Jacque Charles was a French physicist, inventor, and mathematician who, with Nicholas Robert, made the first ascent in a hydrogen balloon (1783). He discovered the law relating the expansion of a gas to its temperature rise. Gay-Lussac published this work some 15 years after Charles' discovery and it is alternately known as Charles' law or Gay-Lussac's law. Charles is credited with inventing a thermometric hydrometer and improving Fahrenheit's aerometer and Gravesande's hydrometer.

 

Charles' law

Charles' law states that for a gas held at constant pressure, the volume (V) occupied by the gas is directly proportional to its temperature (T). That is:

 

    V ∝ T, or
    V/T = k,
    where k is a constant.

 

The relationship was discovered by Charles in 1787 and is a special case of the ideal gas law. It is sometimes called Gay-Lussac's law, because Joseph Gay-Lussac established it more accurately in 1882.