Raymond R. Rogers to Richard P. Feynman, December 17, 1965 / Richard P. Feynman to Raymond R. Rogers, January 20, 1966 / Richard P. Feynman to Gilberto Bernardini and Luigi A. Radicati, February 9, 1966 by Raymond R. Rogers narrated by Johanna Parker / Richard P. Feynman narrated by Richard Poe