Ehrenfest’s adiabatic theory and the old quantum theory, 1916–1918

I discuss in detail the contents of the adiabatic hypothesis, formulated by Ehrenfest in 1916. I focus especially on the paper he published in 1916 and 1917 in three different journals. I briefly review its precedents and thoroughly analyze its reception until 1918, including Burgers’s developments and Bohr’s assimilation of them into his own theory. I show that until 1918 the adiabatic hypothesis did not play an important role in the development of quantum theory. An erratum to this article can be found at