L2157-005

Mural quadrant Long Caption: This 8ft Mural Quadrant was made for the second Astronomer Royal, Edmond Halley by (or under the direction of) instrument maker George Graham and was such a success that it became a prototype for similar instruments all over Europe. A mural quadrant is, as the name would suggest, a telescope mounted on a quarter circle frame which is then mounted on a wall aligned north-south so that the two sides or radii run vertical and horizontal. The telescope is pivoted at what would be the centre of the circle while the circle's circumference carries a scale from 0 to 90 degrees. This allows the observer to measure the angular height of the star he or she is observing. Telescope: The tube length is 8ft with an 8ft 0.5inch focus. Its object glass was replaced in 1789 replacing the common OG with an achromatic one. Mount: The mount is made up of an iron and mahogany frame with a brass scale divided into 96 parts by subdivision which could then be readjusted to produce a 0-90 degree angle scale. The scale was redivided by John Bird in 1753 and the quadrant remounted to face north instead of south. Credit line: © National Maritime Museum, Greenwich, London Object: AST0970 Artist: George Graham Date: 1725 Medium: iron Size: 2438 mm Click here to buy a bespoke print of this image.