Ralph Waldo Emerson, Robert Ernest Spiller, Alfred Riggs Ferguson, Joseph Slater, Jean Ferguson Carr (1971). “The Collected Works of Ralph Waldo Emerson: Nature, addresses, and lectures”, p.9, Harvard University Press
Ralph Waldo Emerson, Robert Ernest Spiller, Alfred Riggs Ferguson, Joseph Slater, Jean Ferguson Carr (1971). “The Collected Works of Ralph Waldo Emerson: Nature, addresses, and lectures”, p.9, Harvard University Press
Albert Einstein (2015). “Bite-Size Einstein: Quotations on Just About Everything from the Greatest Mind of the Twentieth Century”, p.15, St. Martin's Press