In the fall of 1938 Pais enrolled for graduate classes at University of Utrecht. Uhlenbeck, however, spent that term as a visiting professor at Columbia University in New York City. He left Pais with the use of his laboratory and a list of topics to study and work on. Pais was soon exposed to other prominent Dutch physicists and areas of research in experimental physics. He became well-acquainted with Hendrik Casimir, a physics professor at Leiden University who lectured at Utrecht twice a week on quantum physics. When Uhlenbeck returned from America, he brought news of a meeting he had attended in Washington, D.C., in which Niels Bohr and Enrico Fermi had first made public their news about nuclear fission. Uhlenbeck also announced that he would be leaving in the summer of 1939 for a professorship at University of Michigan, Ann Arbor.