 However, the reading of Wittgenstein’s Tractatus was only one of a number of topics discussed within the Circle. According to Feigl, “about 60 % of our time was devoted to the problems of the foundation of mathematics and the rest to philosophy of science and epistemology” (ibid.). Between 1926 and 1928 it was the reading of (the typescript of) Rudolf Carnap’s Der logische Aufbau der Welt which dominated the discussion.