WE are grateful to Herbert S. Bailey, Jr., Director of Princeton University Press, for the personal interest he has shown in this book from the time of its conception. His enthusiasm, encouragement, and advice lightened the way to its completion.
Our thanks go, also, to Sonja Bargmann, who subjected the translations to a searching scrutiny, not merely correcting errors but also making major improvements in the wording. We are grateful, too, to Gail Filion for her perceptive suggestions and editorial wisdom.
We thank: Mrs. Marianne Dreyfuss for permission to quote from a letter written by her grandfather Leo Baeck; L. F. Haber for permission to quote from a letter written by Fritz Haber; Elmar Lanczos for permission to quote from a letter written by Cornelius Lanczos; Theodor von Laue for permission to quote from a letter written by Max von Laue; J. Peemans, Chef-Adjoint du Cabinet du Roi, for permission to quote a poem written by the late Queen Elizabeth of Belgium; and, of course, Otto Nathan for permission to quote voluminously from writings of Einstein, and also for his lively interest in our book.