Below is a sheet from a 54-page Einstein manuscript that recently sold for $13 million at a Christie's auction in Paris. The handwritten note at the bottom right, dated Sept. 1939 — one month after the physicist, in a letter, advised President Roosevelt to begin developing an atomic bomb — is signed by one David A. Rothman (also pictured below) of Nassau Point, Long Island, where Einstein was summering. Rothman was a local store owner who had an interest in physics, although he never finished high school. He also played the violin (poorly), which helped to strike up a friendship with the more accomplished musical physicist.
If you can't make it out, the handwritten note reads: The above calculations are in Prof. Einstein's own hand used to explain to me without the use of mathematics the reason for the contraction of a rod in the direction of its motion and why a clock changes its rhythm. (I trust Rothman understood Einstein's calculations better than I.)