  In 1913 Weyl was offered, and accepted, a professorship at the  Eidgenössische Technische Hochschule—ETH (Swiss Federal  Institute of Technology)—in Zürich. Weyl’s years in  Zürich were extraordinarily productive and resulted in some of  his finest work, especially in the foundations of mathematics and  physics. When he arrived in Zürich in the fall of 1913, Einstein and Grossmann were struggling to overcome a difficulty in their  effort to provide a coherent mathematical formulation of the general  theory of relativity. Like Hilbert, Weyl appreciated the importance  of a close relationship between mathematics and physics. It was  therefore only natural that Weyl should become interested in  Einstein’s theory and the potential mathematical challenges it might  offer. Following the outbreak of the First World War, however, in May 1915 Weyl was called up for military service. But Weyl’s academic  career was interrupted only briefly, since in 1916 he was exempted  from military duties for reasons of health. In the meantime Einstein  had accepted an offer from Berlin and had left Zürich in 1914.  Einstein’s departure had weakened the theoretical physics program at  the ETH and (as reported by Frei and Stammbach (1992, 26) the  administration hoped that Weyl’s presence would alleviate the  situation. But Weyl needed no external prompting to work in, and to  teach, theoretical physics: his interest in the subject in general  and, above all, in the theory of relativity, gave him more than  sufficient motivation in that regard. Weyl decided to lecture on the  general theory of relativity in the summer semester of 1917, and  these lectures became the basis of his famous book  Raum-Zeit-Materie (Space-Time-Matter) of 1918.