Dirk van Delft, Einstein in Leiden, Physics Today 59 (April 2006) 57-26. The frontpage shows a painting by Marijke Kamerlingh Onnes, niece of Heike. H.B.G. Casimir, S.A. Goudsmit. . Niels Bohr, 1949, "Discussion With Einstein on Epistemological Problems in Atomic Physics " in Schilpp, P. A., ed., , The Library of Living Philosophers. Northwestern Univ. Press: 200-41. Albert Einstein, 1950. . Martin J. Klein, 1970. . Amsterdam. --------, 1981, Not by Discoveries Alone: the Centennial of Paul Ehrenfest, : 3-14. Kramers, H. A., 1933, : 273-276. --------, 1933, : 667. Navarro, L.; Pérez, E., 2006, "Paul Ehrenfest: the genesis of the adiabatic hypothesis, 1911-1914. ". : 209-267. Wolfgang Pauli, 1933, : 841-843. --------, 1935, "Physiker als Stilisten", : 297-301. G. E. Uhlenbeck, 1956, "Reminencences of Professor Paul Ehrenfest", : 431-433.