MLA

Wolff, Kurt, 1887-1963. Das Perpetuum mobile. Box 7, folder 261-63. [1908?], 1910. https://collections.library.yale.edu/catalog/11238557.

APA, 6th edition

Wolff, Kurt, 1887-1963. (["Box 7, folder 261-63"])([1908?], 1910)[Das Perpetuum mobile]. https://collections.library.yale.edu/catalog/11238557.