United States. President (1929-1933 : Hoover), Herbert Hoover, United States. Office of the Federal Register (1974). “Herbert Hoover: Containing the public messages, speeches, and statements of the President”
Thomas Jefferson, H. A. Washington (2011). “The Writings of Thomas Jefferson: Being His Autobiography, Correspondence, Reports, Messages, Addresses, and Other Writings, Official and Private”, p.40, Cambridge University Press
Louis O. Kelso, Patricia Hetter Kelso (1967). “Two-factor Theory: the Economics of Reality; how to Turn Eighty Million Workers Into Capitalists on Borrowed Money, and Other Proposals”, New York : Vintage Books