John Hadley (1682-1744) was a natural philosopher and mathematician. He was elected a fellow of the Royal Society in 1717 and invented the navigational instrument known as the octant, or Hadley’s quadrant.
Reference:
Gloria Clifton, ‘Hadley, John (1682-1744)’, Oxford Dictionary of National Biography, Oxford University Press, (2004; online edn, Jan 2008 http://www.oxforddnb.com/view/article/11860 [accessed 16 July 2013]).
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