John Hadley, English inventor
{"Image ImageDescription": "John Hadley (1682-1744), English inventor. In the 1720s Hadley improved Newton's reflecting telescope of 1668. As a result of Hadley's work, this type of telescope subsequently dominated optical astronomy. In 1731 Hadley made a reflecting quadrant which could accurately measure the position of a star above the horizon. This forerunner of the sextant was used in conjunction with chronometers and astronomical tables to discover a ship's position. Hadley was voted a Fellow of the Royal Society in 1717 and became one of its vice-presidents in 1728.", "Image XResolution": "72", "Image YResolution": "72", "Image ResolutionUnit": "Pixels/Inch", "Image YCbCrPositioning": "Centered", "Image Copyright": "Science Photo Library"}