Charles, Jacques Alexandre César (1746-1823)

French physicist who studied gases and made the first ascent in a hydrogen-filled balloon in 1783. His work on the expansion of gases led to the formulation of Charles's law.

Hearing of the hot-air balloons of the Montgolfier brothers, Charles and his brothers began experimenting with hydrogen balloons and made their ascent only ten days after the Montgolfiers' first flight. In later flights Charles ascended to an altitude of 3,000 m/10,000 ft.

Charles was born in Loiret and worked as a clerk at the Ministry of Finance in Paris. Stimulated by American scientist Benjamin Franklin's experiments with lightning and electricity, he constructed a range of apparatus which he demonstrated at public lectures. He went on to become professor of physics at the Paris Conservatoire des Arts et Métiers.

In about 1787 Charles experimented with hydrogen, oxygen, and nitrogen, and found that a gas expands by 1/273 of its volume at 0°C for each degree rise in temperature. He communicated this to physical chemist Joseph Gay-Lussac, who repeated the experiments and published the result. Charles's law is therefore sometimes known as Gay-Lussac's law.