MLA

Hilles, Frederick W. (Frederick Whiley), 1900-1975. Carlyle, Thomas. Box 23, folder 732. 1865 April 21. https://collections.library.yale.edu/catalog/10516125.

APA, 6th edition

Hilles, Frederick W. (Frederick Whiley), 1900-1975. (["Box 23, folder 732"])(1865 April 21)[Carlyle, Thomas]. https://collections.library.yale.edu/catalog/10516125.