MLA

Stieglitz, Alfred, 1864-1946. Letter : Lake George, to A[nanda Kentish] C[oomaraswamy]. Box 1, folder 3. [19]24 Aug 3. https://collections.library.yale.edu/catalog/32500210.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 1, folder 3"])([19]24 Aug 3)[Letter : Lake George, to A[nanda Kentish] C[oomaraswamy]]. https://collections.library.yale.edu/catalog/32500210.