Department of the Prussian Ministry of Science, Art and Public Education, and by 26 April he was head of the department. From 1 June 1934, he was a Ministerial Director and Chief of the Science Office at the Reich Ministry of Science, Education and Culture. Actually, the Science Office was split into two components, WI, a continuation of the Prussian department, and WII, the army office for research. Vahlen was head of WI, but, in actuality, the deputy chief, the chemist Franz Bachér ran WI. From this position, in 1936, Vahlen began publishing the journal Deutsche Mathematik, for which the Berlin mathematician Ludwig Bieberbach was the editor; in the journal, political articles preceded the scholarly articles. On 1 January 1937 Vahlen was relieved of his duties at the Ministry at his own request. Through a manipulation of the election process by Vahlen and his supporters, he was selected as president of the Prussian Academy of Sciences effective 1 January 1939 and remained in this post until 1 April 1943. In April 1944, Vahlen moved to Vienna after his Berlin apartment was destroyed in an air raid and again taught at the Technische Hochschule Wien. In August 1944 he moved to Prague and worked as a lecturer at the Charles University. At the end of the war in May 1945 he was imprisoned, and he died in Czech custody in November 1945. Mathematics Vahlen gained his doctorate with Beiträge zu einer additiven Zahlentheorie, and continued to specialise in number theory, but later turned to applied mathematics. Theodor Vahlen was an early proponent of geometric algebra. His 1902 paper in Mathematische Annalen recounts William Kingdon Clifford's construction of his 2n dimensional algebra with n − 1 anti-commuting square roots of −1. Vahlen also recounts split-biquaternions and parabolic biquaternions originated by Clifford. But Vahlen cites Eduard Study most of all since Study also focussed on the geometric motions (translation and rotation) as implicit in algebra. Since Vahlen explores some of the fractional-linear transformations of Clifford algebras, he is sometimes remembered for the Vahlen matrices. These are matrices with coefficients in a Clifford algebra that act on a projective line over a ring. In 1985 Lars Ahlfors recalled the article as follows: "The method was introduced as early as 1901 by K.T. Vahlen in a rather short, but remarkable, paper. His motivation was to unify the theory of motions in Euclidean, hyperbolic, and elliptic