Charles' data suggest that, if a gas continued to behave at lower temperatures in the way that it does at room temperature, its volume would shrink to nothing at -273. This is the point at which, in principle, all molecules would come to rest and gases would cease to exert pressure or occupy volume.

This theoretically possible but experimentally unattainable temperature is known as absolute zero. We can define an absolute temperature scale (also known as the Kelvin scale after the British thermodynamicist Lord Kelvin), in which the temperature (T) in degrees absolute or Kelvin (K) is related to the temperature in degrees centigrade (t) by the expression

T(K) = t () + 273.15




Top Right: Jacques Charles (1746 - 1823)
Bottom Right: Lord Kelvin (1824 - 1907)