D O C . 4 5 5 T R A V E L D I A R Y 6 9 9 [1]Elsa Einstein. Moritz Katzenstein, who had five sisters: Henriette, Rosa, Sara, Emma, and Paula. Alexander Bärwald (1877–1930) was a German-Jewish architect who designed the Technion building in Haifa. His wife was Charlotte Bärwald-Eisenberg (?–1937). [2]In Hamburg. [3]Marie Robinow-Rosenfeld (1883–1965) was the wife of Hamburg Jewish lawyer Richard Robinow. [4]Carl Melchior (1871–1933), who was a Hamburg Jewish banker, a partner at M. M. Warburg & Co., and chairman of the Supervisory Board of Beiersdorf AG. [5]The SS Cap Polonio was owned by the Hamburg South American Line. [6]Robinow. [7]Margot Einstein had apparently been planning to accompany Einstein on his trip, but had pre- sumably fallen ill shortly before the planned departure (see Doc. 457). [8]Carl Jesinghaus (1886–1948) was Professor of Philosophy and Psychology at the University of Buenos Aires. [9]Ideas about the foundations of Riemannian geometry, the mathematical framework for the gen- eral theory of relativity, had previously been the starting point for approaches to establish a unified field theory of the electromagnetic and gravitational fields. One such approach was following up upon the work of Hermann Weyl and Arthur S. Eddington, and based Riemannian geometry on the concept of the affine connection. On his return trip from Japan in early 1923, such an idea had led to Einstein’s exploration of this approach, resulting in the publication of Einstein 1923e (Vol. 13, Doc. 425), 1923h, 1923n (Docs. 13, 52). By mid-1923, Einstein had abandoned this approach (see the Introduction, pp. xxxvii–xl). Later in 1925, however, he would publish on a new approach to a unification of the fields based on the assumption of an asymmetric metric see Einstein 1925t, presented to the Prussian Acad- emy on 9 July 1925 Chaucer 1924. [10]Elsa Jerusalem-Kotányi (1877–1944?) was an Austrian-born writer who lived in Buenos Aires. [11]Possibly Johannes Sievers (1880–1969), art historian and Legationsrat at the Auswärtiges Amt. [12]Probably the Castelo de São Jorge. [13]The Mosteiro dos Jerónimos. [14]Meyerson 1925. [15]Perhaps Einstein looked at the variation of the integral over paths parametrized by s for given fixed (“feststehenden Lichtkegeln”) and given fixed and given coordinate system. If the external path is interpreted as an electron orbit, i.e., an orbit for any charged particle of charge over mass ratio , motion on that orbit would create a back reaction to the electromagnetic field. Appar- ently, he would have concluded then that the electromagnetic field has no degrees of freedom in this construction. [16]Koigen 1925. [17]Einstein turned forty-six on 14 March. [18]Presumably Fogo, one of the islands of Cape Verde. [19]The equivalent of 28°C and 84° F. [20]Einstein had once already considered these trace-free field equations (which differ from the field equations of general relativity by having a factor of ¼ instead of ½ in front of the second term), in Einstein 1919a (Vol. 7, Doc. 17) see its equation (1a). For a historical discussion of these field equations in the context of Einstein’s attempts at a field-theoretic description of matter, see Sauer 2012. For earlier doubts about the viability of field theory, see Einstein 1924d (Doc. 170), §1. [21]Wolfgang Amadeus Mozart, “Eine kleine Nachtmusik,” KV 525, and Ludwig van Beethoven, “Romanze” No. 2, F major, op. 50. [22]Abbreviation for “Mitglied der reichen Faulenzerklasse,” the German translation of MIRC— “member of the idle rich class” in Shaw 1919 (see also Doc. 269, note 5). [23]In Bohr’s theory of light emission in terms of electronic transitions between quantized orbits of different energy, the problem arose how to explain that the emitted light quantum appears to travel as a directed particle, whereas the emitted light could also show interference phenomena. In 1922, the problem had motivated an unsuccessful experiment to decide between a particle and a wave picture gμν ϕμ ε m --- -