Ilya Mikhailovich Frank (1908 – 1990) Signed & Completed Russian Air Mail Envelope, “I. M. Frank", blue ink, 6.25 X 4.25, postmarked with two c.1961 Russian stamps, and handwritten by Frank to a man in “Brooklyn, N. Y. USA”, and hand-signed in the return address at bottom: “I.M. Frank, Academy of Sciences of the USSR Moscow”, by the Soviet winner of the Nobel Prize for Physics in 1958 jointly with Pavel Alekseyevich Cherenkov and Igor Y. Tamm, also of the Soviet Union. He received the award for his 1954 work in explaining the phenomenon of Cherenkov radiation. The radiation is named after the Soviet scientist Pavel Cherenkov, also the 1958 Nobel Prize winner, who was the first to detect it experimentally under the supervision of Sergey Vavilov at the Lebedev Institute in 1934. Therefore, it is also known as Vavilov–Cherenkov radiation. Cherenkov saw a faint bluish light around a radioactive preparation in water during experiments. His doctorate thesis was on luminescence of uranium salt solutions that were excited by gamma rays instead of less energetic visible light, as done commonly. He discovered the anisotropy of the radiation and came to the conclusion that the bluish glow was not a fluorescent phenomenon. A theory of this effect was later developed in 1937 within the framework of Einstein's special relativity theory by Cherenkov's colleagues Igor Tamm and Ilya Frank, who also shared the 1958 Nobel Prize. Frank also received the Stalin prize in 1946 and 1953 and the USSR state prize in 1971. This attractive hand-signed envelope is in fine condition.