Born Enfield Chase, Hertfordshire, England, 16 April 1682
Died East Barnet, Hertfordshire, England, 14 February 1744
John Hadley made two major contributions to astronomy – the improvement in the reflecting telescope and the invention of the double‐reflecting quadrant. His brother George was the first (1735) to explain the direction of the trade winds as caused by the rotation of the Earth, superposed on an atmospheric circulation (called a Hadley cell) with an updraft near the Equator and downdrafts near latitudes 30° N and S.
Isaac Newton had used a spherical mirror in the telescope that he showed to the public, but he knew that a parabolic mirror would be much better. About 1720, John Hadley, with assistance from his brothers George and Henry, made a speculum mirror with a 15‐cm diameter, a focal length of about 157 cm, and a paraboloidal figure. The telescope was shown to the Royal Society in 1721. Edmond Halley, who had just become Astronomer Royal, and James Bradley, then...
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