[2] From 1949 to 1966, Klein was a member of the staff of the physics department of Cleveland's Case Institute of Technology, starting as an instructor and becoming a full professor in 1960.
During this time, Klein contributed to the Theoretical Physics Department at the Dublin Institute for Advanced Studies.
[2] In the 1960s Martin extended his historical range and published a series of seminal papers by Max Planck and Einstein on the foundation of quantum theory.
He also translated into English and published letters on wave mechanics by Einstein, Schrödinger, Planck, and Hendrik Lorentz.
Martin later turned to the investigation of the foundations of thermodynamics and statistical mechanics in the 19th century, writing important papers on Ludwig Boltzmann, Sadi Carnot, Rudolf Clausius, J. Willard Gibbs, and James Clerk Maxwell.