Gunter's chain
Encyclopedia
Gunter's chain is a measuring device used for land survey. It was designed and introduced in 1620 by English clergyman and mathematician Edmund Gunter
(1581–1626) long before the development of the theodolite
and other more sophisticated equipment, enabling plots of land to be accurately surveyed and plotted, for legal and commercial purposes.
A 1675 description states of the Gunter's Chain, "Dimensurator or Measuring Instrument whereof the mosts usual has been the Chain, and the common length for English Measures 4 Poles, as answering indifferently to the Englishs Mile and Acre, 10 such Chains in length making a Furlong, and 10 single square Chains an Acre, so that a square Mile contains 640 square Acres." ---John Ogilby, Britannia, 1675
Today in Britain, the Gunter Chain's most famous legacy is that it gave us the accurate length of the cricket pitch
.
Gunter divided the chain into 100 links, marked off into groups of 10 by brass rings which simplified intermediate measurement. On the face of it, the dimensions make no sense: Each link is 7.92 inches long; 10 links make slightly less than 6 feet 8 inches and a full length of 66 feet. In fact, he had made a brilliant synthesis of two
incompatible systems, the traditional English land measurements, based on the number 4, and the newly introduced system of decimals based on the number 10.
"Gunter's chain allowed either method to be used. An acre
measured 4,840 square yards in traditional units and 10 square
chains in Gunter's system. Thus, if need be, the entire process of land measurement could be computed in decimalized chains
and links, and then converted to acres by dividing the results by 10."
Illustrations are available online.
Richard Norwood
used one in his 1633–1635 traverse of London to York
(see his book A Sea-Man’s Practice).
The method of surveying
a field or other parcel of land was to determine corners and other significant locations, and then to measure the distance between them, taking two points at a time. The surveyor is assisted by a chainman. A ranging rod (usually a prominently coloured wooden pole) is placed in the ground at the destination point. Starting at the originating point the chain is laid out towards the ranging rod, and the surveyor then directs the chainman to make the chain perfectly straight and pointing directly at the ranging rod. A pin is put in the ground at the forward end of the chain, and the chain is moved forward so that its hind end is at that point, and the chain is extended again towards the destination point. This process is called ranging
, or in the US, chaining; it is repeated until the destination rod is reached, when the surveyor notes how many full lengths (chains) have been laid, and he can then directly read how many links (one-hundredth parts of the chain) are in the distance being measured.
The whole process is repeated for all the other pairs of points required, and it is a simple matter to make a scale diagram of the plot of land. The process is surprisingly accurate and requires only very low technology. Surveying with a chain is simple if the land is level and continuous—it is not physically practicable to range across large depressions or significant waterways, for example. The triangulation method requires that the land is plane (not varying significantly in slope). On sloping land, the chain was to be "leveled" by raising one end as needed, so that undulations did not increase the apparent length of the side or the area of the tract.
The theodolite
, developed later, enables accurate assessment of angles, and surveying points over long distances became possible. The Gunter's chain was still in use for small surveys in the second half of the twentieth century. In the US, Public Lands Survey plats are still published in the Chain unit to maintain the consistency of a two-hundred-year-old database.
The chain
as a unit of length of 66 feet (20.1168 m) and the link, one-hundredth of a chain, probably developed as a result of the introduction of Gunter's chain as the technique of surveying; but it is important not to confuse the two; Gunter's chain is the physical device used in the field. A chain also has the commonly used subunit variously called a "rod", a "pole" or a "perch", which was 16.5 feet long, or one fourth of a chain (5.0292 m).
Edmund Gunter
Edmund Gunter , English mathematician, of Welsh descent, was born in Hertfordshire in 1581.He was educated at Westminster School, and in 1599 was elected a student of Christ Church, Oxford. He took orders, became a preacher in 1614, and in 1615 proceeded to the degree of bachelor in divinity...
(1581–1626) long before the development of the theodolite
Theodolite
A theodolite is a precision instrument for measuring angles in the horizontal and vertical planes. Theodolites are mainly used for surveying applications, and have been adapted for specialized purposes in fields like metrology and rocket launch technology...
and other more sophisticated equipment, enabling plots of land to be accurately surveyed and plotted, for legal and commercial purposes.
