John Werner Cahn (January 9, 1928 – March 14, 2016) was an American scientist and recipient of the 1998 National Medal of Science. Born in Cologne, Weimar Germany, he was a professor in the department of metallurgy at the Massachusetts Institute of Technology (MIT) from 1964 to 1978. From 1977, he held a position at the National Institute of Standards and Technology (formerly the National Bureau of Standards). Cahn had a profound influence on the course of materials research during his career. One of the foremost authorities on thermodynamics, Cahn applied the basic laws of thermodynamics to describe and predict a wide range of physical phenomena. Biography Hans Werner Cahn was born in Cologne, Germany, to a Jewish family. His father was an anti-Nazi lawyer and his mother an X-ray technician. After the Machtergreifung in 1933, the elder Cahn escaped arrest only because he had been forewarned by a fellow lawyer. The family fled Germany and eventually ended up in Amsterdam. They immigrated to America in 1939, where Hans became John. Most of his family back in Europe was murdered in the Holocaust. The Cahns settled in New York City. John Cahn became an American citizen in 1945. Serving in the United States Army, he was stationed in Japan during its occupation by the Allies. Cahn received a bachelor's degree in chemistry in 1949 from the University of Michigan. He later earned a Ph.D in physical chemistry in 1953 from the University of California at Berkeley. His doctoral thesis was titled "The Oxidation of Isotopically Labelled Hydrazine" and his thesis advisor was R. E. Powell. In 1954, Cahn joined the chemical metallurgy research effort at the General Electric laboratory in Schenectady, New York, led by David Turnbull. Turnbull had done pioneering work on the kinetics of nucleation, and there was a focus in the group on understanding the thermodynamics and kinetics of phase transformations in solids. In 1964, Cahn became a professor in the Department of Metallurgy (now Materials Science) at the Massachusetts Institute of Technology. He left MIT in 1978. In 1969, Cahn began a long professional relationship with his graduate student, Francis Larché, whose work focussed on the effect of mechanical stress on the thermodynamics of solids. The Larche–Cahn approach is the cornerstone of the treatment of the thermodynamics of stressed materials. Good examples of this phenomenon are the regions near a coherent precipitate or the stress field