x l v i I N T R O D U C T I O N T O V O L U M E 1 3 by Grommer conveyed to Einstein in a letter of 25 October 1921 (Vol. 12, Doc. 283). The immediate motivation for this publication was to promote a new scientific journal published by the Hebrew University in Jerusalem, which had not yet officially opened. Most likely, the paper was also meant to assist Grommer in establishing a career at the planned university. The paper is related to Theodor Ka- luza’s idea, already conveyed to Einstein in 1919, of a five-dimensional space that would incorporate the electromagnetic field via the fifth dimension (see Vol. 9, pp. l–li, and Vol. 12, p. xlviii). It purports to show that Kaluza’s theory does not admit static, spherically symmetric solutions that obey certain boundary conditions at in- finity. The significance of the result was that this class of solutions could have been interpreted as particle-like field configurations. Field configurations representing particles would have to be localized, i.e., their nonvanishing field values would have to be restricted to a finite region in the space- like dimensions. They also should be static, at least for single-particle solutions. The existence of such solutions was part of Einstein’s vision for a truly unified field theory. The idea goes back to a suggestion by Gustav Mie made in the context of Lorentz-covariant electrodynamics and developed by David Hilbert and Hermann Weyl. The impossibility theorem proven by Einstein and Grommer therefore showed the nonviability of Kaluza’s Ansatz, at least as far as a strict pursuit of Ein- stein’s expectations for a unified field theory was concerned. The second relativity paper in the present volume, “Zur allgemeinen Relativi- tätstheorie” (Einstein 1923e, Doc. 425), was completed a year later, on 22 January 1923. It was conceived during Einstein’s long sea voyage back home from the Far East (see also Docs. 417, 419, and 418) and is discussed in section IX below. V Einstein’s trip to Paris in late March and early April 1922 represented an important breakthrough in the postwar rapprochement between the German and French sci- entific communities. Yet it took quite some persuasion to get Einstein to agree to the visit. Already in late 1921, the French League for Human Rights had asked him to participate in its joint meeting with a delegation from the Bund “Neues Vater- land,” and Paul Painlevé had invited him to the International Congress of Philoso- phy. But Einstein had declined both.[11] In February 1922, Paul Langevin conveyed an official invitation to Einstein by the Collège de France to deliver the Michonis Lectures, intended for a general au- dience. Not only was the Collège, as well as the students and the public, “desirous