Feynman alludes to his thoughts on the justification for getting involved in the Manhattan project in The Pleasure of Finding Things Out. He felt the possibility of Nazi Germany developing the bomb before the Allies was a compelling reason to help with its development for the U.S. He goes on to say that it was an error on his part not to reconsider the situation once Germany was defeated. In the same publication, Feynman also talks about his worries in the atomic bomb age, feeling for some considerable time that there was a high risk that the bomb would be used again soon, so that it was pointless to build for the future. Later he describes this period as a "depression".

In which book did Feynman talk about the Manhattan project?