MLA

Wordsworth, William, 1770-1850. [Letter : William Wordsworth to Biggs and Cottle]. Folder: Letter 13. 1800 December 23. https://collections.library.yale.edu/catalog/16169072.

APA, 6th edition

Wordsworth, William, 1770-1850. (["Folder: Letter 13"])(1800 December 23)[[Letter : William Wordsworth to Biggs and Cottle]]. https://collections.library.yale.edu/catalog/16169072.