Sadi Carnot
Nicolas Léonard Sadi Carnot was a French engineer and physicist born on June 1, 1796, in Paris. He is often referred to as the "father of thermodynamics" for his groundbreaking work on heat engines, particularly articulated in his sole scientific publication, **Réflexions sur la puissance motrice du feu** (Reflections on the Motive Power of Fire), published in 1824. In this seminal work, Carnot established that the efficiency of a heat engine depends on the temperature difference between its heat source and heat sink, introducing a formula that laid the foundation for the study of thermodynamics. Despite his contributions, Carnot's work went largely unrecognized during his lifetime and was only acknowledged years later, influencing future physicists like William Thomson and Rudolf Clausius.
Carnot's early education was significantly shaped by his father, a prominent figure during the French Revolutionary Wars, and he later studied at the prestigious École Polytechnique. His career in military engineering involved assessing fortifications and drafting plans, but he devoted much of his free time to studying physics. Tragically, his life was cut short by illness; he passed away from cholera on August 24, 1832. Carnot's legacy endures, as his insights into heat and work remain fundamental to modern physics.
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Sadi Carnot
Dates: 1796–1832.
Summary: Sadi Carnot was a French mathematician who is also referred to as the Father of Thermodynamics. He studied the transfer of heat when researching how to make a steam engine most efficient.
Nicolas Leonard Sadi Carnot was born in the Palais du Petit-Luxembourg, Paris, on June 1, 1796, the eldest son of Lazare Nicolas Marguerite Carnot (1753–1823), the Organizer of the Victory of the French Revolutionary Wars. His father was a member of the Directory, and a surviving member of the Committee of Public Safety. His younger brother, Lazare Hippolyte Carnot (1801–88), would become an important politician and preserved some of Sadi’s notes among his papers. Lazare Carnot resigned from politics in 1807 in order to attend to the education of his sons. Sadi was taught at home by his father, who had written on scientific and engineering problems. He had also studied the efficiency of water machines. The idea of work derived from falling water was Sadi’s model for work on a heat engine caused by falling heat.
Sadi attended the Lycée Charlemagne in Paris in order to prepare for the entrance examination to the École Polytechnique, which he entered in 1812. In 1813, Sadi sought permission from Napoleon to join with other young students in defending France. In March 1814, he fought at Vincennes in the Battle of Paris. In October 1814, he graduated as a military engineer. His studies at the École Polytechnique placed him in the company of some of France’s best scientists, including Siméon-Denis Poisson, Joseph Gay-Lussac, and André-Marie Ampère. Posted to the École du Genie at Metz as a student second lieutenant, he wrote several scientific papers that are no longer extant. During the Hundred Days, Lazare Carnot served as Napoleon’s minister of the interior, but was exiled in October 1815, following the Restoration. This ended the special attention Sadi’s superiors had previously given to him.
When his studies ended in 1816, Sadi began serving in the Metz engineering regiment as a second lieutenant. For several years, he moved from garrison to garrison inspecting fortifications, drafting plans, and writing reports that were thereafter neglected in bureaucratic files. In 1819, he was assigned to the general staff in Paris. He immediately gained a permanent leave of absence, which allowed him time to engage in studying physics. Between 1818 and 1824, Carnot spent many hours studying the steam engine, which had been invented by James Watt (1736–1819). Hailed as the technology of the future, it was a very inefficient machine that lost most of its heat energy. Carnot sought to improve its efficiency by seeking to understand the nature of heat.
In 1824, Carnot published Réflexions sur la puissance motrice du feu et sur les machines propres a developer cette puissance (Reflections on the Motive Power of Fire). In the title word “fire,” Carnot meant heat, and by “motive power,” he meant work. The book was his only scientific work. Published by Bachelier, the most important French scientific publisher, it was well received, formally presented to the Academie des Sciences, and favorably reviewed by P.-S. Girard in the Revue encyclopedique. Réflexions showed that the efficiency of a heat engine, that is, an engine that changes heat into mechanical energy in order to do work, was dependent upon the difference between its hottest and coolest temperature. Using the formula T1-T2/T2, Carnot expressed the efficiency between the hottest temperature, T1, and coolest temperature, T2. The equation is considered to be the first statement of the theory of heat movement. Consequently, Carnot is considered the father of the science of thermodynamics. The equation was universal because it applied to any heat engine and any temperature. At the end of his Réflexions, Carnot included a definition of work. It was defined as weight that was lifted to some height. In modern physics, work is the force that is applied to a body through a distance against resistance.
French army reorganization in 1827 put Carnot back on active duty. This prevented him from engaging in more scientific studies until 1828, when he resigned. He then spent his time studying the relationship between temperature and pressure. His researches were cut short when he contracted scarlet fever. He had not yet recovered when a cholera epidemic swept across Paris, taking his life. He died in Paris on August, 24, 1832. His scientific papers and all of his possessions were burned, as was the practice in an effort to purge the disease with fire. Carnot’s work in thermodynamics was generally ignored until 1848 when William Thomson (Lord Kelvin) was influenced by it as he studied heat for an absolute temperature scale, the Kelvin scale. The German physicistRudolf Clausius later modified Carnot’s work and spread his ideas as the second law of thermodynamics: Entropy occurs because heat cannot move from a colder substance to a hotter substance.
Bibliography
Carnot, Sadi. Reflection on the Motive Power of Fire. New York: Dover, 1960.
Cropper, William H. Great Physicists: The Life and Times of Leading Physicists From Galileo to Hawking. New York: Oxford University Press, 2001.
Hatfield, Philipp L. Great Men of Science: A History of Scientific Progress. New York: Macmillan, 1933.
Mendoza, E., ed. Reflections on the Motive Power of Fire by Sadi Carnot, and Other Papers on the Second Law of Thermodynamics by E. Clapeyron and R. Claissius. New York: Dover Publications, 1960.