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
Potential temperature 1st law simplifies to: For approximately ideal gases, such as the dry air in the Earth's atmosphere, the equation of state, formula_18 can be substituted into the 1st law yielding, after some rearrangement: where the formula_20 was used and both terms were divided by the product formula_21 Integrating yields: and solving for formula_23, the temperature a parcel would acquire if moved adiabatically to the pressure level formula_24, you get: The potential virtual temperature formula_26, defined by is the theoretical potential temperature of the dry air which would have the same density as the humid air at a standard pressure P.