 According to its unofficial manifesto (see section 2.3 below), the Circle had “members” and recognized others as “sympathetic” to its aims. It included as members, besides Schlick who had been appointed to Mach’s old chair in Philosophy of the Inductive Sciences at the University of Vienna in 1922, the mathematician Hans Hahn, the physicist Philipp Frank, the social scientist Otto Neurath, his wife, the mathematician Olga Hahn-Neurath, the philosopher Viktor Kraft, the mathematicians Theodor Radacovic and Gustav Bergmann and, since 1926, the philosopher and logician Rudolf Carnap. (Even before World War I, there existed a similarly oriented discussion circle that included Frank, Hahn and Neurath. During the time of the Schlick Circle, Frank resided in Prague throughout, Carnap did so from 1931.) Further members were recruited among Schlick’s students, like Friedrich Waismann, Herbert Feigl and Marcel Natkin, others were recruited among Hahn’s students, like Karl Menger and Kurt Gödel. Though listed as members in the manifesto, Menger and Kraft later wanted to be known only as as sympathetic associates, like, all along, the mathematician Kurt Reidemeister and the philosopher and historian of science Edgar Zilsel. (Karl Popper was never a member or associate of the Circle, though he studied with Hahn in the 1920s and in the early 1930s discussed its doctrines with Feigl and Carnap.) Over the years, other participants (not listed in the manifesto) included other students of Schlick’s and Hahn’s like Bela von Juhos, Josef Schächter, Walter Hollitscher, Heinrich Neider, Rose Rand, Josef Rauscher and Käthe Steinhardt, a secondary teacher, Robert Neumann, and, as notable thinkers with independent connections, the jurist and philosopher Felix Kaufmann (also a member of F.A. von Hayek’s “Geistkreis”) and the innovative psychologist Egon Brunswik (coming, like the even more loosely associated sociologists Paul Lazarsfeld and Marie Jahoda, from the pioneering Karl Bühler’s University Institute of Psychology).