Jacques Alexandre C矇sar Charles (November 12, 1746 - April 7, 1823) was a French inventor, scientist, mathematician, and balloonist. Charles conceived the idea that hydrogen would be a suitable lifting agent for balloons having studied the work of Robert Boyle's Boyle's Law which was published 100 years earlier in 1662. Charles and the Robert brothers launched the world's first (unmanned) hydrogen-filled balloon in August 1783. In December 1783, he and his co-pilot Nicolas-Louis Robert ascended to a height of about 1,800 feet in a manned balloon. Charles's law, describing how gases tend to expand when heated, was formulated by Joseph Louis Gay-Lussac in 1802, but he credited it to unpublished work by Jacques Charles. Charles was elected to the Acad矇mie des Sciences, in 1793, and subsequently became professor of physics at the Conservatoire des Arts et M矇tiers. He developed several useful inventions, including a valve to let hydrogen out of the balloon and other devices, such as the hydrometer and reflecting goniometer, and improved the Gravesand heliostat and Fahrenheit's aerometer. In addition he confirmed Benjamin Franklin's electrical experiments. He died in 1823 at the age of 76.