MLA

Nicholls, Norton, 1741?-1809. Charles de Bonstetten to Norton Nicholls. Bern. Concerns B. Tscharner; Cambridge University. Box 2, folder 196. 1773 May 1. https://collections.library.yale.edu/catalog/17439993.

APA, 6th edition

Nicholls, Norton, 1741?-1809. (["Box 2, folder 196"])(1773 May 1)[Charles de Bonstetten to Norton Nicholls. Bern. Concerns B. Tscharner; Cambridge University]. https://collections.library.yale.edu/catalog/17439993.