Gay-Lussac's law
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Heat a sealed rigid container of gas and the pressure climbs. It is the physics behind the warning on an aerosol can not to throw it into a fire: the trapped gas cannot expand, so heating it just makes the pressure soar until the can bursts.
Precisely: at constant volume and a fixed amount of gas, pressure is directly proportional to absolute temperature, P / T = constant, or P1/T1 = P2/T2, with T in kelvin. It was stated around 1808.
It is the isochoric (constant-volume) slice of the ideal gas law, the case where V and n stay fixed. Molecular picture: hotter means faster molecules striking the walls harder and more often, so the pressure rises.
A car tyre warms up as you drive, and its pressure rises along with the temperature even though the volume barely changes.
At fixed volume, P is proportional to absolute temperature.
This law is sometimes also called Amontons' law, and, like the others, it needs the temperature in kelvin.