4 9 4 D O C U M E N T 3 0 0 J U N E 1 9 2 6 ALSX. [84 215]. Rainich had made this claim in Doc. 293. In Doc. 258, Einstein had argued against representing particles as singularities by referring to the existence of a solution, found by Hermann Weyl and elaborated on by Tullio Levi-Civita, that he interpreted as representing two particles at rest with respect to one another despite their mutual grav- itational reaction. He might have gone back to these papers since his previous letter to Rainich (Doc. 258). For in Einstein and Grommer 1927 (Doc. 443), the authors treat (a simplified version of) the solution as unphysical because of the existence of a singularity along the axis. The existence of this singularity was uncovered in Bach and Weyl 1922 see Doc. 258, note 4, for details, and Lehmkuhl 2017b for further analysis. In Doc. 293, Rainich had pointed out that in such a case the theory should not be abandoned but further conditions should be sought in order to find a more adequate solution. In Doc. 258, Einstein had claimed that the cardinal question was whether electricity is continu- ous or singular. In his reply (Doc. 293), Rainich had posed a different cardinal question, the answer to which was needed to solve three problems. The third of Rainich’s problems coincides with Ein- stein’s core question in the present letter. In his earlier attempts, Einstein had demanded to find nonsingular electron solutions (see Einstein 1925w [Doc. 92], note 2). See Doc. 293.