Astronomical and navigational instruments, Compasses

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Dry card compass

ACO0005
Astronomical and navigational instruments

Object connections:

Collection Astronomical and navigational instruments, Compasses
User collections Longitude punk'd by hfinch-boyer
Gallery locationNot on display

Object details:

Object ID ACO0005
Description Azimuth compasses are used for taking bearings from a ship. They therefore have vertical sights on top and the compass card is divided into degrees as well as the points of the compass. This example is a dry card compass. Each quarter of the card is divided from 0 to 90 degrees, with 0 at the north and south points. The numbers are printed in reverse, so that they can be read when viewed through the prismatic sight. The card is also marked with eight points. The compass needle is attached to the underside of the card and is lozenge-shaped. The card is pivoted on a steel pin that is attached to the bottom of the bowl. A movable horizon ring is fitted to the top of the bowl. This has two sights, with shades (green and red) on the fore sight and a movable shade for the back sight. The compass bowl is held on gimbals, which allow it to remain level, and has a lever mechanism to steady the compass card when taking a bearing. The maker’s name is printed on the card as ‘W&T. GILBERT, 148, Leadenhall St. LONDON’ and the date ‘19 April 1838’ is handwritten on the underside of the card. This was probably the date when it was examined by the Admiralty Compass Committee. The number ‘H.83’ is also inscribed on the gimbal ring.
Date made 1838

Artist/Maker Gilbert & Sons
Place made London
Credit National Maritime Museum, Greenwich, London, Admiralty Compass Observatory
Materials card; glass; lead; wood; brass
Measurements Overall: 300 mm; Diameter: 225 mm; Weight: 5.9 kg
Parts
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