In 1870 Clausius organized an ambulance corps in the Franco-Prussian War. He was wounded in battle, leaving him with a lasting disability. He was awarded the Iron Cross for his services.
His wife, Adelheid Rimpau died in 1875, leaving him to raise their six children. In 1886, he married Sophie Sack, and then had another child. Two years later, on 24 August 1888, he died in Bonn, Germany.[8]
Clausius's PhD thesis concerning the refraction of light proposed that we see a blue sky during the day, and various shades of red at sunrise and sunset (among other phenomena) due to reflection and refraction of light. Later, Lord Rayleigh would show that it was in fact due to the scattering of light.
His most famous paper, Ueber die bewegende Kraft der Wärme ("On the Moving Force of Heat and the Laws of Heat which may be Deduced Therefrom")[9]
was published in 1850, and dealt with the mechanical theory of heat. In this paper, he showed there was a contradiction between Carnot's principle and the concept of conservation of energy. Clausius restated the two laws of thermodynamics to overcome this contradiction. This paper made him famous among scientists. (The third law was developed by Walther Nernst, during the years 1906–1912).
Clausius's most famous statement of the second law of thermodynamics was published in German in 1854,[10] and in English in 1856.[11]
Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time.
During 1857, Clausius contributed to the field of kinetic theory after refining August Krönig's very simple gas-kinetic model to include translational, rotational and vibrational molecular motions. In this same work he introduced the concept of 'Mean free path' of a particle.[12][13][14]
In 1865, Clausius gave the first mathematical version of the concept of entropy, and also gave it its name.[8] Clausius chose the word because the meaning (from Greek ἐν en "in" and τροπή tropē "transformation") is "content transformative" or "transformation content" ("Verwandlungsinhalt").[4][15][16]
I prefer going to the ancient languages for the names of important scientific quantities, so that they may mean the same thing in all living tongues. I propose, accordingly, to call S the entropy of a body, after the Greek word 'transformation'. I have designedly coined the word entropy to be similar to 'energy', for these two quantities are so analogous in their physical significance, that an analogy of denomination seemed to me helpful.
— Rudolf Clausius, Ueber verschiedene für die Anwendung bequeme Formen der Hauptgleichungen der mechanischen Wärmetheorie
He used the now abandoned unit 'Clausius' (symbol: Cl) for entropy.[17]
The landmark 1865 paper in which he introduced the concept of entropy ends with the following summary of the first and second laws of thermodynamics:[4]
The energy of the universe is constant.
The entropy of the universe tends to a maximum.
Leon Cooper[16] added that in this way he succeeded in coining a word that meant the same thing to everybody: nothing.
^Dudenredaktion; Kleiner, Stefan; Knöbl, Ralf (2015) [First published 1962]. Das Aussprachewörterbuch [The Pronunciation Dictionary] (in German) (7th ed.). Berlin: Dudenverlag. pp. 280, 744. ISBN978-3-411-04067-4.
^Krech, Eva-Maria; Stock, Eberhard; Hirschfeld, Ursula; Anders, Lutz Christian (2009). Deutsches Aussprachewörterbuch [German Pronunciation Dictionary] (in German). Berlin: Walter de Gruyter. pp. 416, 884. ISBN978-3-11-018202-6.
^Cardwell, D.S.L. (1971), From Watt to Clausius: The Rise of Thermodynamics in the Early Industrial Age, London: Heinemann, ISBN978-0-435-54150-7
^ abCooper, Leon N. (1968). An Introduction to the Meaning and Structure of Physics. Harper. p. 331.
^Huang, Mei-Ling; Hung, Yung-Hsiang; Chen, Wei-Yu (2010-10-01). "Neural Network Classifier with Entropy Based Feature Selection on Breast Cancer Diagnosis". Journal of Medical Systems. 34 (5): 865–873. doi:10.1007/s10916-009-9301-x. ISSN1573-689X. PMID20703622. S2CID6658005.
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