A 1675 description states of the Gunter's Chain, "Dimensurator or Measuring Instrument whereof the mosts usual has been the Chain, and the common length for English Measures 4 Poles, as answering indifferently to the Englishs Mile and Acre, 10 such Chains in length making a Furlong, and 10 single square Chains an Acre, so that a square Mile contains 640 square Acres." ---John Ogilby, Britannia, 1675
Today in Britain, the Gunter Chain's most famous legacy is that it gave us the accurate length of the cricket pitch
Cricket pitch
In the game of cricket, the cricket pitch consists of the central strip of the cricket field between the wickets - 1 chain or 22 yards long and 10 feet wide. The surface is very flat and normally covered with extremely short grass though this grass is soon removed by wear at the ends of the...
.
Gunter divided the chain into 100 links, marked off into groups of 10 by brass rings which simplified intermediate measurement. On the face of it, the dimensions make no sense: Each link is 7.92 inches long; 10 links make slightly less than 6 feet 8 inches and a full length of 66 feet. In fact, he had made a brilliant synthesis of two
incompatible systems, the traditional English land measurements, based on the number 4, and the newly introduced system of decimals based on the number 10.
"Gunter's chain allowed either method to be used. An acre
Acre
The acre is a unit of area in a number of different systems, including the imperial and U.S. customary systems. The most commonly used acres today are the international acre and, in the United States, the survey acre. The most common use of the acre is to measure tracts of land.The acre is related...
measured 4,840 square yards in traditional units and 10 square
chains in Gunter's system. Thus, if need be, the entire process of land measurement could be computed in decimalized chains
and links, and then converted to acres by dividing the results by 10."
Illustrations are available online.
Richard Norwood
Richard Norwood
Richard Norwood was an English mathematician, diver, and surveyor, connected with Isaac Newton. He has also been called "Bermuda’s outstanding genius of the seventeenth century"...
used one in his 1633–1635 traverse of London to York
York
York is a walled city, situated at the confluence of the Rivers Ouse and Foss in North Yorkshire, England. The city has a rich heritage and has provided the backdrop to major political events throughout much of its two millennia of existence...
(see his book A Sea-Man’s Practice).
The method of surveying
Surveying
See Also: Public Land Survey SystemSurveying or land surveying is the technique, profession, and science of accurately determining the terrestrial or three-dimensional position of points and the distances and angles between them...
a field or other parcel of land was to determine corners and other significant locations, and then to measure the distance between them, taking two points at a time. The surveyor is assisted by a chainman. A ranging rod (usually a prominently coloured wooden pole) is placed in the ground at the destination point. Starting at the originating point the chain is laid out towards the ranging rod, and the surveyor then directs the chainman to make the chain perfectly straight and pointing directly at the ranging rod. A pin is put in the ground at the forward end of the chain, and the chain is moved forward so that its hind end is at that point, and the chain is extended again towards the destination point. This process is called ranging
Ranging
Ranging is a process or method to determine the distance from one location or position to another location or position. Another term for this method is lateration, see unilateration...
, or in the US, chaining; it is repeated until the destination rod is reached, when the surveyor notes how many full lengths (chains) have been laid, and he can then directly read how many links (one-hundredth parts of the chain) are in the distance being measured.
The whole process is repeated for all the other pairs of points required, and it is a simple matter to make a scale diagram of the plot of land. The process is surprisingly accurate and requires only very low technology. Surveying with a chain is simple if the land is level and continuous—it is not physically practicable to range across large depressions or significant waterways, for example. The triangulation method requires that the land is plane (not varying significantly in slope). On sloping land, the chain was to be "leveled" by raising one end as needed, so that undulations did not increase the apparent length of the side or the area of the tract.
The theodolite
Theodolite
A theodolite is a precision instrument for measuring angles in the horizontal and vertical planes. Theodolites are mainly used for surveying applications, and have been adapted for specialized purposes in fields like metrology and rocket launch technology...
, developed later, enables accurate assessment of angles, and surveying points over long distances became possible. The Gunter's chain was still in use for small surveys in the second half of the twentieth century. In the US, Public Lands Survey plats are still published in the Chain unit to maintain the consistency of a two-hundred-year-old database.
The chain
Chain (unit)
A chain is a unit of length; it measures 66 feet or 22 yards or 100 links . There are 10 chains in a furlong, and 80 chains in one statute mile. An acre is the area of 10 square chains...
as a unit of length of 66 feet (20.1168 m) and the link, one-hundredth of a chain, probably developed as a result of the introduction of Gunter's chain as the technique of surveying; but it is important not to confuse the two; Gunter's chain is the physical device used in the field. A chain also has the commonly used subunit variously called a "rod", a "pole" or a "perch", which was 16.5 feet long, or one fourth of a chain (5.0292 m).