2 5 8 D O C U M E N T 2 4 6 A P R I L 1 9 2 6 constants, has two singularities, namely: the one of field f and the one of field F. These singularities are characterized by numbers (i.e., residues) which depend on λ , resp. μ, and are thus arbitrary therefore, no relation can exist between them. However, in the nonlinear case, this consideration does not apply, because λ f + μF does not need to be a field if f and F are fields (i.e., λ f + μ F does not need to satisfy the field equations), and it can very well happen that relations exist between the residues ¢of such a field² in this case. But I have taxed your time too much al- ready and must finish. Respectfully yours, with kind regards, G. Y. Rainich 246. From Hendrik A. Lorentz Haarlem, 6 April 1926 Dear Colleague, When a week ago I was once again visiting Mr. Painlevé with Simpson, he posed the question about the selection of the persons who should be invited to the much-debated small preparatory conference. I said that, in my opinion, Mr. Pain- levé and the German envoy in Paris, when they discuss this matter together, could also make this selection, by which I did not mean that they need make this choice themselves directly but only that they reach the decision after having them- selves been advised by others, insofar as they wish it. In particular, the German en- voy would know to what extent it is desirable that the Academy of Sciences be consulted. Mr. Painlevé was probably in agreement with what I had said, but stated that he would prefer to know in advance the names of a few German scholars who would be considered for invitation. I certainly do understand this as well he could then discuss this staffing issue better with the envoy. When he then asked me to name a few persons, I naturally mentioned Planck and Haber, whom he had already thought of as well, but I told him I would write to you about the others. You know these people much better than I. Would you now be so kind as to give me the names of a few other German schol- ars whom you deem suitable, shall we say, four to six, as soon as possible? That is, among them representatives of sciences other than physics and chemistry one mathematician could perhaps also be included. As relates to the number, Mr. Pain- levé was thinking of a composition for the conference roughly as follows: four Ger- mans, four Frenchmen, two Englishmen, two Italians, one Belgian, and one Dutchman. If I therefore suggest four to six others to him besides Planck and Haber, he will then have a better choice.