 As already indicated, Feigl was a member of the Vienna Circle from its very beginning. Together with Friedrich Waismann he had suggested to Schlick the formation of an evening discussion group (see Feigl 1981, p. 60). Schlick took over the idea and installed a Thursday evening colloquium in the Vienna Boltzmanngasse 5, the location of the University’s Department of Mathematics. Among the co-founders of the Circle were, besides Waismann and Feigl himself, Hans Hahn, Otto Neurath, Olga Hahn-Neurath, Viktor Kraft, Felix Kaufmann, and the mathematician Kurt Reidemeister. It was the latter who proposed the reading and discussion of Ludwig Wittgenstein’s Tractatus logico-philosophicus. As Feigl reported in an unpublished interview,