Ramsden.info - Famous
Ramsdens
Ramsden.info - Famous
Ramsdens
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The Ramsden Chain was constructed by Jesse Ramsden under the specifications and order of the British 'Royal Engineers' General William Roy for the 1784 baseline measure of Hounslow Heath, London, (in prelude to the British Ordnance Survey).
The Ramsden Chain is generally referred to as the Engineer's Chain, as it was used by the Royal Engineers under the auspices of the Royal Society, and it is a longer and more accurately engineered descendant of the wire Gunter Chain (referred to as the Surveyors Chain) as used by surveyors since the 17th Century.
As you can see from the picture below, the Ramsden chain is made of steel bars (for consistency of length—cannot be stretched or as easily worn as the wire type Gunter chain), fitted with double hinged joints (to allow for easy folding and portability), and ended by curved brass handles.
A surviving example of the Ramsden Chain as pictured
from the Science Museum.
Notice how the links are of solid steel bars, and the hinges are double jointed (identical
to those used in bike chains today).
See also how the handles and at every 20th link (20ft) the hinged joint is 90 degrees to
the normal (see the rear left edge of the picture),
allowing for the chain to be folded into a compact group of 5 sections of 20 links.
Each length measured 1 foot (mid hinge to mid hinge), and the 100 link chain in total measured 100 feet (handle to handle). This length was most likely chosen to make the arithmetic easier for long distance surveyors who used trigonometry to calculate the distance and relative position of a distant landmark based upon calculations from measurements made at either end of the outstretched chain used as a base line. Note that all calculations at that time were necessarily made using pencil and paper (as calculators weren't possible), and simplifying calculations to a factor of 100 (as the metric system now does) would have made things easier in the calculations for those of the time. Thus the invention of the 100 foot 'Ramsden Chain'.
Here is a copy of the first survey map (plan drawing)
showing Hounslow Heath south of London,
as surveyed by General William Roy of the Royal Engineers under the auspices of the Royal
Society in 1784.
It also shows the 100ft Ramsden Chain used in the survey.
See the brass tags on the 90 degrees to the normal hinged joints (see the front left edge
of the bundled chain)
used to measure a tenth section of the chain (10ft). These brass tags were likely
stamped to identify their position in the chain.
Prior to the invention of the 100ft Ramsden Chain (Engineer's Chain) used by the British Royal Engineers for their engineering purposes, the shorter (66ft) Surveyor's Chain was used as an indisputable and common (fair to all measured by the chain) standard measure of linear distance to survey an area of land. Usage dates from the 17th century, and is named after the English mathematician Edmund Gunter (1581–1626). (Incidentally, Gunter was the first to accurately measure logarithmic sines and tangents (extended to 7 decimal places) for every degree and minute of the quadrant and publish them in his Canon Triangulorum in 1620. He is also attributed with the naming of the cosine and cotangent of the complement angle in a triangle.)
The traditional surveyor's chain of measure was made from steel or brass wire, and was designed to provide an indisputable measure of distance for property owners and farmers at a time when borders between fields in England (inherited from ancestral boundaries) caused disparate land ownership quarrels, especially with the Crown when being taxed on land area usage.
The 100 link 'Surveyors Chain' (Gunter's) showing marked
brass tags attached every 10 links .
See that they are marked with 1 to 4 teeth incrementing from each handle end.
This would allow for the
accurate measurement to a tenth of the chain.
The chain measured 4 Rods ( 66ft) and was first used to survey (measure for assessment) the area of a ploughed field .
At a fixed length of 66 feet, the (surveyors) chain consisted of a 100 linked wire segments with a looped handle on each end, and was used by property surveyors to quickly and easily measure relatively short distances of land in multiples of chains. They simply laid the chain out across the land in a straight line and extended the chain to its maximum length by having a person on either end hold the chain up and use their body weight to pull the chain taut. When used with stakes, the total distance between ends—stake to stake—was the prescribed length of 1 chain.
