MLA

Nicholls, Norton, 1741?-1809. Norton Nicholls to Jane Floyer Nicholls. Milan. Concerns Count Charles Firmian; Horace Mann. Box 2, folder 134. 1772 Feb 8. https://collections.library.yale.edu/catalog/17439931.

APA, 6th edition

Nicholls, Norton, 1741?-1809. (["Box 2, folder 134"])(1772 Feb 8)[Norton Nicholls to Jane Floyer Nicholls. Milan. Concerns Count Charles Firmian; Horace Mann]. https://collections.library.yale.edu/catalog/17439931.