MLA

Eliot, George, 1819-1880. Letter. Box 9. [1882] Aug 13. https://collections.library.yale.edu/catalog/32368874.

APA, 6th edition

Eliot, George, 1819-1880. (["Box 9"])([1882] Aug 13)[Letter]. https://collections.library.yale.edu/catalog/32368874.