Sadi Carnot (1796-1832) was a young French military engineer, son of that Lazare Carnot whom the revolutionary wars had nicknamed “the organiser of victory”. Raised during the height of the Napoleonic Empire and a witness to its fall, Carnot burned with the humiliation that English steam engines were more efficient than French ones. It was precisely this national rivalry between France and England that drove him to seek the fundamental laws of heat (Guillen 1995, pp. 172-173) Riferimenti bibliografici.
In 1824, at just 28 years old, he published the Réflexions sur la puissance motrice du feu. His decisive insight: the efficiency of a heat engine depends only on the temperature difference between the hot source and the cold source, not on the working fluid used. This is the core of what would become the second law of thermodynamics (Simonyi 2012, pp. 373-374).
Carnot died of cholera at 36, in almost total obscurity. It was only thirty years later that Clausius and Lord Kelvin recognised the revolutionary scope of his work, giving it the mathematical form we still study today (Buchwald and Fox 2014, ch. 4).
Historical context
Carnot’s reasoning is revolutionary because it does not start from the concrete working of a machine in order to calculate its losses: it starts from an abstraction — the ideal reversible cycle — and shows that no real machine can ever do better. An impossibility argument that twentieth-century physics would inherit as one of its distinctive tools.
Linked notes
Topics: Macchine termiche Concepts: Ciclo di Carnot · Secondo principio della termodinamica
Related exercises: Problema — Una macchina troppo efficiente · Problema — Vero o falso su macchine e frigoriferi · Problema — Carnot rispetto agli altri cicli