John Hadley

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John Hadley
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John Hadley
Born(1682-04-16)16 April 1682
Bloomsbury, London
Died14 February 1744(1744-02-14) (aged 61)
East Barnet, Hertfordshire
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]

England Country in north-west Europe, part of the United Kingdom

England is a country that is part of the United Kingdom. It shares land borders with Wales to the west and Scotland to the north-northwest. The Irish Sea lies west of England and the Celtic Sea lies to the southwest. England is separated from continental Europe by the North Sea to the east and the English Channel to the south. The country covers five-eighths of the island of Great Britain, which lies in the North Atlantic, and includes over 100 smaller islands, such as the Isles of Scilly and the Isle of Wight.

Octant (instrument) measuring instrument used primarily in navigation; type of reflecting instrument

The octant, also called reflecting quadrant, is a measuring instrument used primarily in navigation. It is a type of reflecting instrument.

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.



He was born in Bloomsbury, London the eldest son of George Hadley of Enfield Chase near East Barnet, Hertfordshire and his wife Katherine FitzJames. His younger brother George Hadley became a noted meteorologist.

Bloomsbury area of the London Borough of Camden, in London, England, UK

Bloomsbury is a district in the West End of London, famed as a fashionable residential area and as the home of numerous prestigious cultural, intellectual, and educational institutions. It is bounded by Fitzrovia to the west, Covent Garden to the south, Regent's Park and St. Pancras to the north, and Clerkenwell to the east.

London Capital of the United Kingdom

London is the capital and largest city of both England and the United Kingdom. Standing on the River Thames in the south-east of England, at the head of its 50-mile (80 km) estuary leading to the North Sea, London has been a major settlement for two millennia. Londinium was founded by the Romans. The City of London, London's ancient core − an area of just 1.12 square miles (2.9 km2) and colloquially known as the Square Mile − retains boundaries that follow closely its medieval limits. The City of Westminster is also an Inner London borough holding city status. Greater London is governed by the Mayor of London and the London Assembly.

East Barnet area of North London within the London Borough of 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 the parish church of St Mary the Virgin. East Barnet is close to the M25 and the A1 and M1.

In 1717 John became a member (and later vice-president) of the Royal Society of London. In 1729 he inherited his father's East Barnet estate. [2]

He died in East Barnet 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.


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. [3] 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.

Celestial sphere imaginary sphere of arbitrarily large radius, concentric with the observer

In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, which may be centered on Earth or the observer. If centered on the observer, half of the sphere would resemble a hemispherical screen over the observing location.

Latitude The angle between zenith at a point and the plane of the equator

In geography, latitude is a geographic coordinate that specifies the north–south position of a point on the Earth's surface. Latitude is an angle which ranges from 0° at the Equator to 90° at the poles. Lines of constant latitude, or parallels, run east–west as circles parallel to the equator. Latitude is used together with longitude to specify the precise location of features on the surface of the Earth. On its own, the term latitude should be taken to be the geodetic latitude as defined below. Briefly, geodetic latitude at a point is the angle formed by the vector perpendicular to the ellipsoidal surface from that point, and the equatorial plane. Also defined are six auxiliary latitudes which are used in special applications.

United States Federal republic in North America

The United States of America (USA), commonly known as the United States or America, is a country composed of 50 states, a federal district, five major self-governing territories, and various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is slightly smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U.S. is the third most populous country. The capital is Washington, D.C., and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico. The State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean. The U.S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The extremely diverse geography, climate, and wildlife of the United States make it one of the world's 17 megadiverse countries.

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. [4] This Newtonian, with a 6-inch-diameter (150 mm) primary mirror, compared favorably with the large aerial refracting telescopes of the day. [5] He also made Gregorian telescopes with accurately shaped mirrors. [6] [7]

Parabolic reflector reflector that has the shape of a parabola

A parabolicreflector is a reflective surface used to collect or project energy such as light, sound, or radio waves. Its shape is part of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis. The parabolic reflector transforms an incoming plane wave traveling along the axis into a spherical wave converging toward the focus. Conversely, a spherical wave generated by a point source placed in the focus is reflected into a plane wave propagating as a collimated beam along the axis.

