Émilie du Châtelet's most recognized achievement is her philosophical magnum opus, Institutions de Physique (Paris, 1740, first edition; Foundations of Physics). She then revised the text substantially for a second edition with the slightly modified title Institutions physiques (Paris, 1742). It circulated widely, generated heated debates, and was translated into German and Italian in 1743. The Institutions covers a wide range of topics, including the principles of knowledge, the existence of God, hypotheses, space, time, matter and the forces of nature. Several chapters treat Newton's theory of universal gravity and associated phenomena. Later in life, she translated into French, and wrote an extensive commentary on, Isaac Newton's Philosophiæ Naturalis Principia Mathematica. The text, published posthumously in 1756, is still considered the standard French translation to this day.
Education
Émilie du Châtelet's father, Louis Nicolas le Tonnelier de Breteuil, arranged for Bernard Le Bovier de Fontenelle, the permanent secretary of the French Académie des Sciences, to discuss astronomy with her when she was ten. Accounts differ about the role of her mother, Gabrielle Anne de Froulay, in her education. Some sources state that she opposed her daughter's intellectual interests, while others indicate that she encouraged du Châtelet to question accepted claims.
Her father arranged training in fencing and riding and later brought tutors to the family home. By the age of twelve, she was fluent in Latin, Italian, Greek and German, and she later translated Greek and Latin plays and philosophy into French. She also studied mathematics, literature and science. Du Châtelet danced, played the harpsichord, sang opera and acted. As a teenager, she used mathematical strategies in gambling when she needed money to buy books.
In 1733, aged 26, du Châtelet resumed her mathematical studies. She initially studied algebra and calculus with Pierre Louis Moreau de Maupertuis, a French mathematician and member of the Académie des Sciences. By 1735, she was studying with Alexis Clairaut, a French mathematician known for Clairaut's equation and Clairaut's theorem.
Translation and commentary on Newton's Principia
In 1749, the year of du Châtelet's death, she completed the work regarded as her outstanding achievement: her translation into French, with her commentary, of Newton's Philosophiae Naturalis Principia Mathematica (often referred to as simply the Principia), including her derivation of the notion of conservation of energy from its principles of mechanics. Despite modern misconceptions, Newton's work on his Principia was not perfect. Du Châtelet took on the task of not only translating his work from Latin to French, but adding important information to it as well. Her commentary was as essential to her contemporaries as her spreading of Newton's ideas. Du Châtelet's commentary was very extensive, comprising almost two-thirds of volume II of her edition.
To undertake this project, du Châtelet prepared to translate the Principia by continuing her studies in analytic geometry, mastering calculus, and reading works in experimental physics. Her preparation afforded her commentary information derived from her own research as well as from the work of other scientists she studied or worked alongside. This helped du Châtelet with her commentary on the Principia and its translation and in writing her other works such as the Institutions de Physique.
Advocacy of kinetic energy
Du Châtelet participated in the debate over vis viva, a quantity associated with the motion of bodies. Drawing on Leibniz’s ideas, she publicized experiments by Willem ’s Gravesande in which balls dropped into soft clay left indentations of different depths. The experiments supported relating the effect of motion to the square of velocity. These arguments belonged to an eighteenth-century dispute whose terminology did not yet match the later, fully developed distinction between momentum and energy.
Her discussion helped connect philosophical arguments about motion with measurable physical effects. Du Châtelet treated translation, mathematical study, and experimental evidence as complementary activities. The commentary accompanying her French Principia drew on her own learning and on work by other scientists. Its importance therefore went beyond replacing Latin words with French ones: she made difficult material more accessible while explaining and examining the scientific ideas within it.