MLA

Gibbs, J. Willard (Josiah Willard), 1839-1903. Autograph letter, signed, (draft) to [Pierre Maurice Maire Duhem]. New Haven.. Box 1, folder 10. 1887 February 2. https://collections.library.yale.edu/catalog/17296910.

APA, 6th edition

Gibbs, J. Willard (Josiah Willard), 1839-1903. (["Box 1, folder 10"])(1887 February 2)[Autograph letter, signed, (draft) to [Pierre Maurice Maire Duhem]. New Haven.]. https://collections.library.yale.edu/catalog/17296910.