33 Moral Problems of a Scientist. The Atomic Bomb 1942–

One day during the Second World War I was called down to Washington to see Vannevar Bush. He told me that Harold Urey, of Columbia, wanted to see me in connection with a diffusion problem that had to do with the separation of uranium isotopes. We were already aware that uranium isotopes might play an important part in the transmutation of elements and even in the possible construction of an atomic bomb, for the earlier stages of this work had come before the war and had not been made in the United States.