xliv ACKNOWLEDGMENTS The cooperation of Prof. Don Howard and Dr. Anne Kox has proved of inestimable value in assembling and annotating the materials in this volume. We are sincerely grateful. We also thank Gabriele Block, Rosemarie Davis, Dr. Jean Eisenstaedt, Gary Goethals, Edith Laznovsky, Richard Newton, Dulce Nordlund, Dr. Fritz and Grete Schulmann, Linda Sheldon, Deborah and Evelyn Stachel, Magda Tisza, Dr. Von Underwood, and Elsa Zanini for their help at various stages of the volume's preparation. We are grateful to the members of the Editorial Advisory Board, listed in the front matter, for advice on general policy questions and on earlier drafts of this volume. The late Prof. Banesh Hoffmann, Prof. Aryeh Dvoretzky, Prof. Yehuda Elkana, Prof. Gerald Holton, and Prof. Reuven Yaron provided writ- ten comments on earlier drafts. The members of our Editorial Committee worked very closely with us on a number of questions of editorial policy, helped us make many decisions about this volume, and provided detailed comments on several drafts. We thank Profs. Peter G. Bergmann, Robert S. Cohen, Martin J. Klein, Abraham Pais, Nathan Reingold, and Fritz Stern for their advice and encouragement. We also thank Dr. Paul Forman, Prof. Jürg Fröhlich, Dr. Beat Glaus, Prof. Peter Havas, Prof. Walter Hunziker, Prof. Res Jost, Dr. Christa Kirsten, Prof. Russell McCormmach, Prof. Horst Melcher, and Dr. Helmut Rechenberg for valuable comments on earlier drafts. Without the perseverance of Herbert S. Bailey, Jr., former Director of Princeton University Press, our editorial project would never have been undertaken, nor would this edition have been realized. His patience and concern were a welcome support in difficult times. The new Director, Walter Lippincott, has provided continuing support. Alice Calaprice, Senior Editor, and Jan Lilly, Head of the Design Department, have been very helpful in the preparation of the typescript for publication. We thank them as well as the production staff of the Press. We join the publisher in thanking the private foundations, government agencies, and individual benefactors listed in the Publisher's Foreword whose financial support make this project possible. We especially thank Prof. Res Jost, our liaison with Swiss foundations Dr. Ronald J. Overmann, Program Director for History and Philosophy of Science of the National Science Foun- dation and Dr. Helen C. Aguera, former Program Officer, Research Materials Program, and Dr. Margo Backus, Assistant Director, Texts, Division of Research Programs of the National Endowment for the Humanities, for their interest in and encouragement of our work.