Nicolas Léonard Sadi Carnot

Born June 1, 1796, in Paris; died there Aug. 24, 1832. French physicist. One of the founders of thermodynamics. Son of L. N. Carnot.

In 1814, Carnot graduated from the Ecole Poly technique in Paris and won appointment to the engineering corps. He left military service in 1828. In his only published work, Reflections on the Motive Power of Fire and on the Machines Capable of Developing This Power (1824), he considered in general form the question of “producing motion from heat.” In his analysis of the ideal cyclic process (Carnot cycle), he was the first to reach the conclusion that useful work is produced only when heat moves from a heated body to a colder body. Carnot also advanced the hypothesis that the amount of work is due to the temperature difference between the heater and the cooler and does not depend on the nature of the substance used in the heat engine. Carnot adhered in his reasoning to the caloric (thermogen) theory, but subsequently, as can be seen from his notes, which were published posthumously, he rejected this theory, recognizing the interconvertibility of heat and mechanical work. Carnot gave an approximate definition of the mechanical equivalent of heat and set forth, in general form, the law of the conservation of energy. Carnot’s work was appreciated only in 1834, when B. P. E. Clapeyron, following Carnot’s reasoning, introduced a graphic method of describing the processes. Later, by developing Carnot’s doctrine, R. Clausius and W. Thompson (Lord Kelvin) derived the second law of thermodynamics.