Mark Twain, William Dean Howells (1960). “Mark Twain-Howells Letters: The Correspondence of Samuel L. Clemens and William D. Howells, 1872-1910”, Belknap Press
Mark Twain (1871). “The Innocents Abroad, Or, The New Pilgrims' Progress: Being Some Account of the Steamship Quaker City's Pleasure Excursion to Europe and the Holy Land : with Descriptions of Countries, Nations, Incidents and Adventures, as They Appeared to the Author”, p.239