Henri Victor Regnault ForMemRS (21 July 1810 – 19 January 1878)[1] was a French chemist and physicist best known for his careful measurements of the thermal properties of gases.

Born in Aix-la-Chapelle in 1810 (modern Aachen, Germany and at that time under French rule), he moved to Paris at the age of eight, following the death of his parents.

[3] Regnault received the Rumford Medal of the Royal Society of London and appointment as Chief Engineer of Mines.

He designed sensitive thermometers, hygrometers, hypsometers and calorimeters, and measured the specific heats of many substances and the coefficient of thermal expansion of gases.

In the course of this work, he discovered that not all gases expand equally when heated and that Boyle's law is only an approximation, especially at temperatures near a substance's boiling point.