D O C U M E N T S 2 2 8 , 2 2 9 J U N E 1 9 2 8 2 2 5 228. To Maria Julius [Berlin, 21 June 1928][1] Dear Maria Julius, Hopefully everything went well. Your calming words have made a deep impres- sion on me. As long as we live, our heartfelt relationship will not end the visit to the three of you will always represent the happiest episode of the trip to Holland.[2] Please have your loved ones tell me right away how you are doing. During our last visit you were so satisfied with the Bircher treatment.[3] How did this turn for the worse come about? I have ups and downs, but on the whole I am doing better. However, I probably won’t be able to come back to Holland in the near future. My heart demands rest. I wish you most warmly a prompt recovery. When you are allowed to again, take regular short walks in the open air, in pleasant company, and also cold showers on the arms and legs to improve circulation. In the hope of soon hearing good news, warm regards, your A. Einstein 229. From Curt Schwarz[1] [Berlin,] Monday, 25 June 1928 Dear Professor, It is with a heavy heart that I must inform you that because of an urgent lecture and lessons that I must give, it will be impossible for me to visit you tomorrow. I ask you to consider this as a necessary and sufficient punishment for my behavior and it only remains for me, putting many other things aside, to point out a very neat connection between the and the , of which you yourself may have already become aware.[2] Indeed, let or, brevitatis gratia, 1.) 1a.)g then, as one can see immediately, , providing that one sets h  .    dH  h  .  dx  = dH Hdx = dH'  dx'H'  = dH'dH  ds 2  dx'  H'H dx   = G g     H'H =  .  h .    h = 1 2         +   g  1  =