In the autumn of 1928, Oppenheimer visited Paul Ehrenfest's institute at the University of Leiden, the Netherlands, where he impressed by giving lectures in Dutch, despite having little experience with the language.
No outono de 1928 Oppenheimer visitou o instituto de Paul Ehrenfest na Universidade de Leiden, nos Países Baixos, onde impresionou os locais ó impartir unhas charlas en neerlandés malia ter moi pouca práctica nesta lingua.