MLA
Gonne, Maud, 1866-1953. Letter written by Maud Gonne to William Butler Yeats - September 27 [1909]. September 27, 1909. 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/549g4f4szq-cor.
APA, 6th edition
Gonne, Maud, 1866-1953. (September 27, 1909)[Letter written by Maud Gonne to William Butler Yeats - September 27 [1909]]. 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/549g4f4szq-cor.
Chicago
Gonne, Maud, 1866-1953, Letter written by Maud Gonne to William Butler Yeats - September 27 [1909], September 27, 1909, 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/549g4f4szq-cor.