“[Thomson] found that Carnot’s proposition could no longer be proved by denying the possibility of “the perpetual motion,” and was led to lay down a second fundamental principle to serve in the demonstration. This principle [published in Thomson's memoir of March, 1851] is now called the Second Law of Thermodynamics.”

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.