“[F]rom Carnot's point of view, it is evident that the motive power of heat depends upon its being transferred from one body to another through the medium by whose change of volume or form the external mechanical effect is produced, as this medium is supposed to remain at the end of the operation in precisely the same state as at the commencement. He gives as analogous the instance of work derived from water falling from a higher to a lower level.”

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.