2 4 2 D O C U M E N T 2 4 8 A U G U S T 1 9 2 8 I hope I have expressed myself sufficiently clearly the contents of my previous letter were taken for granted.[9] The centrally symmetric solution is thus also possible therefore, we might hope that the quantum theory would perhaps most readily be obtained through your method of (continued) overdetermination.[10] One could, for example, also take the second of your invariants into account.[11] But, without your direct wishes, I don’t want to add any more here, and remain in the meantime, With best wishes from house to house, yours very truly, H. Müntz 248. To Roland Weitzenböck currently at Scharbeutz bei Lübeck, 3 August 1928 Dear Colleague, I thank you sincerely for your communication, which naturally was of extremely great interest to me.[1] I wrote the two notes while in bed, since I was ill from a se- rious heart ailment, and still am.[2] I requested that my colleague Planck ask the mathematicians in the Academy whether these formulations were already known, before submitting my notes for publication.[3] However, he replied that a publica- tion would be justified from the physics standpoint alone, and I went along with him. I should be quite content if you would write a note for our Academy to clarify this point. As a matter of fact, I have to tell you that this method now appears to me to be much less promising than I had initially thought. The indeed fulfill the Maxwell equations, but there is not an h field[4] for every solution of the latter. It is not even possible to find a centrally symmetric electric field. If you are in agree- ment, I would add a note of my own to yours, in which I point this out as briefly as possible. As firm as my belief is that the space-time field is unified, it appears that the secret of this relationship is quite deeply hidden. Kind regards from your A. Einstein     =