Thomas J. Ritzinger to Richard P. Feynman, March 2, 1966 / Richard P. Feynman to Thomas J. Ritzinger, March 15, 1966 / Richard P. Feynman to Mary E. Hawkins, March 21, 1966 by Thomas J. Ritzinger & Michelle Feynman narrated by Johanna Parker / Richard P. Feynman narrated by Richard Poe