The direct relationship between pressure and temperature for an ideal gas was discovered by Joseph Louis Gay-Lussac in the early 1800's. The pressure of a fixed amount of an ideal gas is directly proportional to its absolute temperature at constant volume (P/T=k). Gay-Lussac's law is modeled mathematically as a direct linear relationship (Pressure=k*Temperature).

Gay-Lussac's Law (by John L. Park).