Two pages of handwritten calculations by Albert Einstein are providing one of the top lots in RR Auction's latest online sale.
The December 25, 1925 dated letter has received bids of $25,941, with the auction due to close on August 14.
The document is addressed to a Jewish Student Union in Germany, with the physicist giving the students a glimpse into his current attempts to generalise his geometric theory of gravitation - a project that followed his research on general relativity.
It reads: "To the Jewish Student Union in Germany, I wish your conference the best of success. I would gladly be present myself, but unfortunately urgent work prevents me from the appearance. I always wish my utmost support, to demand your goals."
Einstein was a lecturer in Berlin at the time and served as the first president of the World Union of Jewish Students, which sought to address the issue of an unjust quota system that greatly limited the number of Jewish students admitted to European universities.
The calculations are accompanied by a letter from Edward Glass, professor of physics at the University of Windsor in Canada, which states that "the calculations on the Einstein letter are the kind that every physicist does informally and frequently."
"The two lines immediately below Einstein's initials are for the electromagnetic field."
Glass then goes on to identify computations for Einstein's gravity (general relativity) and components for the Ricci tensor for an electromagnetic field source.
Paul Fraser Collectibles has a superb signed document from Thomas Edison, which is the annual report of the Edison Spanish Colonial Light Company.