MLA
Gonne, Maud, 1866-1953. Letter written by Maud Gonne to William Butler Yeats - May 4 [1911]. May 4, 1911. 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/180vq83dp7-cor.
APA, 6th edition
Gonne, Maud, 1866-1953. (May 4, 1911)[Letter written by Maud Gonne to William Butler Yeats - May 4 [1911]]. 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/180vq83dp7-cor.
Chicago
Gonne, Maud, 1866-1953, Letter written by Maud Gonne to William Butler Yeats - May 4 [1911], May 4, 1911, 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/180vq83dp7-cor.