MLA

Nicholls, Norton, 1741?-1809. Thomas Gray to Norton Nicholls. Cambridge University. Concerns Charles de Bonstetten. Box 1, folder 90. 1770 Mar 20. https://collections.library.yale.edu/catalog/17439887.

APA, 6th edition

Nicholls, Norton, 1741?-1809. (["Box 1, folder 90"])(1770 Mar 20)[Thomas Gray to Norton Nicholls. Cambridge University. Concerns Charles de Bonstetten]. https://collections.library.yale.edu/catalog/17439887.