If the chain had been folded properly, an experienced chainman (surveyor's assistant) could fling the bundle of chain out to unfold neatly without snagging. Another chainman would grab the far-flung handle, flick to straighten it, pull the chain taut, and then be able to take the measurement. Cleared land would be measured in bays of 1 chain, with the chain being dragged forward for each measured distance. Of course, this method was impractical over uncleared land, like wooded forests. Distance measurements through a forest were only possible when a straight and clear line of sight could be established for the length of the chain line.
The 100 link (66ft) Gunter Surveyor's brass chain
complete with painted steel stakes.
Why one stake is twisted and the other is straight is beyond my current understanding.
Note that the links are soldered, not open.
With so many links in the chain there were many wearing surfaces and after extensive use, the round links also became slightly oval, resulting in chains commonly stretching beyond their designated length. It is also alleged that some surveyors added an extra link so that their surveys always included a greater physical area than the actual measurements indicated (the landowners weren't going to complain!). When retracing old surveys with modern equipment, a modern surveyor will almost always find his measurements are longer than the originals (because his chain is shorter—and more accurate—than his predecessors' chains).
A foot was measured as the actual length of a Roman soldier's foot (around the origin of the Christian era 1AD), and the term has survived into modern English language although the actual physical length has changed over time. The Ancient Roman foot has the modern equivalent of 296mm. It has since been redefined as the actual length of the foot of the reigning King of England in ??? Henry ?.
The yard (3 Roman foot) was the double step length of a Roman soldier in marching formation and the Roman mile was the equivalent of 1000 yards. Therefore a Roman mile is also 3000 Roman feet.
The standard chain measures 4 rods long, 1/10 furlong, 22 yards, or 20.1168 meters. The traditional length of a cricket pitch is 1 chain. Gunter's chain has the useful property that an acre is exactly 10 square chains.
As a unit of measurement within the Imperial system, the chain is defined as 22 yards, 66 feet, or 4 rods. Ten chains made one furlong, and 8 furlongs to a mile means there are 80 chains to a mile. In metric units, a chain equals 20.1168 metres. A chain is divided into 100 links.
American surveyors sometimes used a longer chain of 100 feet, known as the engineer's chain or Ramsden's chain.
The chain is equal to exactly 1/80 mile.
The chain unit was once important in everyday life, being one of the fundamental units of Imperial system in the United Kingdom and its colonies, and was used to some extent in engineering and surveying in the U.S.
In Britain, it was commonly used in the railway industry (where the measure is still in widespread use). Mapping by the Ordinance Survey (Britain's national mapping organisation) began in the early 19th century using the chain as the basic unit of measurement. All map scales at that time were expressed as a relative fraction of a chain or a mile (e.g. a one inch to ten chain scale was equivalent to 1:7920)
The use of the chain was once very common in laying out townships and mapping the US along the train routes in the 19th century. In the U.S. a federal law was passed in 1785 (The Public Land Survey Ordinance) that all official government surveys must be done with a Gunter's chain (also referred to as the 'surveyor's chain').
The chain also survives, in fact if not always in name, in two other specific contexts.
It is the length of the pitch, between the wickets, in cricket. It lies at the origin of the definition of an acre as 4840 square yards. The original acre was an area of land suitable for ploughing in a defined time, and was therefore not square; it measured one chain by one furlong (10 square chains).
In the laying out of towns in Australia and New Zealand, most building lots in the past were a quarter of an acre, measuring 1 chain by 2 and a half chains, and other lots would be multiples or fractions of a chain. As a consequence, the street frontages of many houses in these countries are one chain wide — roads were almost always one chain wide (20.117m) in urban areas, sometimes one and a half (30.175m) or 2 chains (40.234m). Laneways would be half a chain (10.058m). In rural areas the roads were wider, up to 10 chains (201.17m) where a stock route was required.
