4 6 8 D O C U M E N T 4 7 5 F E B R U A R Y 1 9 2 7 475. To Teodor Schlomka [Berlin,] 6 February 1927 To Mr. Teodor Schlomka, Dear Colleague, I unfortunately cannot share your hopes, at least not on the basis of the argu- ments you gave.[1] 1) As soon as you retain the electromagnetic equations in a vacuum, the follow- ing transformation equations hold: From this it follows, however, that (for small ) the supplement to the electro- magnetic field arising out of this motion always stays correspondingly small. Therefore, an effect can only be expected of this experiment if the vacuum equa- tions are modified. 2) But if one then makes abstraction of all theory, and assumes that in general the rotation of mass directly generates a magnetic field, then one would have to ex- pect that the translation of the masses generally would generate a field acting on the magnet. Then the modification would have to produce an effect by a supple- mentary motion that is of the relative order of magnitude of the proportion . Navigation between South America and Europe would then already have called attention to it.[2] 3) I think that the Americans would have had to discover such a coarse effect with their wooden motorboat for magnetic measurements.[3] Thus, if you cannot advance any better arguments for the anticipated effect, I don’t have any justification to apply for the 500 marks. Hopefully you can con- vince me that your experiment is not unpromising. Kind regards, your A. Einstein ex′ ex = ey′ ey v c -- hz – 1 v2 c2 ---- -– ------------------ = – – – – – – – – v c -- additional velocity velocity due to rotation -------------------------------------------------------