D O C U M E N T S 1 6 , 1 7 J U LY 1 9 2 7 3 9 16. To Frederick Alexander Lindemann [Berlin, after 3 July 1927] Dear Lindemann, I thank you warmly for your friendly letter with its invitation. How gladly would I accept, particularly as I value highly the milieu of English intellectuals, as being the finest circle of men that I have ever come to know. Unfortunately, how- ever, I cannot come. My work here is very much tied up with other people so that I cannot be away for such a long time. My health is poor, so that a long stay in for- eign and unfamiliar surroundings would be too great a burden for me, particularly bearing in mind the language difficulty. Finally, I must also tell you that the material that I could bring would disappoint my listeners as it has insuffi- cient up-to-date interest. You can today find many more experienced people than me. I must, however, offer my heartfelt thanks to you and to all those who have joined in this invitation. I am very conscious of the value of the trust and friendship that has been shown toward me. The reasons against my coming are, however, so strong that you will easily understand that I cannot accept your invitation, much as I regret it. Kind regards from your A. Einstein 17. From Max Barthel Strasbourg, 4 July 1927 Dear Professor Albert Einstein, Please allow me to briefly occupy your time. I am writing concerning the matter of the photochemical law of equivalence. In your articles in the Annalen der Physik, vols. 37 and 38, 1912, you have studied the extraordinary thermodynamic equilibrium of a dilute gas on the basis of certain assumptions you thus arrive at an expression for  that has the same form as that obtained by Wien. Wien’s formula appears as a result of your assump- tions.