Netherlands, Belgium, and Luxembourg, disrupting the mail between Utrecht and Liège for months. After mail service was restored, Pais again wrote to Rosenfeld in Liège. In the meantime Pais had been appointed as Rosenfeld's assistant — Kees van Lier, who had been Uhlenbeck's assistant and was to continue as such under Rosenfeld, had committed suicide following the German invasion. Rosenfeld approved of his appointment and arrived at Utrecht in September 1940 and Pais began working on his doctoral dissertation. Rosenfeld proposed that for his thesis Pais should formulate Rosenfeld and Møller's meson theory in terms of the five-dimensional space known as projective relativity theory, and then to use this theory to calculate the probability for the disintegration of deuterons when irradiated by energetic photons. Pais set to work studying projective relativity, meson theories, and nuclear physics related to the deuteron. In November 1940 the German authorities issued a decree banning Jews from all civil service positions, including academic posts. Pais therefore lost his assistant professorship, though Rosenfeld secretly arranged for his successor to unofficially share the responsibilities and salary of the position with Pais. Professor Leonard Ornstein, however, lost his directorship of and access to the laboratory and died a broken man on May 20, 1941. A subsequent German decree ordered that doctorate degrees could not be issued to Jews after June 14, 1941. Pais worked feverishly to complete his dissertation and meet other requirements for his doctorate. He obtained his doctoral degree in theoretical physics on June 9, just five days before the deadline. His was the last Ph.D. issued to a Dutch Jew until after the war. German occupation During his student years Pais had been involved in the Zionist movement, through which he became acquainted with Trusha (Tirtsah) van Amerongen and Tina (Tineke) Strobos, and developed a close friendship with these two women and their families. The Germans began to gradually restrict the activities of the Dutch Jews and in early 1942 required them to wear yellow stars. At first Pais felt safe because his former university status exempted him from being sent to a labor camp. In early 1943, however, the Dutch secretary general of internal affairs, Frederiks, made arrangements for the university Jews to report to Barneveld for their own safety, where they would be housed in a chateau. Pais did not trust that and instead went into hiding. Those who reported to Barneveld were