MLA
Forbes, A. Letter from A. Forbes (Farmington, Van Buren County, Iowa) to His Son, Belvin, Discusses Politics and Economic Problems of the Period - December 9, 1863 (Typescript). 1863. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 19, Folder 24. https://digital.library.emory.edu/purl/890rr4xj2r-cor.
APA, 6th edition
Forbes, A. (1863). Letter from A. Forbes (Farmington, Van Buren County, Iowa) to his son, Belvin, discusses politics and economic problems of the period - December 9, 1863 (typescript) (Box 19, Folder 24) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/890rr4xj2r-cor.
Chicago
Forbes, A. “Letter from A. Forbes (Farmington, Van Buren County, Iowa) to His Son, Belvin, Discusses Politics and Economic Problems of the Period - December 9, 1863 (Typescript).” Letters (correspondence). Civil War Collection, 1863. Box 19, Folder 24. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/890rr4xj2r-cor.