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Bennett, J. and Johnston, S., The Geometry of War, 1500-1750 (Oxford, 1996)

36. A perpendicular enabled a gunner to establish the centre line of an artillery piece and thus its direction of fire. The instrument was placed transversely on the gun's barrel and, once levelled using the spirit level, the steel plunger was depressed. Marks were made at the muzzle and breech of the gun and joined by a chalk line. Perpendiculars incorporating spirit levels were first purchased by the English Office of Ordnance in 1757 and replaced earlier versions in which the levelling was carried out with a plumb bob and line (Millburn 1995, p. 35).

The instrument has a shaped, fishskin-covered case of wood and pasteboard.

Height: 115 mm

Inventory no. 51,485

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