Nicolas Léonard Sadi Carnot, known as Sadi Carnot, was a French military engineer and physicist. A graduate of the École polytechnique, Carnot served as an officer in the Engineering Arm of the French Army. He also pursued scientific studies, and in June 1824 published an essay titled Reflections on the Motive Power of Fire. In that book, which would be his only publication, Carnot developed the first successful theory of the maximum efficiency of heat engines.