Emilie du Chatelet was born in 1706 to a family that considered education an appropriate hobby for daughters, which in eighteenth-century France placed her in approximately the top one percent of fortunate women. Her father arranged tutors. She learned Latin, Greek, Italian, and German. She studied mathematics with increasing seriousness through her twenties, and by her thirties she was corresponding with the leading physicists and mathematicians in Europe. She was also Voltaire's lover, which is the fact that history chose to remember, because a woman's romantic life is apparently always more interesting than her scientific one.

David Bodanis's dual biography of Chatelet and Voltaire makes the power dynamic between them clear. Voltaire was the most famous writer in Europe. Chatelet was the better scientist. They both knew it. Voltaire once described Chatelet as a great man whose only fault was being a woman, which he meant as a compliment and which tells you everything about the century she was operating in.

She Proved That Energy Depends on Velocity Squared and Nobody Listened

The Leibniz-Newton debate over the nature of kinetic energy was one of the major scientific controversies of the eighteenth century. Newton's followers held that the force of a moving object was proportional to its velocity. Leibniz argued it was proportional to the square of velocity. Chatelet designed and analyzed experiments using lead balls dropped into clay and demonstrated conclusively that Leibniz was correct. The energy of a moving object is proportional to the square of its velocity, the principle now expressed as kinetic energy equals one-half mass times velocity squared.

Judith Zinsser's biography documents the response. Chatelet published her findings. Male scientists acknowledged them reluctantly, ignored them conveniently, and attributed them to Voltaire's influence when they could not ignore them entirely. The woman who settled one of the major debates in physics was treated as a footnote in the career of her boyfriend.

She Translated Newton Into French and Made It Better

Chatelet spent the last years of her life translating Newton's Principia Mathematica into French. She did not merely translate. She annotated, corrected, and extended Newton's work, adding mathematical commentary that clarified passages Newton himself had left ambiguous. Her translation, published posthumously in 1759, remained the standard French edition of the Principia for over two centuries. It is still considered one of the finest translations of a scientific text ever produced.

Bodanis notes that the translation was an act of intellectual synthesis that required mastery of Latin, advanced mathematics, Newtonian physics, and the ability to identify and correct errors in the work of the most revered scientist who had ever lived. Chatelet did this while pregnant with her fourth child, aware that the pregnancy at her age carried significant risk, racing against a deadline she seemed to sense was real.

She Died at Forty-Two and the Work Survived the Erasure

Chatelet died in 1749, six days after giving birth, at forty-two. Voltaire was devastated. He wrote that he had lost half of himself. The scientific community responded by gradually forgetting that she had existed. Her contributions were absorbed into the general progress of physics without attribution. Her name disappeared from textbooks. For two centuries, she was remembered primarily as Voltaire's mistress, a woman of unusual intelligence who happened to be attached to a famous man.

The twentieth century corrected this, slowly. Zinsser's biography, Bodanis's narrative, and a growing body of scholarship have restored Chatelet to her proper place in the history of science: a physicist who resolved a major theoretical debate, a translator who improved Newton, and a woman who demonstrated that the Enlightenment's commitment to reason had a notable exception when it came to which humans were permitted to exercise it.