I N T R O D U C T I O N T O V O L U M E 1 5 x c i i i [1]The most notable examples of right-wing opposition to relativity took place in 1920 (see Vol. 10, Introduction, pp. xxxviii–xli, and Wazeck 2014). [2]See Vol. 14, Introduction, p. lxiii. [3]See the press release of the Bernisches Historisches Museum, “Einstein zog 500.000 Besucher an—ein Grund zum Feiern,” 24 March 2015. http://www.bhm.ch/fileadmin/user_upload/docu- ments/Medien/2015/Medienmitteilung_Einstein-Programm_D.pdf. [4]See Einstein to Marie Winteler, with a Postscript by Pauline Einstein, 21 April 1896 Marie Win- teler to Einstein, 4–25 November 1925 Marie Winteler to Einstein, 30 November 1896 (Vol. 1, Docs. 18, 29, and 30). [5]See Einstein to Pauline Winteler, May? 1897, and 7 June 1897 (Vol. 1, Docs. 34 and 35). [6]In her family history, Alice Rainich Nichols claims that her father was imprisoned because he was teaching relativity. She also describes how her father escaped the prison with the help of his wife and a prison guard who had been a former student of her father. For details, see Rainich 2013. [7]See also Einstein 1922r (Vol. 13, Doc. 387, note 2) for an argument as to why the two sets of field equations are indeed not equivalent. The validity of the 1919 trace-free field equations implies the validity of the 1917 field equations with cosmological constant, but not vice versa. However, this did not make a difference for the argument Einstein was making in that paper. [8]Einstein had already played with this possibility in a draft but then reverted to a purely affine approach in the published version Einstein 1923e (Vol. 13, Doc. 425). See Doc. 17, note 3, for details. [9]For a detailed analysis of how this change in Einstein’s thinking came about as a result of the correspondence with Rainich and how it fed into the writing of the paper by Einstein and Grommer, see Lehmkuhl 2017b. [10]See Lehmkuhl 2017a for further analysis of Einstein and Grommer’s reasoning, especially the question of whether they needed to commit to the existence of singularities. [11]Einstein would continue to work on this way of approaching the so-called problem of motion in general relativity his most influential paper on the topic is Einstein, Infeld, and Hoffmann 1938. Like Einstein’s paper with Grommer, Einstein, Infeld, and Hoffmann aim to derive geodesic motion from the vacuum field equations. The other major approach, which has been widely adopted despite Einstein and Grommer having considered it and opted against it, is to start from the full Einstein equa- tions and derive the geodesic motion of matter from the implied conservation condition of the energy- momentum tensor. For a review of the early work on this problem see Havas 1989 for reviews of recent developments see Asada et al. 2011 and Puetzfeld et al. 2015. [12]This charge has been echoed by Havas 1989. [13]Yang 1985 argued that Weyl, albeit possibly unwittingly, thus converted Einstein’s objection into a prediction, namely, that two electrons which take different paths through an electromagnetic field would end up acquiring different phases in their spin. This is similar to the well-known Aharonov-Bohm effect (see Aharonov and Bohm 1959). [14]See also Teodor Schlomka to Einstein, 2 December 1932 [21 524]. [15]See Schlomka to Einstein, 2 December 1932 [21 524] Schlomka to Einstein, 30 July 1927 [21 516] and Einstein to Schlomka, 3 September 1927 [21 518]. [16]See Lehmkuhl 2014 for an analysis of Einstein’s brand of rejecting geometrization as a major message of general relativity and Giovanelli 2016 for an analysis of the correspondence between Einstein and Reichenbach on the matter. [17]See Einstein to Eduard Einstein, 25 June 1923 (Vol. 14, Doc. 68). [18]Frieda was nine years older than Hans Albert, whereas Mileva was only four years older than Einstein. [19]The vehement opposition of Einstein’s parents, in particular of his mother, to his plans to marry Mileva, was based on her allegedly not descending from a “respectable family” and on her being older than Einstein (Vol. 1, Introduction, p. xxxvii, and Einstein to Mileva Mariü, 29? July 1900 [Vol. 1, Doc. 68]). [20]In 1917, Einstein had expressed remorse and self-reproach for having fathered children with Mileva, “a physically and morally inferior person.” Yet, at the same time, he admitted that his own