6 6 D O C U M E N T 5 4 S E P T E M B E R 1 9 2 7 should necessarily be equal to the particle radius that makes itself apparent e.g. in deflection experiments, is an assertion that is unfortunately not supported by any evidence. With the same degree of correctness or incorrectness, one could also adopt the following interpretation: For the overall mass of the world and for its radius, the relation holds (leaving off an unimportant numerical factor, which I will permit myself to do in the following).[1] If we add a particle of mass , then the radius of the world increases by . The increase of the volume of the world is then . Since corresponds to the “particle volume,” we then find for the “particle radius,” while in your case, would result. It might also be possible that something like your relation would be found: a : = : (since that is what one essentially obtains by considering only the orders of magni- tude), but you have not stated a reasonable justification for something of this kind. The quantity that you calculate simply makes no apparent experimental-physical sense in any case, you have not demonstrated or made it plausible that it has such a sense. Best regards, your A. Einstein a m 2 3 --ma + = M a = M a = = V a2a a3 = a2 = = V a2 3 a 2 R