 Given the prominence of the topic today, it is surprising that we do not find the term in Philipp Frank’s account of the positivist discussion group in Vienna in the early twentieth century. However, Frank (1957) does speak of their perception of a “crisis” in modern physics caused by the undermining of classical mechanics by special relativity and quantum mechanics, and it was common to speak of this or that worldview or world picture (Weltanschauung, Weltbild), e.g., the electromagnetic vs. the Einsteinian vs. the mechanical picture. Nor do we find talk of scientific revolutions in the later Vienna Circle, even after the diaspora following the rise of Hitler. The technical term does not appear in Karl Popper’s Logik der Forschung (1934) nor in his 1959 English expansion of that work as The Logic of Scientific Discovery, at least not important enough to be indexed. Hans Reichenbach (1951) speaks rather casually of the revolutions in physics. The technical term is not in Ernest Nagel’s The Structure of Science (1961). Nor is it in Stephen Pepper’s World Hypotheses (1942). It plays no significant role in N. R. Hanson’s Patterns in Discovery (1958), despite its talk of the theory-ladenness of observation and perceptual Gestalt switches. Meanwhile, there were, of course, a few widely-read works in the background that spoke of major ontological changes associated with the rise of modern science, especially E. A. Burtt’s Metaphysical Foundations of Modern Physical Science (1924). Burtt’s book influenced Koyré, who, in turn, influenced Kuhn.