Carnot, Nicolas Léonard Sadi

Also found in: Dictionary, Thesaurus.
Related to Carnot, Nicolas Léonard Sadi: Marie Francois Sadi Carnot, Lazare Carnot

Carnot, Nicolas Léonard Sadi

(nēkōlä` lāônär` sädē` kärnō`), 1796–1832, French physicist, a founder of modern thermodynamics; son of Lazare N. M. Carnot. His famous work on the motive power of heat (Réflexions sur la puissance motrice du feu, 1824) is concerned with the relation between heat and mechanical energy. Carnot devised an ideal engine in which a gas is allowed to expand to do work, absorbing heat in the process, and is expanded again without transfer of heat but with a temperature drop. The gas is then compressed, heat being given off, and finally it is returned to its original condition by another compression, accompanied by a rise in temperature. This series of operations, known as Carnot's cycle, shows that even under ideal conditions a heat engine cannot convert into mechanical energy all the heat energy supplied to it; some of the heat energy must be rejected. This is an illustration of the second law of thermodynamics. Carnot's work anticipated that of Joule, Kelvin, and others.

Carnot, Nicolas Léonard Sadi


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.


Réflexions sur la puissance motrice du feu et sur les machines propres à développer cette puissance, new ed. Paris [1953.]
In Russian translation:
Razmyshleniia o dvizhushchei sile ognia i o mashinakh sposobnykh razvivaf etu silu. Moscow, 1923.
“Razmyshleniia o dvizhushchei sile ognia i o mashinakh sposobnykh razvivat’ etu silu.” In the collection Vtoroe nachalo termodinamiki. Moscow, 1934. Pages 17–61.


Radtsig, A. A. “Sadi Karno i ego ‘Razmyshleniia o dvizhushchei sile ognia.” In Arkhiv istorii nauki i tekhniki, fasc. 3. Leningrad, 1934.
Fradkin, L. Z. Sadi Karno: Ego zhizn ‘ / tvorchestvo: K 100-letiiu so dnia smerti, 1832–1932 gg. Moscow-Leningrad, 1932.
La Mer, V. C. “Some Current Misinterpretations of N. L. Sadi Carnot’sMemoir and Cycle.” American Journal of Physics, 1954, vol. 22, no. 1.