MLA

Eliot, George, 1819-1880. Letter. Box 10. 1919 Apr 2. https://collections.library.yale.edu/catalog/32365697.

APA, 6th edition

Eliot, George, 1819-1880. (["Box 10"])(1919 Apr 2)[Letter]. https://collections.library.yale.edu/catalog/32365697.