“In the nineteenth century Sadi Carnot combined the old idea that perpetual-motion machines are impossible (an early and incomplete version of the first law) with the {{w|caloric theory}} (heat is a substance) to prove that in a heat engine a discharge of heat to the cold surroundings was inevitable. From this starting point, he and others deduced some remarkable conclusions about the efficiency of heat engines and about the properties of matter...”

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.