“If we consider any case in which mechanical effect is obtained from a thermal origin, by means of the alternate expansions and contractions of any substance whatever, and follow a perfectly rigorous process of reasoning indicated by Carnot, we arrive at the following conclusion...The thermal agency by which mechanical effect may be obtained, is the transference of heat from one body to another at a lower temperature.”

French military engineer and physicist

Nicolas Léonard Sadi Carnot, known as Sadi Carnot, was a French military engineer and physicist. He was active in the early 19th century and is remembered for his work on the science of heat. A graduate of the École polytechnique, he served as an officer in the Engineering Arm of the French Army while also pursuing scientific study. In June 1824, he published Reflections on the Motive Power of Fire, his only book, where he set out the first successful theory of the maximum efficiency of heat engines.