ALT Émilie du Châtelet was well known and well respected in the scientific community in the mid 1700s, but unfortunately nowadays she is most famous for her romantic affair with Voltaire. Her translation of Isaac Newton's Philosophiae Naturalis Principia Mathematica remains the standard French text today. In the year 1749, Du Châtelet worked 18 hour days in the late stages of her pregnancy in order to complete the translation, which she managed just days before she died in childbirth aged 42. This was not only a translation of Newton's ideas - she also added 237 pages of commentary where, amongst other things, she advocated for the concept of kinetic energy. Newton's work in fact only assumed the conservation of mechanical momentum, and he and earlier thinkers believed that energy and momentum were indistinct, and both proportional to velocity.