Albert Einstein (2015). “Bite-Size Einstein: Quotations on Just About Everything from the Greatest Mind of the Twentieth Century”, p.31, St. Martin's Press
Neil Armstrong's letter to the children of Troy, Michigan on the opening of its Public Library (1971), as quoted in "Why Libraries Matter: Letters to the Children of Troy, Michigan (From 1971)" by Lucas Reilly on Mental Floss, July 3, 2012.