D O C U M E N T 3 0 0 J U N E 1 9 2 6 3 1 7 Zeitschrift für Physik. It takes too long for things to appear in the Annalen, espe- cially since we are talking about a matter of current interest. If you need to know further theoretical details for the second experiment, I am of course available. Best regards, your A. Einstein Translators’ note: Translated by Doris Lonk and Tilman Sauer. 300. To George Y. Rainich [Berlin,] 6 June 1926 Dear Mr. Rainich, I completely agree with you on the main point. If a theory gives a solution which represents two electrons at rest, then it is inadequate.[1] This was indeed the reason why I thought that I had to reject a theory which regards electrons as singularities. For I had thought to have seen that any such theory would have solutions with elec- trons at rest. But it now seems that I was wrong about this.[2] Either way, this is the core question: A theory is sensible only if it allows to derive the equations of motion of particles without any extra assumptions.[3] Whether or not the electrons are treated as singularities does not really matter in principle.[4] I do entirely approve of your program with those 3 points. If one did succeed in deducing the necessity for the equality of electrons from differential equations, that would be an enormous advance. We likewise agree that ¢electric² magnetic masses are not supposed to exist. Your comment in this regard was not quite clear to me, though.[5] It is very commendable that you are pursuing the fundamental problems with such energy. I appreciate this much more than the aspiration for momentary successes. With kind regards, your A. Einstein