MLA

Ernest Augustus, King of Hanover, 1771-1851. Music book. Box 183, folder 946. circa 1819. https://collections.library.yale.edu/catalog/15832040.

APA, 6th edition

Ernest Augustus, King of Hanover, 1771-1851. (["Box 183, folder 946"])(circa 1819)[Music book]. https://collections.library.yale.edu/catalog/15832040.