2 8 2 D O C U M E N T S 3 5 2 , 3 5 3 S E P T E M B E R 1 9 2 2 352. To Alfred L. Berthoud[1] Berlin, 14 September 1922 Esteemed Colleague, Please excuse me for answering your letter of 28 Dec. of last year only today [2] far too much correspondence is to blame. It just came to hand as I was looking through the accumulated mail and I hurry to pick up the arrears. The correct mass is the one calculated out of the energy. The electromagnetic mass has to be increased by the additional mass that the moving body possesses because it is subjected to mechanical tensile forces by the action of the electric charges. This follows from the energy’s tensor character in relativity theory. It should generally be noted that an energetically negligible frame as carrier of elec- tric masses cannot exist in the interpretation of relativity theory. Bibliographic ref- erence, e.g., von Laue, Relativitäts-Theorie, 1st volume.[3] Very respectfully. 353. To Thorvald Madsen[1] Berlin, 14 September 1922 Esteemed Professor, Prof. Einstein asked me to thank you for your kind message and to tell you that he will be glad to keep noon of the 22nd [inst.] open for an interview with you.[2] Mr. Comert[3] already had the kindness to inform Prof. Einstein about the in- tended election of a German medical doctor to the “Committee on Intellectual Cooperation.” Prof. Einstein would now like to know whether all of you have already identified a suitable person he himself was thinking of Priv. Councillor Prof. Kraus[4] but has not taken any steps yet. If you think it useful that Prof. Ein- stein do something to prepare the matter before your arrival in Berlin, please have a pertinent message sent out to him. In utmost respect, The secretary.