Sources: NBuU-PO
- Samuel L. Clemens to Charles Henry Webb, 8 April 1875 · Hartford, Conn · UCCL01219
- Samuel L. Clemens to Charles Casey, 15 May 1876 · Hartford, Conn · UCCL12172
- Samuel L. Clemens to Francis E. Bliss, 24 December 1880 · Hartford, Conn · UCCL01877
- SLC to J. M. G. Wood, 8 September 1886 · Elmira, N.Y · UCCL03453
- SLC to Andrew Chatto, 30 July 1897 · Weggis, Switzerland · UCCL05274
- SLC to Unidentified, 28 November 1902 · New York, N.Y · UCCL09371
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