February 16, 1938, Pais was awarded two Bachelor of Science degrees in physics and mathematics, with minors in chemistry and astronomy. He began attending graduate courses in Amsterdam, including those in physics. He soon became disappointed by the only professor there in theoretical physics, (the son of the 1910 Nobel laureate Johannes Diderik van der Waals), whom he found dull and averse to the new developments in physics. Pais soon wrote to Uhlenbeck at Utrecht and was granted an interview. During the remainder of the spring term he discontinued attending classes in Amsterdam and made several trips to visit Uhlenbeck in his laboratory. 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 Anthony Kramers, 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. In the fall of 1939 Pais dedicated himself to preparing for his master's degree. Utrecht experimental physicist Leonard Salomon Ornstein provided him guidance in his independent physics studies. He was also influenced then by discussions with Léon Rosenfeld of the University of Liège, who was invited to Utrecht to give a colloquium in an effort to find a successor for Uhlenbeck and reported on the work he was then doing with Christian Møller on the meson theory of nuclear forces. Pais successfully passed the examination for his master's degree on April 22, 1940. On May 7 the Dutch minister of education appointed Rosenfeld to succeed Uhlenbeck at the University of Utrecht. On May 8 Pais wrote to Rosenfeld at Liège to ask if he might continue his studies under him if his appointment came through, and again on May 9 to congratulate him on his appointment. On May 10, 1940, the Germans invaded the