Objective (optics) optical element that gathers light from the object being observed and focuses the light rays to produce a real image

In optical engineering, 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 a single lens or mirror, or combinations of several optical elements. They are used in microscopes, telescopes, cameras, slide projectors, CD players and many other optical instruments. Objectives are also called object lenses, object glasses, or objective glasses.

Reflecting telescope telescopes that reflect light with a combination of mirrors

A reflecting telescope 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 alternative to the refracting telescope which, at that time, was a design that suffered from severe chromatic aberration. Although reflecting telescopes produce other types of optical aberrations, it is a design that allows for very large diameter objectives. Almost all of the major telescopes used in astronomy research are reflectors. Reflecting telescopes come in many design variations and may employ extra optical elements to improve image quality or place the image in a mechanically advantageous position. Since reflecting telescopes use mirrors, the design is sometimes referred to as a "catoptric" telescope.


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. [8]

See also

Related Research Articles

Sextant angle measurement instrument

A sextant is a doubly reflecting navigation instrument that measures the angular distance between two visible objects. The primary use of a sextant is to measure the angle between an astronomical object and the horizon for the purposes of celestial navigation. The estimation of this angle, the altitude, is known as sighting or shooting the object, or taking a sight. The angle, and the time when it was measured, can be used to calculate a position line on a nautical or aeronautical chart—for example, sighting the Sun at noon or Polaris at night to estimate latitude. Sighting the height of a landmark can give a measure of distance off and, held horizontally, a sextant can measure angles between objects for a position on a chart. A sextant can also be used to measure the lunar distance between the moon and another celestial object in order to determine Greenwich Mean Time and hence longitude. The principle of the instrument was first implemented around 1731 by John Hadley (1682–1744) and Thomas Godfrey (1704–1749), but it was also found later in the unpublished writings of Isaac Newton (1643–1727). Additional links can be found to Bartholomew Gosnold (1571–1607) indicating that the use of a sextant for nautical navigation predates Hadley's implementation. In 1922, it was modified for aeronautical navigation by Portuguese navigator and naval officer Gago Coutinho.

History of the telescope aspect of history

The earliest known telescope appeared in 1608 in the Netherlands when an eyeglass maker named Hans Lippershey tried to obtain a patent on one. Although Lippershey did not receive his patent, news of the new invention soon spread across Europe. The design of these early refracting telescopes consisted of a convex objective lens and a concave eyepiece. Galileo improved on this design the following year and applied it to astronomy. In 1611, Johannes Kepler described how a far more useful telescope could be made with a convex objective lens and a convex eyepiece lens and by 1655 astronomers such as Christiaan Huygens were building powerful but unwieldy Keplerian telescopes with compound eyepieces.

Newtonian telescope

The Newtonian telescope, also called the Newtonian reflector or just the Newtonian, is a type of reflecting telescope invented by the English scientist Sir Isaac Newton (1642–1727), 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. The Newtonian telescope's simple design makes it very popular with amateur telescope makers.

Speculum metal

Speculum metal is a mixture of around two-thirds copper and one-third tin making a white brittle alloy that can be polished to make a highly reflective surface. It was used historically to make different kinds of mirrors from personal grooming aids to reflecting telescope optical mirrors until it was replaced by more modern materials.

Andrew Ainslie Common British astronomer

Andrew Ainslie Common FRS (1841–1903) was an English amateur astronomer best known for his pioneering work in astrophotography.

Cassegrain reflector type of telescope reflector

The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas, the main characteristic being that the optical path folds back onto itself, relative to the optical system's primary mirror entrance aperture. This design puts the focal point at a convenient location behind the primary mirror and the convex secondary adds a telephoto effect creating a much longer focal length in a mechanically short system.

