In the early 1970s I wrote a profile of Albert Einstein for the New Yorker. I had known his secretary Helen Dukas since my days at the Institute for Advanced Study. She had come with him when he emigrated from Germany and lived in the Einsteins’ house in Princeton, which after his death she shared with his stepdaughter Margot. I asked if I could visit the house. She agreed. In Einstein’s study there was an etching of James Clerk Maxwell and one of Newton which had come out of its frame. This seemed symbolically correct. Helen offered to make lunch and while she was preparing the sandwiches she gave me a book to look at. It included a letter Einstein sent from Brussels to his wife Elsa in 1930.