The Columbia Encyclopedia, Sixth Edition. 2001-07.
Hadley, John
16821744, English instrument maker. An optician by trade, Hadley built reflecting telescopes, based on Newtons model, that had greater resolution than the cumbersome refractors then in use. In 1731 he built a reflecting octant, based on Newtons sketch, that prefigured the modern nautical sextant. Hadley was a leading member of the Royal Society.