D O C U M E N T 1 2 5 J A N U A R Y 1 9 2 8 1 3 5 However, I still believe that an (affine) unified theory of gravitation and electric- ity can be constructed, based upon the asymmetry of the and avoiding the ar- tificial combination . I take the liberty of stating the preconditions very briefly (so as not to take up too much of your time), from which one can proceed to calculate the explicitly to an arbitrary precision, and can obtain to first approximation the gravitation equa- tions and the Maxwell equations. 1) The components of the parallel translation are in the general case not symmet- ric. 2) The length of a rod is not changed by a translation. 3) The covariant derivatives of the electromagnetic field strength are given by: = current vector. 4) In matter-free space, the equation holds. I would be very grateful to you, dear Professor, if you would be so kind as to let me know your opinion of the preconditions as given above. In thanking you for your kindness, I sign most respectfully, L. Infeld 125. To Leopold Infeld [Berlin, after 6 January 1928] Critical answer Condition that covariant. Formal derivation not very natural Separation of the symmetrical & antisymmetrical parts of Law of motion? ” l i g i i i + = l i i l i l g sl s i s i – g sl Il i I ike I i = = = R i 0 = g l i i = – .