All the letters were written by Einstein, the father of the theory of relativity, to Margarita Konenkova between 1945 and 1946. They have been passed on to Sotheby's, the auction house, by an unnamed relative of Konenkova. With other mementoes of the affair, they will be sold on 26 June.
The missives reveal a man smitten with a woman who at the time was married to the Russian sculptor Sergei Konenkov. She had apparently also had an affair with Sergei Rachmaninov. Whether the relationship began before or after the death in 1936 of Einstein's second wife, Elsa, is not clear.
Much more likely to stir fascination in the sale, however, are suggestions that Konenkova was a Russian spy and that introducing Einstein to Soviet diplomats in New York was part of her mission.
Konenkova's secret side was, according to the New York Times, uncovered first by Paul Needham, a consultant to Sotheby's. Mr Needham stumbled on references to her in a 1995 book written by the Soviet spymaster Pavel Sudoplatov and his son Anatoly, called Special Tasks.
Konenkova, the book suggests, had been directed by Moscow to pay special attention to the Manhattan project. Headed by scientists such as Robert Oppenheimer at a secret installation in the New Mexico desert called Los Alamos, the Manhattan project was the cradle of America's atomic bomb.
According to Special Tasks, Konenkova was supposed to "influence Oppenheimer and other prominent American scientists who she met at Princeton". Princeton University was home at the time to Einstein. It is known that she succeeded in introducing Einstein to the Soviet consul in New York.
There is nothing in Einstein's letters, all written in German, to suggest that the author had any notion of Konenkova's role as a spy. And since Einstein had no direct role in the Manhattan project, it seems improbable that he could have helped, consciously or otherwise, in Moscow's effort to build its own bomb.
Instead, the letters reveal a soppy side to Einstein that has barely been seen before. In one, dated 27 November 1945, he writes: "Just recently I washed my head by myself, but not with the greatest success; I am not as careful as you are. But everything here reminds me of you: Almar's shawl, the dictionaries, the wonderful pipe that we thought was gone, and really all the many little things in my hermit's cell".
"Almar", it is supposed, is an elision of the first names Albert and Margarita.Reuse content