1 0 4 D O C U M E N T 8 8 M A R C H 1 9 2 2 in—I shudder to say—French [3] I announced a course here for the summer term starting around 1 April [4] and I have to visit you in May, and do it properly, too, because I was unable to resist the sirens of East Asia.[5] So this is how I’ll do it: I’ll be teaching here just in June and July, but therefore twice a week instead of once. This won’t be that bad because after my return, hence still during the winter semes- ter, I can still come to Leyden again. This is possible, since I am putting my duties here on hold for half a year. So, with God’s help, everything will turn out all right and you don’t need to get agitated. Thank Onnes in my name for having performed the experiment. It would have been nicer still if he had done it with a closed circuit, but this way probably suffices as well.[6] The result of the experiments with sound in N2O4 ⇔ 2NO2 was that the reaction follows the sound vibrations.[7] So the reaction must be very rapid. I then suggested comparing the amplitude of the sympathetic vibrations with the one for normal gases, since a reaction speed not infinitely large acts as an energy dissipator, hence it diminishes the amplitude. It is actually good that I have so many distractions because otherwise the quan- tum problem would have driven me to the insane asylum long ago. The fact that light, emitted in diametrically differing directions, can interfere has supposedly been irrefutably demonstrated.[8] How is that supposed to be reconciled with the energetic directedness of elementary processes? How pitifully the theoretical phys- icist stands before nature and—his students! 88. From Maurice Croiset [Paris,] 15 March 1922 Sir, The assembly of professors at the Collège de France has, as Mr. Langevin has already let you know,[1] decided at its last meeting to ask you if it would be possible for you to come to the Collège to deliver some lectures. The favorable response[2] Mr. Langevin has informed me about authorizes me to confer with you about orga- nizing these lectures and to ask you please to let me know your intentions in this regard. As the Collège is closed every year during the Easter holidays (i. e., this year from April 9 to the 23rd of that same month), the lectures you would be so kind as to deliver would have to take place either before April 9 or after the 23rd. It would