Richard Strauss, Stefan Zweig (1977). “A Confidential Matter: The Letters of Richard Strauss and Stefan Zweig, 1931-1935”, p.39, Univ of California Press
Henry Wadsworth Longfellow (1888). “Longfellow's Days: The Longfellow Prose Birthday Book : Extracts from the Journals and Letters of H. W. Longfellow”