Charles, Jacques Alexandre César (zhäk älĕksäNˈdrə sāzärˈ shärl) [key], 1746–1823, French physicist. He confirmed Benjamin Franklin's electrical experiments, became interested in aeronautics, and was the first to use hydrogen gas in balloons. In this type of balloon, known as the Charlière, he made an ascent in 1783 of almost 2 mi (3.2 km). He became professor of physics at the Conservatoire des Arts et Métiers, Paris. Inventor of a thermometric hydrometer, he also improved various devices, the Gravesande heliostat and Fahrenheit's aerometer among others, and anticipated Gay-Lussac's law of the expansion of gases. For Charles's law, see gas laws.