"The 100 best nonfiction books: No 68 - Narrative of the Life of Frederick Douglass, an American Slave by Frederick Douglass (1845)" by Robert McCrum, www.theguardian.com. May 22, 2017.
Albert Einstein (2015). “Bite-Size Einstein: Quotations on Just About Everything from the Greatest Mind of the Twentieth Century”, p.52, St. Martin's Press