MLA

Stieglitz, Alfred, 1864-1946. Letter. Box 84, folder 1705. 1927 Aug 6. https://collections.library.yale.edu/catalog/2039728.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 84, folder 1705"])(1927 Aug 6)[Letter]. https://collections.library.yale.edu/catalog/2039728.