MLA

Eliot, George, 1819-1880. Letter. Box 9. 1901 Apr 16. https://collections.library.yale.edu/catalog/32343967.

APA, 6th edition

Eliot, George, 1819-1880. (["Box 9"])(1901 Apr 16)[Letter]. https://collections.library.yale.edu/catalog/32343967.