Jacques-Alexandre Charles was born November 12, 1746, in Beaugency, France and died April 7, 1823, in Paris. He was a mathematician, physicist, and inventor. With the Robert brothers, Nicolas and Anne-Jean, he built one of the first hydrogen balloons. Along with Nicolas Robert, he was the first to ascend in a hydrogen balloon in 1783. In the course of several flights he rose to an altitude of more than a mile.
From clerking in the finance ministry, he turned to science and experimented with electricity. He produced several inventions, including a hydrometer and reflecting goniometer, and improved the Gravesande's heliostat and Fahrenheit's aerometer. He was elected in 1795 to the Academie des Sciences, Paris, and subsequently became a professor of physics. His published papers mainly concerned mathematics.
About 1787 he developed Charles' law concerning the expansion of gasses. Charles' law is a statement that the volume occupied by a fixed amount of gas is directly proportional to its absolute temperature, under conditions of constant pressure. This empirical relation was formulated first by Charles about 1787, and later by Joseph Gay-Lussac. It is a special case of the general gas law, which states that the product of the absolute temperature (t) and a constant equals the product of the pressure (p) and the volume (v) or pv=kt, and can be derived from the kinetic theory of gasses under the assumption of a perfect (ideal) gas. Measurements show that, at constant pressure, the thermal expansion of real gasses is nearly the same at sufficiently low pressure and high temperature, showing that Charles's law is approximately valid.