Braunschweig: Friedr. Wieweg & Sohn. 1913.
The paper in which he first formulated his 'Adiabatic Hypothesis' of quantum theory. "Two important heuristic principles have guided quantum physicists during the period 1913-1925, viz. Ehrenfest's Adiabatic Hypothesis and Bohr's Principle of Correnspondance. The Adiabatic Hypothesis, first formulated by Ehrenfest in 1913 [this paper], says: If a system be affected in a reversible adiabatic way, allawed motions are transformed into allowed motions." (Van der Waerden: Sources of Quantum Mechanics, pp.3-4).
Published in: Verhandlungen der Deutschen Physikalischen Gesellschaft im Jahre 1913, Nr. 11, pp.451-457. Entire issue offered. Original printed wrappers; faint rubber stamp to front wrapper, otherwise very fine. 8vo (228 x 152 mm).