MLA

Speck, William A. (William Alfred), 1864-1928. ALS : Jena, to Johann Wolfgang von Goethe?. Box 10, folder 347. 1781 Aug 17. https://collections.library.yale.edu/catalog/16738552.

APA, 6th edition

Speck, William A. (William Alfred), 1864-1928. (["Box 10, folder 347"])(1781 Aug 17)[ALS : Jena, to Johann Wolfgang von Goethe?]. https://collections.library.yale.edu/catalog/16738552.