Two black-lacquered steel reservoirs on three levelling feet, and inter-connected by a tube fitted with a stopcock. One reservoir is for storing the mercury; the other has a removable clear glass cover. For an observation the mercury is let into the glass-covered reservoir. The storage reservoir is provided with a valve to admit air or allow it to escape. Accompanying the instrument are a spare glass cover in a chamois leather pouch and a lever pin for operating the stopcock.

The artificial horizon is contained in a fitted leather carrying case.

Christopher George (1809-87) provisionally patented this horizon (no. 2624 of 1868). In his ‘Description’ he states that only H. Porter, Strand in London manufactured it. Henry Porter had been an apprentice to William Cary, and C&P is the trademark for Cary and Porter. George received a medal at the International Geographical Congress of Paris, 1875 for this horizon and for his double box sextant NAV1118.