Artificial mercury horizon with fitted leather carrying case, designed by Captain Christopher, provisionally patented in 1868 (No.2624), by the company of William Cary, 1868-1875. Consists of two black-lacquered steel mercury holders on three levelling feet, interconnected by a tube fitted with a stopcock. One is a storage reservoir with a valve to admit air and empty the mercury into the other, which is used for making observations and is fitted with a glass cover. A spare glass cover in a chamois leather pouch, and a lever pin for operating the stopcock (both stored in the glass-covered reservoir).