Hadley's Economics: An Account of the Relations between Private Property and Public Welfare (1896).
The mariner's astrolabe was superseded by John Hadley's quadrant of 1731.
Focal length presented to the Royal Society by Huygens, and found that Hadley's reflector "will bear such a charge as to make it magnify the object as many times as the latter with its due charge, and that it represents objects as distinct, though not altogether so clear and bright....
(1760); " A Recommendation of Hadley's Quadrant for Surveying," ibid.
He also invented a reflecting sextant for observing the distance between the moon and the fixed stars, - the same in every essential as the instrument which is still in everyday use at sea under the name of Hadley's quadrant.