Charles , Jacques Alexandre César

(1746–1823) French physicist and physical chemist

Born in Beaugency, France, Charles was a clerk in the finance ministry who developed an interest in science, especially in the preparation of gases. Eventually he became professor of physics at the Conservatoire des Arts et Métiers in Paris. He constructed the first hydrogen balloons, making an ascent to over 3000 meters (1.9 mi) in 1783. This feat brought him popular fame and royal patronage.

His name is chiefly remembered, however, for his discovery ofCharles's law, which states that the volume of a fixed quantity of gas at constant pressure is inversely proportional to its temperature. Hence all gases, at the same pressure, expand equally for the same rise in temperature. Strictly speaking, the law holds only for ideal gases but it is valid for real gases at low pressures and high temperatures. Charles deduced the law in about 1787, working with oxygen, nitrogen, carbon dioxide, and hydrogen, but he did not publish it. He communicated his results to Joseph-Louis Gay-Lussac, who published his own experimental results in 1802, six months after Dalton had also deduced the law. The priority, as Gay-Lussac pointed out, belongs to Charles but Gay-Lussac's figures were more accurate (and thus the law is sometimes referred to as Gay-Lussac's law). This law and that formulated by Robert Boyle comprise the gas laws.