MLA

Mason, William Smith, 1866-. Benjamin Franklin: letter to Joshua Babcock; Philadelphia. Box 61 (Oversize), folder 2274. 1763 November 10. https://collections.library.yale.edu/catalog/33490195.

APA, 6th edition

Mason, William Smith, 1866-. (["Box 61 (Oversize), folder 2274"])(1763 November 10)[Benjamin Franklin: letter to Joshua Babcock; Philadelphia]. https://collections.library.yale.edu/catalog/33490195.