Nicolas Léonard Sadi Carnot was a French military engineer and physicist. He is often described as the "father of thermodynamics". He gave the first successful theory of the maximum efficiency of heat engines.
Background
Carnot was born on June 1, 1796, in Paris, the eldest son of Lazare Carnot, a member of the Directory. He was given the name Sadi because of the admiration of his father for Sadi (Muslihal-Din), a medieval Persian poet and moralist. The powerful and often turbulent worlds of French politics and science were an integral part of the environment in which Sadi and his younger brother Hippolyte spent their youth. Withdrawing from public life in 1807, Lazare Carnot concentrated on science and the education of his sons.
Education
Through his studies, Sadi acquired not only his taste and aptitude for mathematics but also a solid training in physics, the natural sciences, languages, and music.
Because of his rapid progress, it was decided that Sadi should attend the elite École Polytechnique upon attaining the age of sixteen, the minimum for admission. Following a few months’ preparation at the Lycée Charlemagne in Paris, he passed the entrance examination and was admitted to the Polytechnique. His studies there from 1812 to 1814 stressed analysis, mechanics, descriptive geometry, and chemistry, taught by a distinguished faculty including Poisson, Gay-Lussac, Ampère, and Arago. In 1813 Sadi addressed a letter to Napoleon on behalf of his fellow students, asking permission to join the fight against the invading Allies, and in March 1814 he was among the students who fought bravely, though in vain, at Vincennes.
Ranking sixth in his class, he finished his studies at the Polytechnique in October 1814 and was immediately sent to the École du Génie at Metz as a student second lieutenant. During the two-year course in military engineering Sadi wrote several scientific papers, now lost but which his brother said were well received.
Career
During the Hundred Days, Lazare Carnot was Napoleon’s minister of the interior, and Sadi became an object of special attention from his superiors. This ended in October 1815, when Lazare was exiled by the Restoration.
In late 1816 Sadi finished his studies and began serving as a second lieutenant in the Metz engineering regiment. For the next two years he was shifted about from garrison to garrison, inspecting fortifications and drawing up plans and reports doomed to bureaucratic oblivion. In spite of some connections with high officials, his father’s name and reputation became a burden to him in the first years of the Restoration, and his intellectual development was frustrated by the tedium of military garrisons. In 1819 he seized an opportunity to escape by passing a competitive examination for appointment to the army general staff corps in Paris. He immediately obtained a permanent leave of absence and took up residence in his father’s former Paris apartment.
Relieved of the constraints of military life, Carnot began the wide range of study and research that continued, despite numerous interruptions, until his death. In addition to private study he followed courses at the Sorbonne, the Collège de France, the École des Mines, and the Conservatoire des Arts et Métiers. At the latter he became a friend of Nicolas Clément, who taught the course in applied chemistry and was then doing important research on steam engines and the theory of gases. One of Carnot’s particular interests was industrial development, which he studied in all of its ramifications. He made frequent visits to factories and workshops, studied the latest theories of political economy, and left in his notes detailed proposals on such current problems as tax reform. Beyond this, his activity and ability embraced mathematics and the fine arts.
In 1821 Carnot interrupted his studies to spend a few weeks with his exiled father and brother in Magdeburg. It was apparently after this visit that, once again in Paris, he began to concentrate on the problems of the steam engine. After Lazare’s death in August 1823, Hippolyte returned to Paris to find his brother at work on the manuscript of the Réflexions. In an attempt to make his work comprehensible to a wide audience, Sadi forced Hippolyte to read and criticize portions of the manuscript. On 12 June 1824 the Réflexions sur la puissance motrice du feu et sur les machines propres à développer cette puissance was published by Bachelier, the leading scientific publisher in France. By all reasonable standards, the book was well received. On 14 June it was formally presented to the Académie des Sciences, and on 26 July P.S. Girard read a lengthy and very favorable review to the Academy. This review, printed in the August issue of the Revue encyclopédique, emphasized the book’s conclusions and its applications for steam-engine construction. Although the major theorems were cited, there was no discussion of the highly original reasoning that Carnot had employed. Following the publication of his book, Carnot continued his research, fragments of which are preserved in his manuscript notes. A reorganization of the general staff corps, however, forced Carnot to return to active service in 1827 with the rank of captain.
After less than a year of routine duty as a military engineer in Lyons and Auxonne, Carnot resigned permanently and returned to Paris. He again focused his attention on the problems of engine design and the theory of heat. In 1828 a contemporary referred to Carnot as a “builder of steam engines,” although there is no record of his formal connection with any firm. True to his father’s republican principles, Carnot welcomed the July Revolution but was soon disappointed with the new government. Nonetheless, he was highly regarded in some political circles, for shortly after the Revolution he was mentioned as a possible member of the Chambre des Pairs. He objected to the hereditary nature of this position, however, and refused to be nominated.
In 1831 Carnot began to investigate the physical properties of gases and vapors, especially the relationship between temperature and pressure. In June 1832, however, he contracted scarlet fever. This was followed by “brain fever,” which so undermined his fragile health that on 24 August 1832 he fell victim to a cholera epidemic and died within the day, at the age of thirty-six. In accordance with the custom, his personal effects, including nearly all of his papers, were burned. Although for eight years his work had been almost completely ignored, he was not forgotten.
Religion
On Carnot's religious views, he was a Philosophical theist. As a deist, he believed in divine causality, stating that "what to an ignorant man is chance, cannot be chance to one better instructed," but he did not believe in divine punishment. He criticized established religion, though at the same time spoke in favor of "the belief in an all-powerful Being, who loves us and watches over us."
Personality
Except for his informal contact with Clement, Carnot always worked independently and rarely discussed his research. Although sensitive and perceptive, he appeared extremely introverted, even aloof, to all but a few close friends, most of whom were his classmates at the Polytechnique.