Gas dioxide, and air expand to the same extent over the same 80 kelvin interval. He noted that, for an ideal gas at constant pressure, the volume is directly proportional to its temperature: In 1802, Joseph Louis Gay-Lussac published results of similar, though more extensive experiments. Gay-Lussac credited Charles' earlier work by naming the law in his honor. Gay-Lussac himself is credited with the law describing pressure, which he found in 1809. It states that the pressure exerted on a container's sides by an ideal gas is proportional to its temperature. In 1811, Amedeo Avogadro verified that equal volumes of pure
Zeroth law of thermodynamics that provides a continuous ordering of states. The dimensionality of a surface of constant temperature is one less than the number of thermodynamic parameters, thus, for an ideal gas described with three thermodynamic parameters "P", "V" and "N", it is a two-dimensional surface. For example, if two systems of ideal gases are in equilibrium, then = where "P" is the pressure in the "i"th system, "V" is the volume, and "N" is the amount (in moles, or simply the number of atoms) of gas. The surface = constant defines surfaces of equal thermodynamic temperature, and one may label defining "T"