In existographies, Emile Clapeyron (1799-1864) (IQ:#|#) (CR:63) was a French mining engineer and physicist, noted for []

Overview

In 1834, Clapeyron, in his “Memoir on the Motive Power of Heat”, brought Sadi Carnot’s 1824 paper Reflections on the Motive Power of Fire into the public light, and with the very important use of the Watt indicator diagram (1796), employed to update graphically Carnot’s arguments. [1]

Indicator diagram
Clapeyron, is credited as being the first person to use the graph of an indicator, thermodynamically. How he learned about the indicator diagram, however, is a bit of a mystery; the following is one take on this:

“Clapeyron represented the Carnot cycle in terms of a Watt indicator diagram; the familiar form that it assumes in the introductory pages of all modern textbooks on thermodynamics. How Clapeyron came to know about the indicator diagram is an intriguing and, at present, unsolved problem in the history of science. The secret was very closely guarded by Boulton and Watt; so well in fact that was not until 1826 that a well-informed engineer like John Farey first saw an indicator diagram being taken in Russia, and in this way learned of the principle.”
— Donald Cardwell (1971), From Watt to Clausius (pg. 220) [3]

While historians, like Caldwell above, categorize this as an "unsolved" problem in the history of thermodynamics.

In 1822, Scottish engineer H.H., in his “Account of a Steam-Engine Indicator”, published in the Quarterly Journal of Science, Literature and the Arts (Ѻ), detailed the operation of the indicator, with indicator graph illustration, below left. The indicator diagram made by Clapeyron, by comparison, is shown above right.


	H.H. indicator diagram (1822)	Clapeyron indicator diagram (1834)

In 1834, Francois Pambour, in his Treatise on the Steam Locomotive, of note mentions the Watt "indicator", but only in respect to give a description of the spring-coiled pressure measuring device, but not the indicator diagram. [5]

Influenced
In 1837, Clapeyron’s memoir was translated into English and formed one of the papers presented in Volume I of William Taylor’s Scientific Memoirs. [6]

In 1844, James Joule, having read and digested the Taylor translation of Clapeyron, began to attack the "conservation of caloric" aspects of the theory, as follows:

“The principles I have adopted lead to a theory of the steam-engine very different from the one generally received, but at the same time much more accordant with facts. It is the opinion of many philosophers that the mechanical power of the steam-engine arises simply from the passage of heat from a hot to a cold body, no heat being necessarily lost during the transfer. This view has been adopted by Clapeyron in a very able theoretical paper, of which there is a translation in the Third part of Taylor's Scientific Memoirs. This philosopher agrees with Carnot in referring the power to vis viva developed by the caloric contained by the vapor in its passage from the temperature of the boiler to that of the condenser. I conceive that this theory, however ingenious, is opposed to the recognized principles of philosophy, because it leads to the conclusion that vis viva may be destroyed by an improper disposition of the apparatus.”
— James Joule (1844), “On the Changes of Temperature produced by the Rarefaction and Condensation of Air” (pg. 188)

In 1845, Carl Holtzmann, as described in his “On the Heat and Elasticity of Gases and Vapors”, had obtained a copy of Clapeyron, but was unable to find a copy of Carnot.

In 1848, William Thomson, in his "On an Absolute Thermometric Scale", said the following in respect to how he learned of Carnot via the 1837 English translation of Clapeyron's work:

“Carnot’s Theory of the Motive Power of Heat – Published in 1824 in a work entitled Réflexions sur la Puissance Motrice du Feu, by M. S. Carnot. Having never met with the original work, it is only through a paper by M. Clapeyron, on the same subject, published in the Journal de l’École Polytechnique, Vol. XIV, 1834, and translated in the first volume of Taylor’s Scientific Memoirs, that the Author has become acquainted with Carnot’s Theory.”
— William Thomson (1848), “On an Absolute Thermometric Scale” [4]

Thomson, before or after this point (see: Thomson's search for Carnot's Reflections), travelled around the Paris bookstores looking for a copy of Carnot's reflections, without success. Eventually, in Sep 1848, Thomson received a copy of Carnot's Reflections from colleague Professor Lewis Gordon.

On 2 Jan 1849, Thomson, having read Carnot’s Reflections, published, in ub Royal Society of Edinburgh, “An Account of Carnot’s Theory of the Motive Power of Heat”, in which the term "thermo-dynamic" was coined.

The discussions of Carnot, and the graphical summary of his work by Clapeyron, eventually reached the attention of German physicist Rudolf Clausius, in whose work thermodynamics was founded. [2]

Education
Clapeyron was a a former student of the École Polytechnique, whose interests were in the theory of structures and in civil engineering, generally.

Quotes | By
The following are quotes by Clapeyron:

“Dulong, in in his ‘Researches on the Specific Heats of Elastic Fluids’, established, by experiments, which are free from all objections, that equal volumes of all elastic fluids at a given temperature and pressure, compressed or expanded suddenly by a given fraction of their volumes, release or absorb the same absolute quantity of heat.”
— Emile Clapeyron (1834), “Memoir on the Motive Power of Heat” (pg. 73)

“It has been known for a long time that heat can develop ‘motive power’ [work] and, conversely, that by means of ‘motive power’ [work] heat can be produced.”
— Emile Clapeyron (1834), “Memoir on the Motive Power of Heat” (pg. 74); see: mechanical equivalent of heat

References
1. (a) Clapeyron, Émile. (1834). “Memoir on the Motive Power of Heat”, Journal de l’Ecole Polytechnique. XIV, 153 (and Poggendorff's Annalender Physick, LIX, [1843] 446, 566). Publisher.
(b) Clapeyron, Emile. (1837). “Memoir on the Motive Power of Fire” (pg. 347-58), Taylor’s Scientific Memoirs, Volume One.
2. Clausius, Rudolf. (1850). "On the Motive Power of Heat, and on the Laws Which can be Deduced From it for the Theory of Heat." Poggendorff's Annalen der Physik, LXXIX, 368, 500.
3. Cardwell, Donald S.L. (1971). From Watt to Clausius: the Rise of Thermodynamics in the Early Industrial Age (pgs. 220-22). Cornell University Press.
4. (a) H.H. (1822). “Account of a Steam-Engine Indicator”, Letter to the Editor of Quarterly Journal of Science, Literature and the Arts (Ѻ), 13:91-95. in: The Repertory of Arts and Manufactures (pgs. 14-19). Publisher, 1822.
(b) Cardwell, Donald S.L. (1971). From Watt to Clausius: the Rise of Thermodynamics in the Early Industrial Age (pg. 80). Cornell University Press.
4. Mander, Peter. (2012). “How Kelvin and Clausius discovered Carnot’s Ideas” (Ѻ), Carnot Cycle, WordPress.com, Aug 4.
5. (a) Pambour, Francois. (1834). Treatise on the Steam Locomotive (pg. 111; figure 23). Publisher, 1840.
(b) Cardwell, Donald S.L. (1971). From Watt to Clausius: the Rise of Thermodynamics in the Early Industrial Age (pg. 22#). Cornell University Press.
6. Clapeyron, Emile. (1837). “Memoir on the Motive Power of Fire” (pg. 347-58), Taylor’s Scientific Memoirs, Volume One.

External links
● Benoît Paul Émile Clapeyron – Wikipedia.
● Emile Clapeyron – MaxTutor Biographies, University of Saint Andrews, Scotland.