 1919 saw the publication of Bergson’s Mind Energy, a collection of essays concerned with metaphysical and psychological problems. During the same year he retired from his teaching duties. However, in 1922, Bergson was appointed president of the International Commission for Intellectual Cooperation — the precursor to UNESCO. There, Bergson participated in a debate with Einstein, which, according to Merleau-Ponty, seems to testify to a “crisis of reason.”  Bergson published his reflections on Einstein as Duration and Simultaneity (see Mélanges, 1972). There is some controversy surrounding this book. Bergson allowed the book to be reprinted up to the sixth edition in 1931. However Édouard Le Roy claims in a letter from 1953 (well after Bergson’s death) that he often spoke with Bergson about relativity. Le Roy says, “[Bergson] added with insistence that the defective state of his knowledge of mathematics did not allow him to follow the development of generalized relativity in the detail such a development required. Consequently [Bergson] thought it wiser to let the question drop. This is why he refused to let Duration and Simultaneity be reprinted” (Avertissement pour la septième edition, Durée et simultanéité, p. 5, [Lawlor translation]). However, in Bergson’s will, he does not mention Duration and Simultaneity as a text not to be republished. Thus, the editors of the seventh edition in 1968 (Jean Wahl, Henri Gouhier, Jean Gutton, Vladimir Jankélévitch) saw fit to reprint this book. In a letter from November 1924, after complaining that in general his writings on relativity had been badly understood by the “relativist physicists.” Bergson clarifies that his writings on relativity should not be seen as dismissive of relativity theory. He says, “For my part, I think that the theory of relativity represents a very great advance, not only from the viewpoint of physics, but also from the viewpoint of philosophy” (Bergson, Correspondences, p. 1122 [Lawlor translation]). If Deleuze’s interpretation is correct, the confrontation that Duration and Simultaneity develops is not one between Bergson and Einstein but a confrontation between Bergson’s interpretation of multiplicities and Riemann’s interpretation of multiplicity, Riemann’s interpretation being, according to Deleuze, the basis of Einstein’s theory (Deleuze, 1991, pp. 39–40, and also see below, “The Concept of Multiplicity”).