Boyle–Mariotte law, one of the fundamental gas laws, according to which at constant temperature T the volume V of a given mass of gas is inversely proportional to its pressure p, pV=const (Fig.). It was established by the English scientist R. Boyle in 1662 and was also formulated in 1676 by the French physicist E. Mariotte. It holds strictly only for an ideal gas. For real gases, whose molecular volume and intermolecular interaction cannot be neglected, the Boyle–Mariotte law holds approximately — the better, the further the gas is from the critical state. The Boyle–Mariotte law describes an isothermal process in a gas and follows from the kinetic theory of gases.
The dependence of the volume V on the pressure p for a constant mass of gas at temperatures T1<T2<T3. The isotherms T1, T2, T3 have the form of rectangular hyperbolas; the areas A1 and A2 are equal.