In 1792 , Pierre Prevost put forward a theory of heat exchange .
According to this theory , all bodies at all temperatures above the absolute zero temperature (0 K) radiate thermal energy to the surroundings and at the same time receive radiant energy from the surroundings.
Thus there is continuous exchange of radiant energy between a body and its surroundings.
The quantity of radiant energy ( thermal energy) emitted by a body per unit time depends upon the nature of the emitting surface, the area of the surface and the temperature of the surface.
The quantity of radiant energy absorbed by a body per unit time depends upon the nature of the absorbing surface , the area of the surface and the time rate at which the radiant energy is incident on the body.
If the time rate of emission of thermal energy is greater than the time rate of absorption of thermal energy , the temperatures of the body falls . If the emission rate equals the absorption rate the temperatures of the body remains constant.
