The birth of thermodynamics and Clausius | Tangente

The industrial use of heat is recent, although the first steam engine was built in antiquity (in the 1^st century CE). At the time, however, no one foresaw the extraordinary potential of the machine presented by Hero of Alexandria, based on a model proposed by Vitruvius a century earlier. Eighteen centuries later, even as James Watt (1736–1819) was working to improve his steam engine, the economist and philosopher Adam Smith, at the same university as Watt, curiously made no mention of it in his celebrated essay Richesse des nations (1776), entirely failing to glimpse that this was where the future of industry lay. The first developments of what would become thermodynamics emerged in France at the end of the 18^th century. The name is particularly apt, evoking both heat and motion.

Heat is not a material fluid -------------------------------------------

When he was not sitting in the National Convention (where he voted for the death of Louis XVI on January 16, 1793), the mathematician and physicist Lazare Carnot devoted himself as readily to the study and operation of very real machines as to infinitesimal calculus and geometry. His admiration for the 12^th-century Persian poet Saadi of Shiraz (who was enslaved by the Crusaders in Acre, now in Israel) led him to name his first son Sadi. From an early age, his son likewise developed a passion for studying steam engines, notably publishing a short essay entitled Réflexions sur la puissance motrice du feu (1824). The young scholar's treatise abounds in mistaken ideas, since Sadi Carnot regarded heat as a kind of material fluid that was conserved and produced energy, in keeping with the thinking of most scientists of his day. Yet it also contains a fundamental insight: steam engines work because heat passes from hot to cold. It was this same Sadi Carnot who, a little later (1831), stated the first law of thermodynamics, namely the conservation of energy in heat exchanges: the amount of kinetic energy that can be extracted from a heat engine as motion cannot exceed the amount of energy supplied as heat.

Lazare Carnot: committed politician and versatile mathematician ------------------------------------------------------------------

The French scientist and politician Lazare Carnot ended his days in exile as a regicide, having voted for the death of Louis XVI in the National Convention. The titles of his many publications reveal the full range of scientific fields he successfully explored: Essai sur les machines en général (1786) ; Réflexions sur la métaphysique du calcul infinitésimal (1797); while De la corrélation des figures de géométrie (1801) and Géométrie de position (1803) are two contributions to the development of a modern view of geometry... Lazare Carnot's descendants include many leading figures in science and politics.

Bust of Lazare Nicolas Marguerite Carnot (1753–1823).

Sadi Carnot, the inventor of thermodynamics ----------------------------------------------

Nicolas-Léonard Sadi Carnot (1796–1832) was Lazare Carnot's eldest son (see above). He succumbed to the cholera epidemic of 1832. He should not be confused with his nephew, the future president of the French Republic Marie François Sadi Carnot (1837–1894), who was assassinated while in office.

His only work, *Réflexions sur la puissance motrice du feu et sur les moyens propres à développer cette puissance, published in 1824, gave rise to thermodynamics and contained what is now known as the Carnot principle, as well as describing the Carnot cycle. The name Carnot's theorem, meanwhile, applies to three results, two of which (the Japanese theorem and the theorem of concurrent perpendiculars*) were the work of his father, Lazare, while the third refers to the Clausius inequality.