 Lavoisier's prestige and the practical success of Sadi Carnot's caloric theory of the heat engine since 1824 ensured that the young Joule, working outside either academia or the engineering profession, had a difficult road ahead.Supporters of the caloric theory readily pointed to the symmetry of the Peltier–Seebeck effect to claim that heat and current were convertible in an, at least approximately, reversible process.Further experiments and measurements with his electric motor led Joule to estimate the "mechanical equivalent of heat" as 4.1868 joules per calorie of work to raise the temperature of one gram of water by one Kelvin.