If we do not count The Mind Energy (L"Energie spirituelle) which was a mere collection of lectures and articles previously published, Duration and Simultaneity, published in 1922, is the fifth book of Bergson, — the first one published after Creative Evolution. The second edition in 1923, with a new preface and three appendices, was incorporated in the texts published by André Robinet in 1968 under the title Mélanges. Henri Gouhier in his introduction to this book stated the reasons why Duration and Simultaneity was included in it because Bergson's attitude toward the relativity theory remained unchanged; in other words, that the book remains an authentic part of his thought. This becomes quite clear when we re-read a long footnote on this subject in his last book La pensée et le mouvant.¹ Bergson at the end of his life, in a conversation with Edouard Le Roy, expressed some doubts about a new re-printing of his D.S. since he — according to the same witness — viewed it as incomplete rather than erroneous because in it the general theory of relativity had been hardly dealt with.²