Sources: UkLNAL
- SLC to William E. Baillie, 25 January 1874 · SS Parthia · UCCL09392 UkLNAL
- Samuel L. Clemens to William E. Baillie, 13 February 1874 · Hartford, Conn · UCCL01047 UkLNAL
- SLC to Henry Irving, 28 June 1897, London, England · UCCL14008 UkLNAL
- SLC to H. Walter Barnett, 25 October 1899 · London, England · UCCL05694 UkLNAL
1