Chemical Heritage Foundation
In retrospect everyone agrees that the argument was a bit one-sided: de Mairan was simply outclassed by du Châtelet. But du Châtelet's mentors and colleagues had failed to publicly support her. She resented them for it, and felt isolated.
A few years later, around 1748, she began working on a French translation of Newton's Principia. While working on the translation she learned that she was pregnant with her fourth child.
At age 42, du Châtelet was concerned that the pregnancy might be dangerous. She began working around the clock on her Principia translation. The work was completed just before the birth of her child.
Less than a week after giving birth she passed away.
Du Châtelet's translation of Principia remained unpublished for around ten years. The full work finally saw print in 1759, when the first predicted return of Halley's comet led to a surge of interest in Newton's mechanics.
Voltaire contributed a preface, in which he said of her: "For a long time she moved in circles which did not know her worth and she paid no attention to such ignorance."
Émilie du Châtelet's translation of Newton's Principia contained a great deal of commentary, derivations, and supplementary material, and is still considered the definitive French translation of the work.
In a letter to Frederick of Prussia, who apparently did not like her at all, du Châtelet said:
