D O C U M E N T S 2 0 4 , 2 0 5 M AY 1 9 2 8 1 9 9 that he understands things, and that he guides and prepares the board of trustees competently, and on the other hand is willing to devote the major part of his work- ing capacity to this administrative activity. I believe that Prof. Brodetsky fulfills these conditions and therefore I recommend to the board of trustees that he be selected. Sincerely, A. Einstein 204. From Paul Ehrenfest Leyden, 29 May 1928 Dear Einstein, Today I received a couple of particularly kind lines from Planck in thanks for my good wishes on the occasion of his seventieth birthday.[1] That gave me, via certain detours, an inducement to reread the polemic between Mach and Planck[2] in the Physikalische Zeitschrift for 1910, and your reply to Mach in 1916.[3] But that leads me to think of you with sincere fondness! I find what you wrote about Mach very very wonderful. That said, it remains a kind of paradox for me that you have never crushed but always encouraged and reinvigorated me! May God bless you, your 205. From Erwin Schrödinger Berlin-Grunewald, Cunostrasse 44, 30 May 1928 Dear Professor Einstein, Enclosed is a letter from Niels Bohr, who at its end expresses his wish that you and Dr. Planck also be informed of its contents. I also enclose a carbon copy of my letter to him, only so that you can see what initiated the discussion.[1] The remark on the uncertainty relation in an ideal gas, in more detail, is as follows:[2] If we quantize a molecule that is being reflected back and forth along the path l, then that gives d. h. . pdx p dx 2lp nh = = = p n nh 2l - =