MLA

Backus, Isaac, 1724-1806. Collected papers. box 8, folder 15. 1764 January-April, n.d.. https://collections.library.yale.edu/catalog/33555629.

APA, 6th edition

Backus, Isaac, 1724-1806. (["box 8, folder 15"])(1764 January-April, n.d.)[Collected papers]. https://collections.library.yale.edu/catalog/33555629.