Which aid to seafarers was invented in 1730 by John Hadley?
Hadley Upland Thomas Godfrey, independently invented the quadrant (the forerunner of the sextant), in 1730–31. Hadley Upland Hadley Upland () is a triangular shaped remnant plateau with an undulating surface, , in southern Graham Land, Antarctica. It is bounded by Windy Valley and Martin Glacier, Gibbs Glacier and Lammers Glacier. The existence of this upland was known to the United States Antarctic Service, 1939–41, Finn Ronne and Carl R. Eklund having travelled along Lammers and Gibbs Glaciers in January 1941. The upland was surveyed by the Falkland Islands Dependencies Survey in 1948–50 and 1958, and was named by the UK Antarctic Place-Names
John Hadley the local churchyard with other members of his family. He had married Elizabeth, daughter of Thomas Hodges, FRS (former Attorney General of Barbados) and had one child, a son and heir John, born in 1738. In 1730 Hadley invented the reflecting octant, which could be used to measure the altitude of the sun or other celestial objects above the horizon at sea. A mobile arm carrying a mirror and pivoting on a graduated arc provides a reflected image of the celestial body overlapping the image of the horizon, which is observed directly. If the position of the object on the