In thermodynamics, Rudolf Clausius (1822-1888) was a German physicist noted for being the central founder of thermodynamics.

“The work of Clausius lies not on the shelves of libraries, but in the thoughts of men, and in the history of more than one science.”

– Willard Gibbs (1889), American engineer [7]

Clausius founded thermodynamics through the publication of his nine memoirs on the mechanical theory of heat (1850-1865), as contained in his 1865 textbook The Mechanical Theory of Heat (Mechanische Wärmetheorie); the first of which being his 1850 article “On the Moving Force of Heat and the Laws of Heat which may be Deduced Therefrom”, in which he grouped and refined the earlier work of French physicist Sadi Carnot (Reflections on the Motive Power of Fire, 1824) on the assumed reversibility of the working body together with the mechanical equivalent of heat measurements of English physicist James Joule ("On the Mechanical Equivalent of Heat", 1845), in the development of the conservation of energy, thus framing the outline of what he called the second main principle and first main principle (second law and first law of thermodynamics), respectively, in equation format, later encapsulated in the form of the ten fundamental equations of thermodynamics, as indicated by roman numerals in the second edition (1875) of his textbook. [1]

Original English translation of the famous April 24, 1865 statement of the two laws of the universe by Clausius. [4]

In short, Clausius' 1875 textbook is the definitive textbook of thermodynamics, upon which all branches of thermodynamics are built.

Overview
In Clausius' nine memoirs, through the development of his conception of quantity entropy, symbol S, and its relation to irreversibility in engine cycles, Clausius pulled together a number of philosophical cornerstones, such as time, heat, friction, chemistry, transformation, spontaneity, conservation and others, into one cohesive theory namely the first and second laws of thermodynamics, otherwise known as the "dynamical theory of heat".

The paper that spurred Clausius on in his quest to formulated laws on the relationship between heat and work was French physicist Sadi Carnot's 1824 publication "Reflections on the Motive Power of Fire". The sentence of Carnot's paper that caught the direct attention of Clausius is, in Clausius' own words, that: [2]

“Whenever work is done by heat (on a body in a cycle) no permanent change occurs in the condition of the working body [and that to deny this] would overthrow the whole theory of heat, of which it is the foundation.”

In this statement, in particular, according to Clausius, that a change does occur in the condition of the working body, Clausius saw his life's work before him.

Clausius in his younger days, possibly 20s or 30s.

The collected papers of Clausius, constituting two volumes, total 16 papers: 1-9 (1850-65) on thermodynamics, 10-13 (1852-57) on the theory of electricity, and 14-16 (1857-62) are on gas theory. [3]

In his 1857 article “On the Nature of Heat Compared with Light and Sound”, Clausius compared heat, light, and sound to give a Boltzmann-Ebeling like description of the earth ecosystem based on metabolic needs, insulation, and chemical affinities. [12]

Kinetic theory
In 1857, Clausius published his "On the Nature of the Movement which we call Heat", in which, according to his own words independently of German chemist and physicist August Krönig, and his 1856 "A General Theory of Gases", developed a similar, but much more sophisticated version of the theory which included translational and contrary to Krönig also rotational and vibrational molecular motions. [6] In a followup 1858 paper, Clausius he introduced the concept of mean free path of a particle.

Education
Clausius’ early education was at a small private school, where his father was the principle. Following private schooling, Clausius moved on to the Gymnasium in Stettin. In 1840, at the age of 18, Clausius entered the University of Berlin in which he first entertained thoughts of a degree in history, but eventually settled on a degree in mathematics and physics, completed in 1844. He then spent a probationary year at the Frederic-Werder Gymnasium teaching advanced classes in mathematical physics.


Clausius completed his PhD dissertation in 1847 (or 1848), entitled On those Atmospheric Particles that Reflect Light (De iis Atmosphaere Particulis quibus lumen Reflectituri), under German mathematician and physical chemist Johann Schweigger, which proposed an explanation for the blue color of the sky, the red colors seen at sunrise and sunset, and the polarization of light, at the University of Halle (Martin-Luther-Universität Halle-Wittenberg). [5]

in 1850 was appointed professor of physics in the royal artillery and engineering school at Berlin. Late in the same year he delivered his inaugural lecture as Privatdocent in the university. [11]

In 1855, Clausius became a physics professor at the Polytechnic School in Zurich and two years later, in 1857, he was appointed to the same position in the University of Zurich. In 1867 he moved to Würzburg as professor of physics. [11] In 1869, he became a physics professor at the University of Bonn, where he remained until his dereaction (death) in 1888. [9]

American physicist Michael Guillen gives a fairly detailed biographical overview of Clausius in chapter "Unprofitably Experience" on the second law in his 1995 book Five Equations that Changed the World. [10]

Social mechanics

See also: Leon Winiarski

In circa 1880, Clausius gave a talk on “On the Energy Supplies of Nature and the Utilization of them for the Benefit of Mankind” (published in book form in 1885), which, according to Spanish applied mathematics historian Jose Pacheco, was said to have inspired Austrian science teacher Eduard Sacher to write his 1881 book Outline of a Mechanics of Society. [8]

