D O C U M E N T 2 6 9 A P R I L 1 9 2 6 2 8 3 But I must return to one point in your letter on this topic. You say in response to my request to deliver a report to us that you would only have familiar things to say and that we might give the presentation to Schrödinger (because of his latest publications). I must comment here that we were thinking of two presentations, namely: “Adaptation of the foundations of dynamics to quantum theory,” and “New deductions of Planck’s law and application of statistics to quanta.” We are hoping to get the former from Heisenberg, or perhaps from Schrödinger and in any case his new “wave mechanics” belongs here. The second report goes in a different direction and I am convinced that if you would be so kind as to take it on, that something very interesting will come out of it. It does not need to be totally brand new, and, anyway, you do not need to stay entirely within the limitations indicated in the title. I thus remain hopeful of your cooperation. Now one more question. As you know, we must restrict ourselves very much as regards the number of participants, and so three Germans will be among them (not counting yourself), namely, Planck and two out of the hree: Heisenberg, Born, Pauli. When I said this to Ehrenfest, he immediately declared that it really would be very regrettable if we did not have Franck  he was thinking of him with Heisenberg. He came back to this later, however: Born had done so much for the development of quantum theory, and specifically for the new “mechanics,” that he could scarcely be passed over. Consequently, Ehrenfest is satisfied with Planck, Born, Heisenberg, and I, too, am of the opinion that this is the best choice. Would you be so kind, now, as to tell me what you think of this? If you would tell me soon, I would appreciate it very much, for I would like to send out the invitations at the beginning of next week, not because this matter is so very urgent, but in order to demonstrate our good will to the Germans as soon as possible. With kind regards, yours truly, H. A. Lorentz We shall naturally be able to invite Franck if one of the three others cannot come.