Nicolas Léonard Sadi Carnot (1 June 1796 – 24 August 1832) was a
French physicist and
military engineer who, in his 1824
Reflections on the Motive Power of Fire, gave the first successful theoretical account of
heat engines, now known as the
Carnot cycle, thereby laying the foundations of the
second law of thermodynamics. He is often described as the "Father of thermodynamics", being responsible for such concepts as
Carnot efficiency,
Carnot theorem,
Carnot heat engine, and others.
Born in Paris, Sadi Carnot was the first son of the eminent military leader and geometer, Lazare Nicholas Marguerite Carnot, elder brother of Hippolyte Carnot, and uncle of Marie François Sadi Carnot (President of the French Republic (1887-1894), son of Hippolyte Carnot). His father named him for the Persian poet Sadi of Shiraz (Carnot 1960, p.&_160;xi), and he was always known by this third given name.
From age 16 (1812), he lived in Paris and attended the École polytechnique where he and his contemporaries, Claude-Louis Navier and Gaspard-Gustave Coriolis, were taught by professors such as Joseph Louis Gay-Lussac, Siméon Denis Poisson and André-Marie Ampère. After graduation, he became an officer in the French army before committing himself to scientific research, becoming the most celebrated of Fourier's contemporaries who were interested in the theory of heat. Since 1814, he served in the military. Following the final defeat of Napoleon in 1815, his father went into exile. He later obtained permanent leave of absence from the French army. Subsequently, he spent time to write his book.
The historical context in which Carnot worked was that the scientific study of the steam engine hardly existed, but the engine was actually pretty far along in its development. It had attained a widely recognized economic and industrial importance. Newcomen had invented the first piston operated steam engine over a century before, in 1712. About 50 years after that, Watt made his celebrated improvements to greatly increase the efficiency and practicality of the engine. Compound engines, with more than one stage of expansion, had already been invented. There was even a crude form of an internal combustion engine, which Carnot was familiar with, and described in some detail in his book. (Carnot 1960, p.&_160;56) Amazing progress on the practical side had been made, so at least some intuitive understanding of the engine's workings existed. The scientific basis of its operation, however, was almost nonexistent even after all this time. In 1824, the principle of conservation of energy was still immature and controversial, and an exact formulation of the first law of thermodynamics was yet over a decade away. The mechanical equivalent of heat was still two decades away. The prevalent theory of heat was the caloric theory which supposed that heat was a sort of weightless, invisible fluid that flowed when out of equilibrium.