Schmidt–Newton telescope

A Schmidt–Newton telescope or Schmidt–Newtonian telescope is a catadioptric telescope that combines elements from both the Schmidt camera and the Newtonian reflector. In this telescope design a spherical primary mirror is combined with a Schmidt corrector plate, which corrects the spherical aberration. The resulting system has less coma than a reflecting telescope with a parabolic mirror. The design uses a 45° flat secondary mirror to view the image, as in a standard Newtonian 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. James Gregory was a contemporary of Isaac Newton, both often worked simultaneously on similar projects. Gregory's design was published in 1663 and pre-dates the first practical reflecting telescope, the Newtonian telescope, built by Sir Isaac Newton in 1668. However, Gregory's design was only a theoretical description and he never actually constructed the telescope. It was not successfully built until five years after Newton's first reflecting telescope.

Curved mirror type of mirror

A curved mirror is a mirror with a curved reflecting surface. The surface may be either convex or concave. Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are sometimes used in optical devices. The most common non-spherical type are parabolic reflectors, found in optical devices such as reflecting telescopes that need to image distant objects, since spherical mirror systems, like spherical lenses, suffer from spherical aberration. Distorting mirrors are used for entertainment. They have convex and concave regions that produce deliberately distorted images.

The following timeline lists the significant events in the invention and development of the telescope.

Mangin mirror

In optics, a Mangin mirror is a negative meniscus lens with the reflective surface on the rear side of the glass forming a curved mirror that reflects light without spherical aberration. This reflector was invented in 1876 by a French officer Alphonse Mangin as an improved catadioptric reflector for search lights and is also used in other optical devices.

Reflecting instruments are those that use mirrors to enhance their ability to make measurements. In particular, the use of mirrors permits one to observe two objects simultaneously while measuring the angular distance between the objects. While reflecting instruments are used in many professions, they are primarily associated with celestial navigation as the need to solve navigation problems, in particular the problem of the longitude, was the primary motivation in their development.

An Elton's quadrant is a derivative of the Davis quadrant. It adds an index arm and artificial horizon to the instrument. It was invented by John Elton a sea captain who patented his design in 1728 and published details of the instrument in the Philosophical Transactions of the Royal Society in 1732.


The Astroscan was a wide-field 4⅛" clear-inch (105mm) diameter reflecting telescope, originally produced by the Edmund Scientific Corporation, that was for sale from 1976 to 2013.

Aerial telescope very long focal length refracting telescope without a tube, built in the 17th century; the objective was mounted on a pole, tree, etc. on a swivel ball-joint; the observer stood on the ground and maneuvered the eyepiece to aim at celestial objects

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 the eyepiece, which was connected to the objective by a string or connecting rod. By holding the string tight and maneuvering the eyepiece, the observer could aim the telescope at objects in the sky. The idea for this type of telescope may have originated in the late 17th century with the Dutch mathematician, astronomer and physicist Christiaan Huygens and his brother Constantijn Huygens, Jr., though it is not clear if they actually invented it.

Spencer, Browning & Rust

Spencer, Browning & Rust was a London firm that manufactured instruments for navigational use during the 18th and 19th centuries. The predecessor company of Spencer and Browning was established by William Spencer and Samuel Browning in 1778, before they entered into partnership with Ebenezer Rust in 1784. After the death of Ebenezer Rust's son, the successor business was known as Spencer, Browning & Co. The firm of Spencer, Browning & Rust made a variety of navigational instruments, including octants and sextants.


  1. Correspondence between William Penn and James Logan. Philadelphia: J. B. Lippincott & Co. 1870.
  2. "John Hadley" . Retrieved 15 March 2016.
  3. Institute and Museum of the History of Science, Florence, Italy: Picture of Hadley's octant
  4. - Hadley’s Reflector
  5. The complete Amateur Astronomer - John Hadley's Reflector
  6. Henry C. King - The history of the telescope - page 77
  7. telescopeѲ - 8.2. Two-mirror telescopes
  8. Oasis Academy in NE Enfield Archived 22 February 2009 at the Wayback Machine . Retrieved 5 February 2009

Further reading