Prevost Theory of heat Exchange

According to Prevost, a body emits heat radiations at all temperatures which is independent of surroundings but the quantity of heat radiated per second depends on the temperature of the body. The rate of radiation is greater at a higher temperature than at a lower one. At the same time, the body absorbs thermal radiation from the surrounding. If the rate of emission by the body is less than the rate of absorption from surroundings, there is a net heat gained by the body and its temperature rises. Conversely, if the body is emitting at the rate higher than the absorption from the surroundings, there is a net loss of heat, therefore, there is a fall of temperature of the body. The rate of emission will be greater if the temperature of the body is higher than that of the surrounding and vice-versa.

If the body temperature is equal to the temperature of surroundings, the rate of emission and the rate of absorption will be equal and temperature of the body remains constant. Thus, thermal equilibrium between the objects is not static equilibrium but a dynamic equilibrium since they are exchanging heat at the same rate resulting constant temperature of the body.