Hadley's quadrant, 12 inch with back sight, early 19th century.
© Science Museum / Science & Society Picture Library
Navigational instrument made by Spencer, Browning and Rust. In 1716, John Hadley (1682-1744) became a Fellow of the Royal Society and was appointed vice-president in 1728. In 1730, he invented a quadrant which worked on a double-reflecting principle allowing an accurate measurement of the altitude of stars and the Sun. This instrument was the precursor of the sextant.