John Hadley
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| John Hadley | |
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John Hadley
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| Born | 16 April 1682 1682 Bloomsbury, London |
| Died | Script error: The function "death_date_and_age" does not exist. East Barnet, Hertfordshire |
| Nationality | English |
| Known for | octant |
John Hadley (16 April 1682 – 14 February 1744) was an English mathematician, and laid claim to the invention of the octant, two years after Thomas Godfrey claimed the same.[1]
Biography
He was born in Bloomsbury, London. In 1717 he became a member (and later vice-president) of the Royal Society of London. Hadley died in East Barnet, Hertfordshire, in 1744.
Work
The octant is used to measure the altitude of the sun or other celestial objects above the horizon at sea. A mobile arm carrying a mirror and pivoting on a graduated arc provides a reflected image of the celestial body overlapping the image of the horizon, which is observed directly.[2] If the position of the object on the sky and the time of the observation are known, it is easy for the user to calculate his own latitude. The octant proved extremely valuable for navigation and displaced the use of other instruments such as the Davis quadrant. An American, Thomas Godfrey, independently invented the octant at approximately the same time.
Hadley also developed ways to make precision aspheric and parabolic objective mirrors for reflecting telescopes. In 1721 he showed the first parabolic Newtonian telescope to the Royal Society.[3] This Newtonian, with a 6-inch-diameter (150 mm) primary mirror, compared favorably with the large aerial refracting telescopes of the day.[4] He also made Gregorian telescopes with accurately shaped mirrors.[5][6]
Honors
Mons Hadley and Rima Hadley on the Moon are named after him. The Oasis Trust Academy in Ponders End is called Oasis Academy Hadley in his honour.[7]
Family
His parents were Katherine FitzJames and George Hadley. His younger brother George Hadley was a noted meteorologist. On 6 June 1734 he married Elizabeth Hodges who herself was wealthy. They had one child, a son John born in 1738.
References
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Institute and Museum of the History of Science, Florence, Italy: Picture of Hadley's octant [1]
- ↑ amazing-space.stsci.edu - Hadley’s Reflector
- ↑ The complete Amateur Astronomer - John Hadley's Reflector
- ↑ Henry C. King - The history of the telescope - page 77
- ↑ telescopeѲptics.net - 8.2. Two-mirror telescopes
- ↑ Oasis Academy in NE Enfield Retrieved 5 February 2009
External links
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Wikisource has the text of a 1920 Encyclopedia Americana article about John Hadley. |
