born Dec. 6, 1778, Saint-Léonard-de-Noblat, France
died May 9, 1850, Paris
French chemist and physicist.
He showed that all gases expand by the same fraction of their volume for a given temperature increase; this led to the devising of a new temperature scale whose profound thermodynamic significance was later established by Lord Kelvin . Taking measurements from a balloon flying more than 20,000 ft (6,000 m) high, he concluded that Earth's magnetic intensity and atmospheric composition were constant to that altitude. With Alexander von Humboldt , he determined the proportions of hydrogen and oxygen in water. He is remembered as a pioneer investigator of the behaviour of gases and techniques of chemical analysis and a founder of meteorology.