Editing Rudolf Clausius (section)

===Entropy===
{{Main|History of entropy}}{{See also|History of thermodynamics#Rudolf Clausius}}
In 1865, Clausius gave the first mathematical version of the concept of [[entropy]], and also gave it its name.<ref name="Cropper2004"/>  Clausius chose the word because the meaning (from [[Ancient Greek|Greek]] ἐν ''en'' "in" and τροπή ''tropē'' "transformation") is "''content transformative''" or "''transformation content''" ("''Verwandlungsinhalt''").<ref name="Theory of Heat">{{cite book|last=Clausius|first=R.|title=The Mechanical Theory of Heat – with its Applications to the Steam Engine and to Physical Properties of Bodies|year=1867|publisher=John van Voorst|location=London|url=https://archive.org/details/mechanicaltheor04claugoog|quote=editions:PwR_Sbkwa8IC.|access-date=19 June 2012}} Contains English translations of many of his other works.</ref><ref>{{Citation  | author=Clausius, R.  | title =Ueber verschiedene für die Anwendung bequeme Formen der Hauptgleichungen der mechanischen Wärmetheorie | url =http://gallica.bnf.fr/ark:/12148/bpt6k152107/f369.table  | journal =Annalen der Physik  | volume =125 | issue =7 | pages =353–400 | year =1865 |doi=10.1002/andp.18652010702|bibcode = 1865AnP...201..353C }}</ref><ref name="Cooper">{{cite book|last1=Cooper|first1=Leon N.|title=An Introduction to the Meaning and Structure of Physics|date=1968|publisher=Harper|page=331}}</ref>{{Blockquote|text=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.|author=Rudolf Clausius|title=Ueber verschiedene für die Anwendung bequeme Formen der Hauptgleichungen der mechanischen Wärmetheorie}}He used the now abandoned unit 'Clausius' (symbol: '''Cl''') for entropy.<ref>{{Cite journal|last1=Huang|first1=Mei-Ling|last2=Hung|first2=Yung-Hsiang|last3=Chen|first3=Wei-Yu|date=2010-10-01|title=Neural Network Classifier with Entropy Based Feature Selection on Breast Cancer Diagnosis|journal=Journal of Medical Systems|language=en|volume=34|issue=5|pages=865–873|doi=10.1007/s10916-009-9301-x|pmid=20703622|s2cid=6658005|issn=1573-689X}}</ref>
:1 Clausius (Cl) = 1 [[calorie]]/[[degree Celsius]] (cal/°C) = 4.1868 [[joule]]s per [[kelvin]] (J/K)

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:<ref name="Theory of Heat" />
{{blockquote |The energy of the universe is constant.<br />
The entropy of the universe tends to a maximum.}}

[[Leon Cooper]]<ref name="Cooper" /> added that in this way he succeeded in coining a word that meant the same thing to everybody: nothing.