MLA
Downs, J. T. Letter from J. T. Downs (in a Field near Atlanta, Georgia) to Mrs. N. Dudley - July 25, 1864. 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 3, Folder 9. https://digital.library.emory.edu/purl/153jwstrkh-cor.
APA, 6th edition
Downs, J. T. (1864). Letter from J. T. Downs (in a field near Atlanta, Georgia) to Mrs. N. Dudley - July 25, 1864 (Box 3, Folder 9) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/153jwstrkh-cor.
Chicago
Downs, J. T. “Letter from J. T. Downs (in a Field near Atlanta, Georgia) to Mrs. N. Dudley - July 25, 1864.” Letters (correspondence). Civil War Collection, 1864. Box 3, Folder 9. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/153jwstrkh-cor.