On January 2, 1822, German physicist and mathematician Rudolf Julius Emanuel Clausius was born. He is considered one of the central founders of the science of thermodynamics, who introduced the concept of entropy in 1865.
Rudolf Clausius’ father founded a school and became its Principal. However, Rudolf Clausius moved to Stettin (now Szczecin, Poland), where he attended a grammar school. He entered the University of Berlin around 1840, being mostly interested in history but he decided to focus on mathematics and physics. It is believed that around 1847, Clausius submitted his dissertation on the problem of reflected light in the sky, to Halle University. His first work on the mechanical theory of heat was titled “Über die bewegende Kraft der Wärme” and was published in 1850 and it is probably his most important and most influential work. Fortunately for Clausius, the paper’s importance was noticed quickly and he was invited to the post of Professor at the Royal Artillery and Engineering School at Berlin in the same year. [1,2]
The theory of heat that existed at the time was called the caloric theory and was based on the axioms that the heat in the universe conserved and that the heat in a substance is a function of the state of the substance. Clausius however, stated in his 1850 paper, that these assumptions were false and he gave two laws of thermodynamics to replace the incorrect assumptions. His explanations included the nature of free heat and latent heat. In the First Law of Thermodynamics it was already proven that both axioms of the caloric theory are false. The paper also contained a version of the Second Laws of Thermodynamics and he kept working on the law for the next 15 years, trying to put the law into a simpler form. In his work, Rudolf Clausius mentioned Sadi Carnot‘s principle of the efficiency of heat engines. The Clausius-Clapeyron equation appears which expresses the relation between the pressure and temperature at which two phases of a substance are in equilibrium. In his famous paper, Clausius understood entropy as the quantity that remains invariant during changes of volume and temperature in a Carnot cycle. However, he did not name this concept back then. He described the concept for the first time in 1865 more clearly and he stated and described the First and Second laws of thermodynamics: 1st: The energy of the universe is constant, and 2nd: The entropy of the universe tends to a maximum.
Following his investigations and his published works, Clausius faced several disputes with especially Thompson and Tait on the discovery of the theory of heat and its real origin. Many historians believe that Clausius made more use of the works and thoughts of others than he might have admitted. However, his great contribution to physics remains the idea of the irreversible increase in entropy. 
Rudolf Clausius became professor of physics at the Polytechnikum in Zurich in 1855 and made contributions to the theory of electrolysis. Clausius became professor of physics in Würzburg in 1867 and Bonn two years later. He was elected a Fellow of the Royal Society of London in 1868 and received its Copley Medal in 1879. He also received the Huygens Medal in 1870, the Poncelet Prize in 1883. [1,2]
At yovisto, you may learn more about ‘The Flow of Heat‘ by Rick Prellinger.
References and Further Reading:
-  Rudolf Clausius Biography at Mac Tutor History
-  Rudolf Clausius at Britannica
-  Rudolph Clausius at zbMATH
-  Rudolph Clausius at Mathematics Genealogy Project
-  Rudolph Clausius at Wikidata
-  Timeline for Rudolph Clausius, via Wikidata
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