D O C U M E N T 2 4 J A N U A R Y 1 9 2 2 4 3 * Crossed out text: “In my opinion I had deemed the following wording for the main claim correct: “. . . that pliability and ductility of the wires in a cold state is achieved in that in their manufacture they are subjected to a larger number of reworkings than would be necessary for the mere shaping of the wires.” With this I wanted to express that under the circumstances the production of the wires only involved shaping and not an alteration of the material’s properties. Thus the procedure is only protect- able insofar as ductility not be attainable without this mechanical reworking. Therefore, if, for instance, it were possible to cut out a thin strip from this tungsten mass and already be able to ascertain ductility in it, then any mechanical reworking of such a tungsten mass would be free.” 24. From Paul Ehrenfest Leyden, 17 January 1922 Dear Einstein, Owing to a somewhat overly hurried trip homeward, your postcard reached me only here.[1] Damn it! If your light experiment really does come out anti- classically[2] —I mean, after not just theoret. but experimental critique—then – – – Well, you know, then you give me the spooks.– Don’t laugh at me. I mean it entirely seriously. I’ll write to Bohr about it now. I’m very eager to know how he’ll react to it.– Assuming I am capable of reproducing his opinion about these things correctly, I would like to formulate it like this: He is much more ready to give up the energy (and momentum) law (in its classical form) for atomic elementary processes (and therefore just to uphold statist.) than “to shove the blame onto the ether.” (He is guided by the totality of his studies on atoms–) In any event: If your result is true-blue, then—it seems to me—you found some- thing quite enormous. = : = This also: You told me at the time that a Spanish professor—(University of Madrid?) is interested in the results that you and I obtained here in Leyden with the concentration of Au ions.[3] – Thanks to the arrival of a new preparation from Methuen and a preparation that has just been produced here in Leyden proper, the concentration has been brought up to 6.7 × 10–3.[4] This is already quite a usable figure. So if you pass the address of this noble Spaniard on to me, I can send him the measurement results directly. Very cordial regards to all of you—but especially to the dear Ilmargotse.[5] P. Ehrenfest