Albert Einstein (2016). “The Albert Einstein Collection: Essays in Humanism, The Theory of Relativity, and The World As I See It”, p.53, Open Road Media
Alexander Pope (1823). “An Essay on Man: In Four Epistles, to Henry St. John, Lord Bolingbroke : to which is Added, The Universal Prayer, with Other Poems”, p.33
Henry Ward Beecher (1887). “Beecher : Christian Philosopher, Pulpit Orator, Patriot and Philantropist: A Volume of Representative Selections from the Sermons, Lectures, Prayers, and Letters of Henry Ward Beecher”