D O C U M E N T S 1 8 4 , 1 8 5 M AY 1 9 2 8 1 8 3 184. To the Tafelrunde vom Dornbusch[1] Berlin W., 6 May 1928 To the Dornbusch Roundtable: You have moved my hardened heart (which is also currently enlarged) by your persistence. Would any of you have wagered that I would actually reply?[2] Be that as it may, you can hardly imagine yourself in the position of a person like me who is persecuted by his contemporaries’ love and hunger for autographs. The mailman recently noticed that one of the people on his route still received more letters than I do, namely—the bailiff! Thus there are thorns in my case as well, not to mention the ones that make the path of science so painful. In any event, may your Dornbusch prosper and never lack the noble humidity that constitutes its vital element. In this spirit, kind regards from your A. Einstein 185. To Ernst Eckhardt Berlin, 8 May 1928 Dear Sir, Your separation of energies into Types I and II [1] appears to me to be very sim- ilar to the classification into potential and kinetic energies, as is usual in classical mechanics. However, physicists have stopped attributing any significance in prin- ciple to that classification, since Maxwell’s theory of the electromagnetic field has shown us a form of energy in the electromagnetic field that does not allow for such a classification in any natural manner. The situation in the theory of gravitation is analogous. In the current view of physics, your position is thus not very propitious, although a definitive statement about such a general problem is hardly possible. With best regards, A. Einstein