"Horizon (The Pleasure of Finding Things Out)". Documentary (November 23, 1981), later published in "No Ordinary Genius: The Illustrated Richard Feynman" edited by Christopher Sykes (p. 239), 1994.
"The Feynman Lectures on Physics". Physics textbook by Richard P. Feynman, Robert B. Leighton, and Matthew Sands, volume I; lecture 1, "Atoms in Motion"; section 1-2, "Matter is made of atoms"; p. 1-2, 1964.