Sources: MoHi
- SLC to Daniel Slote, 31 March 1881 · Hartford, Conn · UCCL01933 MoHi
- SLC to Florence Hayward, 29 October 1896 · London, England · UCCL05139 MoHi
- SLC to Florence Hayward, 29 January 1897 · London, England · UCCL05174 MoHi
- SLC to Florence Hayward, 3 July 1897 · London, England · UCCL05255 MoHi
- SLC to Bertha von Suttner, 17 February 1898 · Vienna, Austria · UCCL05351 MoHi
- SLC to Bertha von Suttner, 27 March 1899 · Budapest, Hungary · UCCL05569 MoHi
- SLC to Florence Hayward, 6 July 1901 · Saranac Lake, N.Y · UCCL06085 MoHi
- SLC to George Iles, 26 May 1902 · Riverdale, N.Y · UCCL06346 MoHi
- Henry W. Fischer to SLC, 2 June 1902 · UCLC50334 MoHi
- SLC per Isabel V. Lyon to George F. Mockler, 1‒31 December 1902 · Riverdale, N.Y · UCCL06535 MoHi
- SLC to Unidentified, 4 January 1909 · New York, N.Y · UCCL08309 MoHi
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