Richard Strauss, Stefan Zweig (1977). “A Confidential Matter: The Letters of Richard Strauss and Stefan Zweig, 1931-1935”, p.67, Univ of California Press
"The History of Freedom in Antiquity". Lord Acton's opening statement of his speech on February 28, 1877; later quoted in "The History of Freedom and Other Essays" edited by John Neville Figgis and Reginald Vere Laurence, 1907.