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.

Biography

He was born in

Bloomsbury Bloomsbury is a district in the West End of London, part of the London Borough of Camden in England. It is considered a fashionable residential area, and is the location of numerous cultural institution, cultural, intellectual, and educational ...

London London is the Capital city, capital and List of urban areas in the United Kingdom, largest city of both England and the United Kingdom, with a population of in . London metropolitan area, Its wider metropolitan area is the largest in Wester ...

the eldest son of George Hadley of Osidge,

East Barnet East Barnet is an area of north London within the London Borough of Barnet bordered by New Barnet, Cockfosters and Southgate. It is a largely residential suburb whose central area contains shops, public houses, restaurants and services, and ...

Hertfordshire Hertfordshire ( or ; often abbreviated Herts) is a ceremonial county in the East of England and one of the home counties. It borders Bedfordshire to the north-west, Cambridgeshire to the north-east, Essex to the east, Greater London to the ...

and his wife Katherine FitzJames. His younger brother

George Hadley George Hadley (12 February 1685 – 28 June 1768) was an English lawyer and amateur meteorologist who proposed the atmospheric mechanism by which the trade winds are sustained, which is now named in his honour as Hadley circulation. As a key ...

became a noted

meteorologist A meteorologist is a scientist who studies and works in the field of meteorology aiming to understand or predict Earth's atmosphere of Earth, atmospheric phenomena including the weather. Those who study meteorological phenomena are meteorologists ...

. In 1717 John became a member (and later vice-president) of the

Royal Society of London The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, r ...

. In 1729 he inherited his father's East Barnet estate. He died in

in 1744 and is buried in the local churchyard with other members of his family. He had married Elizabeth, daughter of Thomas Hodges, FRS (former Attorney General of Barbados) and had one child, a son and heir John, born in 1738.

Work

In 1730 Hadley invented the reflecting octant, which could be 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. 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 In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...

. 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 telescope A reflecting telescope (also called a reflector) is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century by Isaac Newton as an alternati ...

s. In 1721 he showed the first parabolic

Newtonian telescope The Newtonian telescope, also called the Newtonian reflector or just a Newtonian, is a type of reflecting telescope invented by the English scientist Sir Isaac Newton, using a concave primary mirror and a flat diagonal secondary mirror. Newto ...

to the Royal Society. This Newtonian, with a

primary mirror A primary mirror (or primary) is the principal light-gathering surface (the objective) of a reflecting telescope. Description The primary mirror of a reflecting telescope is a spherical, parabolic, or hyperbolic shaped disks of polished ...

, compared favorably with the large aerial refracting telescopes of the day. He also made Gregorian telescopes with accurately shaped mirrors.

Honors

Mons Hadley and Rima Hadley on the

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

are named after him. The

Oasis Trust Oasis Charitable Trust, commonly known as Oasis, is a United Kingdom-based Christian registered charity. It was founded by the Reverend Steve Chalke in September of 1985. Chalke had been assistant minister at Tonbridge Baptist Church, Kent, for ...

Academy in

Ponders End Ponders End is the southeasternmost part of Enfield, London, Enfield, North London, north London, England, around Hertford Road west of the Lee Navigation, River Lee Navigation. It became Industrial suburb, industrialised through the 19th centur ...

in north London is called Oasis Academy Hadley in his honour.Oasis Academy in NE Enfield
Retrieved 5 February 2009

References

External links

Biography from the School of Mathematics and Statistics at the University of St Andrews, Scotland
{{DEFAULTSORT:Hadley, John 1682 births 1744 deaths People from Chipping Barnet 18th-century English astronomers 18th-century English inventors Fellows of the Royal Society People from Bloomsbury English scientific instrument makers

Biography

Work

Honors

See also

References

Further reading

External links