Jean Rey (c. 1583 - c. 1645) was a French physician and chemist. Born at Le Bugue, in the Périgord (Dordogne département), he studied medicine at the University of Montpellier. He practised medicine in his native town and corresponded with Descartes and Mersenne. He discovered that the weight of lead and tin increases when they are calcinated, and attributed this phenomenon to the weight of air, which he believed to become more dense when heated (Essays, 1630). He explained the greater weight of calcinated lead and tin by supposing that calcination involves the incorporation of air in the metal. This hypothesis would later be confirmed by Lavoisier, over a century later in 1789. His discovery of the weight of air also made possible the invention of the barometer by Torricelli in 1643. He also developed a device called a "Thermoscope", a precursor of the thermometer. Jean Rey died at Le Bugue, where he had lived all his life.
