Jørgen Veisdal in Cantor’s Paradise:
Letter from Norbert to Bertha Wiener (July, 1925):
There was a nice Swiss student from the Dresdner Technische Hochschule on the train from Leipzig. He talked very good English, and we had an animated conversation in both languages. We breakfasted together in the dining car leaving Frankfurt. At a nearby table I saw a strangely familiar face, and remarked to my comrade “I’ll eat my hat if that isn’t Einstein!”
After breakfast I decided (in view of his friendship with Lichtenstein, of my profession, and of the fact that I had been introduced to him in the States) to look him up.
I found him in a third-class compartment, and it was Einstein after all. When I said I was a mathematician, he began quizzing me about my line. He was quite impressed by my new light stuff. He then began telling me of his reduction of gravitation and the Maxwell equations to a single minimization problem. This is brand new stuff — its not out yet, and he only wrote it three weeks ago.