ALS in German, signed “M. Planck,” three pages on two adjoining sheets, 5.5 x 8.5, January 25, 1920. Handwritten letter to Dr. Ludwik Silberstein, following up on the missing platinum standard and once again defending Einstein's theory. In full (translated): "It is high time that I report to you about the inquiries conducted here on my initiative in search of the location of the Pt standard in Brussels.
My colleague Prof. Haber, at my request, contacted Col. (Ret.) [Oberst a. D.] Koeth, who as head of the War Raw Materials Division [Kriegsrohstoffabteilung] during the war was the top-ranking official responsible for the confiscation and processing of raw materials for war purposes. He for his part made inquiries with the official responsible for the metal area, who also belongs to the Raw Materials Division, Mr. von der Porten.
I enclose here a copy of Mr. von der Porten’s letter in reply, as a product of the information collected, and I urge you most devoutly to bring its contents to the attention of Major MacMahon. Unfortunately, more detailed inquiries can only be undertaken if more specific information about the missing piece of platinum is available. The matter naturally remains no less regrettable as a consequence.
Now, receive also many thanks for your friendly letter of the 7th of this month, which arrived here yesterday, with the proofs of your paper on the quantum theory of spectra. I have looked it over with great interest and find your presentation, as always, attractively readable, clear, and exhaustive on the essentials. I would not know how to make any suggestions for revision.
The Einstein theory of relativity has evidently stood up as well as could possibly be expected under the deflection measurements. I believe that this speaks very strongly in its favor. Where the displacement of the spectral lines is concerned, the question is still open in my opinion. I consider it very possible, however, that the decision will ultimately come down in favor of the Einstein theory here as well. In any event, there is for the moment no cause to reject it and look for another way out of the darkness." Silberstein notes the dates of receipt and reply at the top. In fine condition, with short edge splits to folds.
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