Henry David Thoreau (2014). “Citizen Thoreau: Walden, Civil Disobedience, Life Without Principle, Slavery in Massachusetts, A Plea for Captain John Brown”, p.134, Graphic Arts Books
United States. President (1929-1933 : Hoover), Herbert Hoover (1974). “Herbert Hoover: Containing the Public Messages, Speeches, and Statements of the President”