John Hadley
Encyclopedia
- This article is about John Hadley, the mathematician. For John Hadley the chemist (1731–1764) see John Hadley (chemist)John Hadley (chemist)John Hadley was a British chemist and physician.John Hadley was appointed in 1756 as the fourth Professor of Chemistry at Cambridge University, the oldest continuously occupied chair of Chemistry in the UK. During his time there he co-operated in 1758 with Benjamin Franklin on a series of...
John Hadley (16 April 1682 – 14 February 1744) was an English
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
mathematician, inventor of the octant
Octant (instrument)
The octant, also called reflecting quadrant, is a measuring instrument used primarily in navigation. It is a type of reflecting instrument.-Etymology:...
, a precursor to the sextant
Sextant
A sextant is an instrument used to measure the angle between any two visible objects. Its primary use is to determine the angle between a celestial object and the horizon which is known as the altitude. Making this measurement is known as sighting the object, shooting the object, or taking a sight...
, around 1730.
He was born in Bloomsbury
Bloomsbury
-Places:* Bloomsbury is an area in central London.* Bloomsbury , related local government unit* Bloomsbury, New Jersey, New Jersey, USA* Bloomsbury , listed on the NRHP in Maryland...
, London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...
, to Katherine FitzJames and George Hadley
George Hadley
George Hadley was an English lawyer and amateur meteorologist who proposed the atmospheric mechanism by which the Trade Winds are sustained. As a key factor in ensuring that European sailing vessels reached North American shores, understanding the Trade Winds was becoming a matter of great...
.
In 1717 he became a member (and later vice-president) of the Royal Society of London. On 6 June 1734 he married Elizabeth Hodges who herself was wealthy. They had one child, a son John born in 1738.
The octant is used to measure the altitude of the Sun or other celestial
Celestial sphere
In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with the Earth and rotating upon the same axis. All objects in the sky can be thought of as projected upon the celestial sphere. Projected upward from Earth's equator and poles are the...
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
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
. The octant proved extremely valuable for navigation and displaced the use of other instruments such as the Davis quadrant.
An American
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, Thomas Godfrey
Thomas Godfrey (inventor)
Thomas Godfrey was an optician and inventor in the American colonies, who around 1730 invented the octant. At approximately the same time an Englishman, John Hadley, also invented the octant independently....
, independently invented the octant at approximately the same time.
Hadley also developed ways to make precision aspheric and parabolic
Parabolic reflector
A parabolic reflector is a reflective device used to collect or project energy such as light, sound, or radio waves. Its shape is that of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis...
objective
Objective (optics)
In an optical instrument, the objective is the optical element that gathers light from the object being observed and focuses the light rays to produce a real image. Objectives can be single lenses or mirrors, or combinations of several optical elements. They are used in microscopes, telescopes,...
mirrors for reflecting telescope
Reflecting telescope
A reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the refracting telescope which, at that time, was a design that suffered from...
s. In 1721 he showed the first parabolic Newtonian telescope
Newtonian telescope
The Newtonian telescope is a type of reflecting telescope invented by the British scientist Sir Isaac Newton , using a concave primary mirror and a flat diagonal secondary mirror. Newton’s first reflecting telescope was completed in 1668 and is the earliest known functional reflecting telescope...
to the Royal Society. This Newtonian, with a 6 inches (152.4 mm) primary mirror
Primary mirror
A primary mirror is the principal light-gathering surface of a reflecting telescope.-Description:The primary mirror of a reflecting telescope is a spherical or parabolic shaped disks of polished reflective metal , or in later telescopes, glass or other material coated with a reflective layer...
, compared favorably with the large aerial refracting telescopes
Aerial telescope
An aerial telescope is a type of very-long-focal-length refracting telescope built in the second half of the 17th century that did not use a tube. Instead, the objective was mounted on a pole, tree, tower, building or other structure on a swivel ball-joint. The observer stood on the ground and held...
of the day. He also made Gregorian telescope
Gregorian telescope
The Gregorian telescope is a type of reflecting telescope designed by Scottish mathematician and astronomer James Gregory in the 17th century, and first built in 1673 by Robert Hooke...
s with accurately shaped mirrors.
Hadley died in East Barnet
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, known locally as the Village, contains a variety of shops, public houses, restaurants and services. East Barnet is...
, Hertfordshire
Hertfordshire
Hertfordshire is a ceremonial and non-metropolitan county in the East region of England. The county town is Hertford.The county is one of the Home Counties and lies inland, bordered by Greater London , Buckinghamshire , Bedfordshire , Cambridgeshire and...
, in 1744.
Mons Hadley
Mons Hadley
Mons Hadley is a massif in the northern portion of the Montes Apenninus, a range in the northern hemisphere of the Moon. The selenographic coordinates of this peak are 26.5° N, 4.7° E. It has a height of 4.6 km and a maximum diameter of 25 km at the base.To the southwest of this mountain...
and Rima Hadley on the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
are named after him.
The Oasis Trust
Oasis Trust
Oasis Trust is a UK-based Christian registered charity. It was founded by Rev Steve Chalke in August 1985, who had been assistant minister at Tonbridge Baptist Church, Kent, for four years...
Academy in Enfield Wash
Enfield Wash
Enfield Wash is an area in the London Borough of Enfield, North London. It is approximately located in the area either side of Hertford Road between Turkey Street and Albany Road.- Etymology :...
is called Oasis Academy Hadley
Oasis Academy Hadley
Oasis Academy Hadley is an Academy in Enfield, England run by Oasis Community Learning. It is the second academy in Enfield and has close links with Oasis Academy Enfield. It opened on 7 September 2009...
in his honour.
He is the older brother of George Hadley
George Hadley
George Hadley was an English lawyer and amateur meteorologist who proposed the atmospheric mechanism by which the Trade Winds are sustained. As a key factor in ensuring that European sailing vessels reached North American shores, understanding the Trade Winds was becoming a matter of great...
(meteorologist).