2 0 4 D O C U M E N T 2 0 8 J U N E 1 9 2 8 208. From Leopold Infeld Warsaw, 2 June 1928 Dear Professor, I thank you sincerely, esteemed Professor, for the letter that I received from you in January of this year.[1] I take the liberty of briefly communicating the results that are obtained from my assumptions for the unified field theory. 1. From the assumptions for the theory, which are discussed in more detail in an article[2] that will soon appear in the Z[eitschrift] f[ür] P[hysik], it follows for as a function of the given state variables and [that we obtain] the equation: (1)  is a very small constant that is equal to the ratio of the field strength as expressed in the natural units and in practical units. denotes the Riemannian derivative. Here and in the following calculations, only those terms that contain  to first order are included. 2. As the differential equations of the theory, your differential eqns. have been taken. That is, (2) For , Eq. (1) is to be inserted into (2). 3. The symmetric part of (2) provides us with nothing new. Indeed, one obtains , and thus the fundamental equations of RT, which, as can be seen from your more recent articles, contain the law of motion. 4. The nonsymmetric part of (2) gives us (if I am not mistaken) the true form of Maxwell’s equations, which differs from the usual form. This is detailed in a note to the Parisian C[omptes] r[endus], which I have at the same time permitted myself to send to you.[3] Meanwhile, I take the liberty of thanking you most splendidly for the consider- ation that you have shown to me. I am greatly looking forward to, most likely, be- ing able to participate in the physics vacation course, which will permit me to deepen my understanding of your recent work through attending your lectures. Thanking you heartily once more, dear Professor, for your kindness, I am re- spectfully yours, L. Infeld  ik l g ik  ik  ik l l ik      1 2 --  i k l  k i l  ik s gsl + + + =  ik l  js s xk ---------- s jk xs ---------- – h js s hk + jk s hs = –T jk –h – sh jh g sk – 1 4 --g kj sh sh +  = l ik R ik –T ik =