Nicolas Léonard Sadi Carnot, born on June 1, 1796, in Paris, France, was a pioneering French physicist and military engineer. He is widely recognized as the “father of thermodynamics” due to his foundational work on the theoretical efficiency of heat engines.
Carnot came from a distinguished family with strong ties to both science and politics. His father was Lazare Carnot, an eminent mathematician, military engineer, and a prominent leader during the French Revolutionary Army, even serving as a member of the Directory, the French Revolutionary government. Sadi was also the elder brother of statesman Hippolyte Carnot and the uncle of Marie François Sadi Carnot, who later served as President of France.
Sadi’s early life was marked by political unrest and changes in his family’s fortunes, including his father’s exile. Lazare Carnot, a writer on mathematics and mechanics, personally directed much of Sadi’s early education. At the age of 16, Sadi became a cadet at the prestigious École Polytechnique in Paris, an institution dedicated to training military engineers. His classmates included notable figures such as Michel Chasles and Gaspard-Gustave Coriolis.
After graduating, Carnot joined the Engineering Arm of the French Army. However, his career in the military was not particularly distinguished, partly due to his father’s political affiliations which made him appear “unreliable” to the restored Bourbon monarchy. He was often assigned to routine garrison duties and tasked with inspecting fortifications, tracing plans, and writing reports, many of which seemed to be ignored. He took a six-month leave in 1818 to prepare for the entrance examination to the Royal Corps of Staff and School of Application for the Service of the General Staff, which he passed, joining the General Staff in 1819 with the rank of lieutenant.
Despite his military duties, Carnot dedicated most of his attention to private intellectual pursuits, particularly his interest in steam engines. He believed that the inferiority of French steam engines, compared to British ones, contributed to Napoleon’s downfall and his family’s subsequent loss of prestige. This motivation fueled his scientific inquiries. In 1824, at the age of 28, he published his only work, Réflexions sur la Puissance Motrice du Feu (“Reflections on the Motive Power of Fire”). In this seminal work, Carnot developed the first successful theory of the maximum efficiency of heat engines, introducing the concept of the “Carnot engine” – an ideal heat engine. He demonstrated that the efficiency of such an engine depends only on the temperature difference between the heat source and the heat sink, and not on the working substance used (like steam).
Carnot’s work received little recognition during his lifetime. He retired from the army in 1828 without a pension. Sadly, his life was cut short when he died during a cholera epidemic on August 24, 1832, at the age of 36. Due to the contagious nature of cholera, many of his belongings and writings were buried with him, resulting in the loss of valuable scientific notes.
However, his genius was eventually recognized. In 1834, two years after his death, a detailed commentary and explanation of his work was published by fellow French engineer Émile Clapeyron. This brought attention to Carnot’s groundbreaking insights, which were later extensively utilized by Lord Kelvin and Rudolf Clausius in the 1840s and 1850s to formulate the foundational concepts of modern thermodynamics, including the Second Law of Thermodynamics. Today, Sadi Carnot is rightfully celebrated as a pivotal figure in the history of science.
