<P> If an open system (in which mass may be exchanged with the environment) has several walls such that the mass transfer is through rigid walls separate from the heat and work transfers, then the first law may be written: </P> <Dl> <Dd> d U = δ Q − δ W + u ′ d M, (\ displaystyle \ mathrm (d) U = \ delta Q - \ delta W + u' \, dM, \,) </Dd> </Dl> <Dd> d U = δ Q − δ W + u ′ d M, (\ displaystyle \ mathrm (d) U = \ delta Q - \ delta W + u' \, dM, \,) </Dd> <P> where d M (\ displaystyle dM) is the added mass and u ′ (\ displaystyle u') is the internal energy per unit mass of the added mass, measured in the surroundings before the process . </P>

Who stated the law of conservation of energy