BIOGRAPHIES 639 subjects. 1918, married Bridget Williams, with whom he had two children. 1919-1920, worked at Therma, a firm for the construction of electrical appa- ratuses of Schwanden, canton of Glarus. 1920, independent technical design- er in Schaffhausen, in laboratory in parents' home. 1927, purchased electro- technical factory in Schaffhausen. Held many patents, but in general achieved only sporadic commercial success. 1948, factory liquidated on his death. Sources: Communications from his children Grace M. Spitz-Habicht and John C. Habicht Ruedi 1961 obituary in Mitteilungen der Na- turforschenden Gesellschaft Schaffhausen 23 (1949/50): 301-307. Hopf, Ludwig b. 23 October 1884 in Nuremburg d. 21 December 1939 in Dublin Friend and collaborator of Einstein. Son of a hops merchant. 1902-1909, studied mathematical physics in Munich and Berlin. 1909, received doctorate from the University of Munich with Arnold Sommerfeld met Einstein at the 81st GDNA meeting in Salzburg 1910, in the summer semester, registered for Einstein's lectures on mechanics, kinetic theory of heat, and his physics seminar coauthored two papers with Einstein (Vol. 3, Docs. 7 and 8). 1911, summer semester, accompanied Einstein to Prague as Privatassistent. 1912, married Alice Goldschmidt, with whom he had five children. 1912-1922, ap- pointed Assistent at the Technical University in Aachen. 1914, Privatdozent in mechanics and theoretical physics there. 1914-1918, called into military service and served as a director in the aeronautics section of an airplane fac- tory in Berlin-Adlershof. 1919, worked as scientific consultant to the Mitt- leren Isar company of Munich and was guest lecturer at the Technical Uni- versity in Munich. 1920, returned to Aachen. 1921, appointed Extraordinary Professor of Applied Mathematics and Mechanics at the Technical University there. 1922, published standard work, Aerodynamik, with R. Fuchs. 1923, ap- pointed Ordinary Professor at same institution. 1931, published popular ex- position of "Relativity Theory." 1933, relieved of teaching and research du- ties visited Einstein a last time in Le Coq, Belgium. 1934, gave up his posi- tion in Aachen. 1939, received research grant at Cambridge University and was appointed lecturer at Trinity College, Dublin. Frequently accompanied Einstein on the piano at musical evenings in Zurich and Prague. Fascinated by psychoanalysis, he is said to have introduced Einstein to C. G. Jung in Zurich. Sources: Student Files, SzZU, Kassa-Archiv, letters of Alice Hopf to Carl Seelig, SzZE Bibliothek Sommerfeld and Seewald 1953.