John Hadley

John Hadley was an English mathematician and instrument maker who served as vice president of the Royal Society. In 1730 he invented the reflecting octant, the direct ancestor of the sextant, independently of the American instrument maker Thomas Godfrey, who built a working octant on the same double reflection principle at approximately the same time, so credit for the invention is shared between them. Hadley also ground and figured the first successful parabolic mirrors for reflecting telescopes, demonstrating a Newtonian telescope to the Royal Society in 1721.