4 6 D O C U M E N T 2 3 J U L Y 1 9 2 5 already the intent of the French government in its offer. If this establishment was inspired (as some seem to think, from what you write) by an idea of national inter- est, the cool reception of the project in France would be incomprehensible. You know that the senate kept the project on hold for six months —it only just voted on it.[6] The truth is that this creation of an international institute was seen for what it really is, a gift made by France to the League of Nations (and this, they say, at a moment when France scarcely has the means to make gifts). Please accept, my dear colleague, my most sincere regards, H. Bergson 23. From Max Born Göttingen, 15 July 1925 Dear Einstein, We were very pleased with your kind note. My wife left with the children[1] for Silvaplana in the Engadin the day before yesterday and will probably write you from there. I want, in the meantime, to tell you a bit about us. As for physics, to start with, your kind words about my activity spring from the goodness of your soul. However, I am aware that what I am doing is quite mundane stuff compared to your or Bohr’s ideas.[2] My idea box is very rickety, there’s not much in it, and what is in it rattles back and forth, has no fixed shape, and becomes increasingly complicated. Your brain, heaven knows, looks much neater. Its prod- ucts are clear, simple, and to the point. We catch on, if need be, a few years later. That’s the way it was with your gas degeneracy[3] and Bose’s statistics.[4] Luckily, Ehrenfest showed up here and shed some light on it for us.[5] After that, I read Louis de Broglie’s article[6] and gradually came to understand what you are up to. Now I believe that the “wave theory of matter” may become a very important thing. The reflections of our Mr. Elsasser are not yet properly organized to start with, it has turned out that he really miscalculated—but I still think that the substance of his remarks, particularly concerning the reflection of electrons, can be salvaged.[7] I am also speculating a bit about De Broglie’s waves. It seems to me that there is a connection (of a completely formal nature) between them and that mystical expla- nation of reflection, diffraction, and interference using “spatial” quantization as Compton and Douane proposed, and as Epstein and Ehrenfest have investigated in detail.[8] Primarily, I am, however, interested in the quite mysterious differential calcula- tion that seems to be behind the quantum theory of atomic structure.[9] Together