We are pleased to be publishing this translation of selected documents of Volume 15 of The Collected Papers of Albert Einstein, the companion volume to the annotated, original-language documentary edition. As we have stated in all earlier volumes, these translations are not intended for use without the documentary edition, which provides the extensive editorial commentary necessary for a full historical and scientific understanding of the source documents. The translations strive first for accuracy, then literariness, though we hope that both have been achieved. The documents were selected for translation by the editors of The Collected Papers of Albert Einstein. We thank Jennifer Nollar James for organizing all aspects of the translation project and for her careful editing and revisions Ann M. Hentschel, Mary Jane Teague, Andreas Aebi, and Klaus Hentschel for their dedication in making Einstein’s writings and correspondence available to the English-speaking world Diana Kormos Buchwald for her revisions A. J. Kox, Dennis Lehmkuhl, Jeremy Schneider, and Melissa Büttner for assisting with the translation. József Illy typeset equations, and Emily de Aráujo took care of image processing. Diana Kormos Buchwald produced camera-ready copy in collaboration with A. J. Kox, Rudy Hirschmann, and Terri O’Prey. Many thanks to Alice Calaprice and Beth Gianfagna for their careful copyediting and proofreading of the manuscript. Finally, we are most grateful to the National Endowment for the Humanities, Grant RQ-50620-12, and to the National Science Foundation, Grant No. SES-1555639, for their support of our project. Princeton University Press December 2017 PUBLISHER’S FOREWORD