Second law of thermodynamics
The second law of thermodynamics may be expressed in many specific ways, the most prominent classical statements being the statement by Rudolf Clausius (1854), the statement by Lord Kelvin (1851), and the statement in axiomatic thermodynamics by Constantin Carathéodory (1909). These statements cast the law in general physical terms citing the impossibility of certain processes. The Clausius and the Kelvin statements have been shown to be equivalent.
Joseph Henry Keenan
In 1965, he published the classic textbook "Principles of General Thermodynamics" with George Hatsopoulos which was major turning point in thermodynamics since Gilbert N. Lewis and Merle Randall with their 1923 "Thermodynamics" textbook. Their now famous version of the second law of thermodynamics is: