Albert Einstein (2015). “Bite-Size Einstein: Quotations on Just About Everything from the Greatest Mind of the Twentieth Century”, p.32, St. Martin's Press
George Bernard Shaw (2015). “George Bernard Shaw: The Collected Plays (Illustrated): 60 plays including Caesar and Cleopatra, Pygmalion, Saint Joan, The Apple Cart, Cymbeline, Androcles And The Lion, The Man Of Destiny, The Inca Of Perusalem and Macbeth Skit”, p.2919, e-artnow
Back to Methuselah pt. 1, act 1 (1921). This was a favorite quotation of Robert F. Kennedy's, and Edward M. Kennedy used it in his eulogy of Robert Kennedy.