MLA
Gonne, Maud, 1866-1953. Letter written by Maud Gonne to William Butler Yeats - [ca. May-June 1899]. June 1899 approx.. Maud Gonne and W.B. Yeats Papers, circa 1890-1938. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/1848pk0r4k-cor.
APA, 6th edition
Gonne, Maud, 1866-1953. (June 1899 approx.)[Letter written by Maud Gonne to William Butler Yeats - [ca. May-June 1899]]. Maud Gonne and W.B. Yeats Papers, circa 1890-1938, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/1848pk0r4k-cor.
Chicago
Gonne, Maud, 1866-1953, Letter written by Maud Gonne to William Butler Yeats - [ca. May-June 1899], June 1899 approx., Maud Gonne and W.B. Yeats Papers, circa 1890-1938, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/1848pk0r4k-cor.