MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 75, folder 1591-1596. 1940 Jun-Aug. https://collections.library.yale.edu/catalog/2043467.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 75, folder 1591-1596"])(1940 Jun-Aug)[Letters]. https://collections.library.yale.edu/catalog/2043467.