MLA

Bowen, Thomas, d. 1790, Speer, Joseph Smith., creator. To His Royal Highness. George Augustus Frederick. Prince of Wales &c. &c. &c. this chart of the West Indies is humbly inscribed by His Royal Highness faithful & obedient servant Joseph Smith Speer, Thos. Bowen sculpt. 1774 May 20. https://collections.library.yale.edu/catalog/2046638.

APA, 6th edition

Bowen, Thomas, d. 1790, & Speer, Joseph Smith., creator. (1774 May 20)[To His Royal Highness. George Augustus Frederick. Prince of Wales &c. &c. &c. this chart of the West Indies is humbly inscribed by His Royal Highness faithful & obedient servant Joseph Smith Speer, Thos. Bowen sculpt]. https://collections.library.yale.edu/catalog/2046638.