Braunschweig: Friedr. Wieweg & Sohn. 1913. First edition. "Two important heuristic principles have guided quantum physicists during the period 1913-1925, viz. Ehrenfest's Adiabatic Hypothesis and Bohr's Principle of Correspondence” (Sources of Quantum Mechanics). The hypothesis states that allowed quantum motions are transformed into allowed quantum motions when the parameters of the system (e.g, field strengths) are varied slowly and reversibly.
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).