NOTE ON THE TRANSLATION A translation of The Collected Papers of Albert Einstein is being published by Princeton University Press, under the supervision of Diana Kormos Buchwald, General Editor. Volume 13, containing translations of selected texts, was prepared by Ann Hentschel, translator. Klaus Hentschel was the consultant, and Alice Cala- price was the copy editor. At the Einstein Papers Project, Rosy Meiron and Jennifer Nollar James assisted in perfecting the translation. Osik Moses prepared the index, typeset and finalized the volume, and, together with Rudy Hirschmann, produced camera-ready copy. The translation volumes, produced in paperback, are intended to be read in conjunction with the documentary edition, as they contain none of the editorial commentary of this edition.