D O C U M E N T S 1 7 4 , 1 7 5 A P R I L 1 9 2 2 1 5 7 had been seriously considered by me before I postulated the special theory of relativity. I rejected this hypothesis at the time because it leads to great theoreti- cal difficulties (e.g., an explanation for the shadow cast by a screen moving relative to the light source). The most convincing refutation of this hypothesis, however, was given by the Dutch astronomer De Sitter, who drew attention to the fact that the light of one component of a binary star would have to be emitted at a temporally modified velocity, which, however, absolutely does not agree with the results of observations. In great respect. 174. To Elsa Einstein [Amsterdam,] Saturday [29 April 1922] Dear Elsa, After a good trip I arrived successfully in Amsterdam, where Ehrenfest was waiting for me at the station. In Bentheim they said—no second class. So your plan backfired, because it was more expensive than otherwise. We went to the academy. In the afternoon I gave a brief talk at the phys. society. In the evening I visited Zeeman. Now I am sitting in Amsterd. with Ehrenfest in the train and am writing you before the departure. I slept well last night. Amsterdam breathes contentment and abundance as always. I’m already looking forward to Leyden. Now it’s Ehrenfest’s turn. Warm greetings to all of you. Yours, Albert. Undersigned confirms proper receipt in undamaged condition (umbrella included) of the above-specified shipment. P. Ehrenfest, importer. 175. From Max Born Göttingen, 30 April 1922 Dear Einstein, Laue was here a short while ago we had a very good time with him. He told us that you are traveling to Holland. I hope this letter reaches you nevertheless.