D O C U M E N T 2 6 0 A U G U S T 1 9 2 8 2 5 5 260. To Chaim Herman Müntz Scharbeutz, 27 August 1928 Dear Mr. Müntz, Many thanks for your card. I will stay here for the rest of September. So that our cooperation is not interrupted, I am writing you a sufficiently detailed letter about what I have found out regarding the law of motion. The most important thing is to find the equations of motion in first order for charged and uncharged mass points from the new field laws,[1] so that we can see whether they agree with the known laws for if that is not the case, we would have a clear-cut refutation of the new the- ory. As you indeed know, in the new theory (all the other h = 0) is a solution in first approximation (mass points), and so is the result that you found, (all the other h are 0),[2] as well as a linear combination of these two. Whether there are corresponding exact solutions, and whether they have a singu- larity at , is a question of its own, which we can leave aside for the moment. I will demonstrate the method for the theory of motions for you by using the old gravitation equations. I think that it can be applied in a similar manner to any other system of relativistic equations. 1) Remark on a special kind of solutions of the equation[3] . I write this equation in the form and seek solutions that will be expressed as series expansions in the constant . I start from the approximation , where the are slowly varying functions of time. The are assumed to be small to first order in , also small in second order. I take h4 4 r = h4 a j---- x a r - = r 0 = 0 = 2 x 1 2 2 x 2 2 2 x 3 2 -------- 2 t2 - – + + 0 --------- 2 t2 – = = 0 r (r2 x – 2) = = 0 t -------- - + r 2 2 x – r ------------------------ -[4] · = 2 0 t2 -----------