References
1. (a) Clausius, R. (1865). The Mechanical Theory of Heat – with its Applications to the Steam Engine and to Physical Properties of Bodies (trans. Thomas Hirst, 1867). (URL) London: John van Voorst.
(b) Clausius, Rudolf. (1875). The Mechanical Theory of Heat (trans. Walter Browne, 1979) London: Macmillan & Co.
2. Clausius, Rudolf. (1850). “On the Moving Force of Heat and the Laws of Heat which may be Deduced Therefrom”, Communicated to the Academy of Berlin, Feb.; Published in Poggendorff’s Annalen, March-April, Vol. lxxix, pgs. 368, 500, and Translated in the Philosophical Magazine, July 1851, Vol. ii. pgs. 1, 102.
3. “Theory of Electricity by Rudolf Clausius in the Development of Thermodynamics” – by Eri Yagi and Rika Tadokoro.
4. Clausius, Rudolf. (1865). "On Several Convenient Forms of the Fundamental Equations of the Mechanical Theory of Heat" (ninth memoir), Read at the Philosophical Society of Zurich on the 24th of April, 1865; published in the Vierteljahrsschrift of this society, Bd. x. S. 1.; Pogg. Ann. July, 1865, Bd. cxxv. S. 353; Journ. de Liouville, 2e ser. t. x. p. 361; The Mechanical Theory of Heat, ch. 9 (pg. 365). J. Van Voorst, 1867.
5. (a) Cropper, William H. (2001). Great Physicists: the Life and Times of Leading Physicists from Galileo to Hawking (pgs. 104-05). Oxford University Press.
(b) Rudolf Clausius – Mathematics Genealogy Project.
(c) Johann Schweigger – Wikipedia.
6. Clausius, R. (1857), "Über die Art der Bewegung, die wir Wärme nennen" (About the Nature of the Movement, Which we call Heat), Annalen der Physik 100: 353-379.

Online table of contents to Clausius 1875 textbook The Mechanical Theory of Heat.

7. (a) Gibbs, Willard. (1889). “Rudolf Julius Emanuel Clausius”, Proceedings of the American Academy, New Series, Vol. XVI, pgs. 458-65; in: Scientific Papers of J. Willard Gibbs: Dynamics and Vector Analysis, pgs. 261-67.
(b) Pickover, Clifford A. (2008). Archimedes to Hawking (pg. 339). Oxford University Press.
8. (a) Pacheco, Jose M. (2008). “Does More Abstraction Imply Better Understanding: Ampuntes de Mecanica Social by Antonio Porunondo). Max Planck Institute for the History of Science, Preprint 351.
(b) Clausius, Rudolf. (1885). Über die Energievorräthe der Natur und ihre Verwerthung zun Nutzen der Menschheit (On the Energy Supplies of Nature and the Utilization of them for the Benefit of Mankind). Bonn: Verlag von Max Cohen & Sohn.
9. Magie, W.F. (1899). “Biographical Sketch of Clausius”, in: The Second Law of Thermodynamics: Memoirs by Carnot, Clausius, and Thomson (pgs. 107-108). Harper & Brothers.
10. Guillen, Michael. (1995). Five Equations that Changed the World (ch.: An Unprofitable Experience: Rudolf Clausius and the Second Law of Thermodynamics, pgs. 165-214). Hyperion.
11. Rudolf Clausius – Encyclopedia Britannica (1911).
12. Clausius, Rudolf. (1857). “On the Nature of Heat Compared with Light and Sound” (“Ueber das Wesen der Wärme verglichen mit Licht und Schall”). Zurich: Verlag von Meyer & Zeller.

Further reading
● Clausius, Rudolf. (1857). On the Kind of Motion we Call Heat (Über die Art der Bewegung welche wir Wärme nennen). Publisher.
● Clausius, Rudolf. (1858). “On the Treatment of Differential Equations which are not Directly Integrable” (Mathematical Introduction, Mechanical Theory of Heat, 1865). Original from note published in Dingler’s Polytechnisches Journal, Vol. cl. pg. 29.
● Clausius, Rudolf. (1859). “The Potential and the Potential Function”, Leipzig: John Ambrose Barth.
● Clausius, Ludwig. (1878). “On the Relation of the Work Performed by Diffusion to the Second Proposition of the Mechanical Theory of Heat.” Philosophical Magazine: a Journal of Theoretical, Experimental and Applied Physics, 5(26): pgs. 237-38. Jul-Dec.
● Riecke, name. (1889). Rudolf Clausius (biography). Gottingen.
● Rudolf Clausius – The New International Encyclopedia, 1902.
● Daub, Edward E. (1966). Rudolf Clausius and the Nineteenth Century Theory of Heat. University of Wisconsin.
● Kirkham, M.B. (2005). Principles of Soil and Plant Water Relations (XI. Appendix: Biography of Rudolf Clausius, pg. 311). Academic Press.
● Wolff, Stefan L. (2012). “Rudolf Clausius: A Pioneer of Modern Theory of Heat” (abs), Vacuum, Mar 01.

External links
● Rudolf Clausius – Wikipedia.
● Rudolf Clausius – MacTutor Biographies, University of St Andrews.
● Rudolf Clausius – NNDB.com.
● Rudolf Clausius – Eric Weisstein’s World of Scientific Biography.
● Clausius T-shirt - Photo (and his famous enunciation of the two laws).
● Clausius Tower Society - Koszalin University of Technology.