Richard P. Feynman to Thomas K. Moylan, March 25, 1963 / Ernest D. Riggsby to Richard P. Feynman, April 17, 1963 / Richard P. Feynman to Ernest D. Riggsby, April 30, 1963 / Richard P. Feynman to D. Blokhintsev, June 25, 1964 by Richard P. Feynman narrated by Richard Poe / Michelle Feynman & Ernest D. Riggsby narrated by Johanna Parker