S.I. Vavilov's manuscript letter to Stalin

A letter from S I Vavilov, then President of the Academy of Sciences of the USSR, to Stalin has been discovered in the archives of the Science Department of the Central Committee of the Communist Party of the Soviet Union, which is concerned with the problem of secrecy in physics and suggests criteria by which classified and nonclassified studies may be distinguished. The letter is not only of interest to physicists and science historians, but also is a telling document of the totalitarian times, when it took no less than the states's top leaders to resolve issues as this.