1682-1744

English mathematician and instrument maker whose new grinding techniques made it possible for him to construct high quality reflecting telescopes. His first such instrument was constructed in 1721 and tested and praised by James Bradley and Edmond Halley. In 1730 he invented the reflecting quadrant. A priority dispute arose, but the convenience of Hadley's design for ship-board use made his the instrument of choice for navigators. His instrument evolved into the modern sextant.