''Reflections on the Motive Power of Fire and on Machines Fitted to Develop that Power'' () is a scientific treatise written by the French military engineer Sadi Carnot.
full text of 1897 ed.
( Full text of 1897 edition on Wikisource ) Published in 1824 in French, the short book (118 pages in the original) sought to advance a rational theory of

heat engine A heat engine is a system that transfers thermal energy to do mechanical or electrical work. While originally conceived in the context of mechanical energy, the concept of the heat engine has been applied to various other kinds of energy, pa ...

s. At the time, heat engines had acquired great technological and economic importance, but very little was understood about them from the point of view of

physics Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...

. Carnot's ''Reflections'' is now widely regarded as a key document in the development of modern thermodynamics, and Carnot himself (who published nothing else during his lifetime) has often been identified as the "father of thermodynamics". The book introduced such concepts as

thermodynamic efficiency In thermodynamics, the thermal efficiency (\eta_) is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, steam turbine, steam engine, boiler, furnace, refrigerator, ACs etc. For a he ...

, reversible processes, the

thermodynamic cycle A thermodynamic cycle consists of linked sequences of thermodynamic processes that involve heat transfer, transfer of heat and work (physics), work into and out of the system, while varying pressure, temperature, and other state variables within t ...

, and Carnot's theorem.

Overview

The book is considered the founding work of

thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed b ...

. It contains the preliminary outline of the

second law of thermodynamics The second law of thermodynamics is a physical law based on Universal (metaphysics), universal empirical observation concerning heat and Energy transformation, energy interconversions. A simple statement of the law is that heat always flows spont ...

. Carnot stated that motive power is due to the fall of caloric (''chute de calorique'') from a hot to a cold body, which he analogized to the work done by a

water wheel A water wheel is a machine for converting the kinetic energy of flowing or falling water into useful forms of power, often in a watermill. A water wheel consists of a large wheel (usually constructed from wood or metal), with numerous b ...

due to a waterfall (''chute d'eau''). Despite the fact that the caloric theory of heat was incorrect, Carnot's work brought together three insights that remain relevant and were used by his successors to develop the concept of

entropy Entropy is a scientific concept, most commonly associated with states of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynamics, where it was first recognized, to the micros ...

: * The "fall of heat" from a high temperature to a lower temperature is where the work comes from. * Analyzing a cycle, rather than an open system, is the correct way to analyze a heat engine. * The concept of a reversible process. Similar to how the ''Reflections'' was the precursor to the second law, English physicist James Joule's 1843 paper '' Mechanical equivalent of heat'' was the precursor to the

first law of thermodynamics The first law of thermodynamics is a formulation of the law of conservation of energy in the context of thermodynamic processes. For a thermodynamic process affecting a thermodynamic system without transfer of matter, the law distinguishes two ...

. In his essay, Carnot also derived the result that later came to be known as the Clausius-Clapeyron relation.

Influence

Carnot's essay received very little attention during Carnot's lifetime. Carnot published nothing else and died in 1832, at the age of 36. However, in 1834 a French mining engineer, Émile Clapeyron, published a ''Memoir on the Motive Power of Heat'' that presented Carnot's analysis graphically. The German physicist

Rudolf Clausius Rudolf Julius Emanuel Clausius (; 2 January 1822 – 24 August 1888) was a German physicist and mathematician and is considered one of the central founding fathers of the science of thermodynamics. By his restatement of Sadi Carnot's principle ...

learned of Carnot's work through Clapeyron's memoir. Clausius corrected Carnot's theory by replacing the conservation of caloric with the work-heat equivalence (i.e., energy conservation). Clausius also put the second law of thermodynamics into mathematical form by defining the concept of

. That work appeared in 1850 in Clausius's ''Mechanical Theory of Heat''.

(1867)
''The Mechanical Theory of Heat – with its Applications to the Steam Engine and to Physical Properties of Bodies''
London: John van Voorst, 1 Paternoster Row. MDCCCLXVII. Another highly influential commentary on Carnot's essay (also through Clapeyron's memoir) was published in 1849 by William Thomson (the future

Lord Kelvin William Thomson, 1st Baron Kelvin (26 June 182417 December 1907), was a British mathematician, Mathematical physics, mathematical physicist and engineer. Born in Belfast, he was the Professor of Natural Philosophy (Glasgow), professor of Natur ...

), in a paper titled ''An Account of Carnot's Theory of the Motive Power of Heat.'' In that paper, Kelvin said of Carnot's derivation of what would later be called the "Clausius-Clapeyron equation" that "nothing in the whole range of Natural Philosophy is more remarkable than the establishment of general laws by such a process of reasoning." Because of their respective commentary's on Carnot's essay, modern textbooks on thermodynamics usually introduce a "Clausius statement" and a "Kelvin statement" of the second law of thermodynamics. These statements appear to be different, but they can be shown to be logically equivalent, by an argument based on the Carnot cycle.

References

External links

* ''Reflections on the Motive Power of Fire'' (1824), analysed on
BibNum
' (click "À télécharger" for English analysis) * American Institute of Physics, 2011. {{ISBN, 978-0-7354-0985-9. Abstract at

Full article (24 page

, also a

__NOTOC__ Thermodynamics literature Physics books

Overview

Influence

See also

References

External links