Charles observed that the volume of certain amount of a gas changes by V_{O} / 273.15 for each

degree rise or fall in temperature.V_{O} being the volume at 0°C.The volume at any temperature t°C

is given by

V_{t} = V_{O}(1 + t°C/ 273.15)

Now ,if the temperature is lowered,it becomes clear that at t = -273.15°C

V_{t} = V_{O}(1+ (-273.15/273.15))

= V_{O} = (1-1) = 0

And below t = -273.15°C, Vt becomes negative, which is not possible

Therefore the physically significant lowest temperature is -273.15° C