A circular brass case on four levelling feet covered with a reflecting but transparent glass plate working over spirits of wine. The space below the glass plate is filled with spirits by a detached brass funnel that fits in a tube at the side of the case, covered by a threaded stop. The case should be nearly filled, leaving an air bubble that works like a level. By levelling the instrument with the feet, the air bubble is brought under the centre of the glass, and the instrument is ready for use. The funnel is for replacing the spirits and for letting off pressure when the liquid has expanded due to warmth.

The artificial horizon is contained in a fitted shaped mahogany box, with printed instructions for using the instrument in the lid and a handwritten inscription, ‘Presented by R. Lionel Foster, Esq.’.