Robert Jungk.
Brighter than a Thousand Suns: a personal history of the attomic scientists.
Pelican. 1958
First published as Heller als tausend Sonnen, in 1956; this translation by James Cleugh.
p31. One evening Paul Dirac, who was usually so silent, took Oppenheimer aside and gently reproached him. 'I hear', he said, 'that you write poetry as well as working at physics. How on earth can you do two such things at once? In science one tries to tell people, in such a way as to be understood by everyone, something that no one ever knew before. But in the case of poetry it's the exact opposite!'