MLA

Sectional View of the Observatory Erected over the Cross of St. Paul's Cathedral by Mr. Thos. Hornor [Graphic]. publisher not identified, 0AD. https://collections.library.yale.edu/catalog/33223574.

APA, 6th edition

Sectional view of the observatory erected over the cross of St. Paul's Cathedral by Mr. Thos. Hornor [graphic]. (0 C.E.). [Crosses, Lithographs England London 1849]. publisher not identified. https://collections.library.yale.edu/catalog/33223574.