A Mid 18th Century Brass Universal Equinoctial Ring Dial. This is a horological instrument for time telling made and signed by ‘B. Martin, London’. Benjamin Martin (1704-1782) was an 18th century English instrument maker considered one the greatest designers and manufacturers of his time. The dial consists of two rings and a bridging bar inside the outer ring. The outer ring is known as the meridian ring to represent a circle through the North and South celestial poles. It carries a 90-0-90 degree latitude scale on one side and a 0-90 degree latitude scale on the other, for measuring the height of the sun. The inner-hinged ring represents the celestial equator and is engraved with a double twelve-hour scale. The rotating bridging bar engraved with a calendar for the day of the month, is set at the poles of the meridian to represent the axis of the world and a slider with a pinhole is set between the bars of the bridge to act as the shadow marker. Diameter: 11.5 cm. (4.5 inches). Benjamin Martin was a prolific maker of scientific and optical instruments working from various addresses close to Fleet Street, London between 1738 & 1777. In 1764 he was a petitioner against Dolland's patent, he became bankrupt in 1782 and died in the same year. Reference: Hester Higton. Sundial. An Illustrated History of Portable Dials. Philip Wilson Pub. London. .