MLA

Nicholls, Norton, 1741?-1809. Charles de Bonstetten to Norton Nicholls. Bern. Concerns Bern, Switzerland; Norton Nicholls. Box 2, folder 136. [1772] Feb 10. https://collections.library.yale.edu/catalog/17439933.

APA, 6th edition

Nicholls, Norton, 1741?-1809. (["Box 2, folder 136"])([1772] Feb 10)[Charles de Bonstetten to Norton Nicholls. Bern. Concerns Bern, Switzerland; Norton Nicholls]. https://collections.library.yale.edu/catalog/17439933.