MLA

Fisher, Alexander Metcalf, 1794-1822. Fisher, Alexander Metcalf to Princeton University. Box 1, folder 21. 1821-10-19. https://collections.library.yale.edu/catalog/17454598.

APA, 6th edition

Fisher, Alexander Metcalf, 1794-1822. (["Box 1, folder 21"])(1821-10-19)[Fisher, Alexander Metcalf to Princeton University]. https://collections.library.yale.edu/catalog/17454598.