According to http://www.everestmountain.com/hommages_p1.htm The highest mountain in the world was named after the Surveyor -General of India, Colonel Sir George Everest. When Everest "inherited" the position in 1823, the equipment originally employed by Lambton consisted of one 36" theodolite manufactured by London instrument maker Cary, a zenith sector by Jesse Ramsden, a Ramsden 100 foot steel chain, and a chronometer. The Cary theodolite, weighing over one thousand pounds, had been damaged in two separate mishaps, and was badly in need of repair. The micrometer screw on the zenith sector was worn out, and the steel chain had not been calibrated in twenty-five years. Thus it appears, that the Ramsden Chain is also likely an invention by Jesse Ramsden, as its timeframe places its manufacture into the previous century, at a time when his measuring equipment was state of the art and in known use of the British Government.
According to http://www.h-net.org/~rural/threads/disceasmeasure.html the Ramsden chain is 'for sesquipedalian surveyors', (sesquipedalian: a foot and a half, or extra long) which I think provides a purpose for this longer chain. As we know the Gunter's Chain (66ft) was used for surveying plots of land, towns and roads, and is referred to as the surveyors chain, then the purpose of an engineering chain (100ft) was to survey longer distances, so having one in a metric size made mathematics much simpler for the surveyor (and more likely to be accurate) for the Ramsden Chain.
According to http://www.scienceandsociety.co.uk/results.asp?image=10280167&wwwflag=2&imagepos=6 The 100 link steel surveying chain, 1784 (pictured) was made by Jesse Ramsden, and used in the Primary Triangulation of Great Britain. This was a network of measured triangles across the country, used to underpin maps. The network was checked in a number of places by setting up a base line, several miles long, and comparing measured and calculated dimensions. The first line was on Hounslow Heath and General William Roy of the Royal Engineers used this chain for its measurement.
And now we're getting down to some accurate details. According to http://www.makingthemodernworld.org.uk/stories/enlightenment_and_measurement/05.ST.05/?scene=4 Surveying was an important activity in the eighteenth century for several reasons. The enclosure of common land was proceeding rapidly, the military needed better maps for successful campaigns and finding longitude accurately required tables which depended on the relative position of the Greenwich and Paris observatories. Long-standing debates such as the shape of the Earth were tackled by the first large-scale international expeditions. The end of the century witnessed the beginning of the first ordnance survey of Great Britain.
Although there had been several maps of the colonies, it was not until 1783 (when peace was eventually declared with France) that Cassini de Thury of the Paris Observatory proposed the triangulation of the Southeast of England. This was in order to link with the French triangulation so that the exact relative position of the two observatories could be established. William Roy, who was placed in charge of the project, suggested that it was necessary to 'reinvent them all'. He commissioned Jesse Ramsden, the leading instrument maker of the time, to construct a 3' theodolite weighing 200lb.
While there was no innovation in the principle of the instrument, this theodolite was bigger and better than anything preceding it. Users were able to read a mark at 70 feet with an error of only two seconds. It was called ‘the father of accurate surveying instruments’. The same could be said of Ramsden's 100 foot chain, also commissioned and used on the project.
The British Library 'Collect Britain' Ordnance Survey Drawings (http://www.collectbritain.co.uk/collections/osd/textintro.cfm) topic provides a very interesting introduction to the Great British Ordnance Survey from 1795 to 1874, and has possession of 351 of the original detailed preliminary drawings made by the surveyors up to 1840, detailing everything south of a line drawn roughly between Liverpool and Hull.
Being significantly larger in scale, the preliminary drawings show much more detail than the printed maps. Together, they present a picture of Regency England and Wales unparalleled in its accuracy. Critical communication routes such as roads and rivers were to be shown clearly and accurately.
A theodolite was used to measure the angles of a remote point from each end of a steel chain. The triangle formed by the known length of the chain and the two sight lines enabled the precise distance of the far point to be calculated by trigonometry. The theodolite, specially built by Jesse Ramsden, was a formidable instrument, almost a metre in diameter and weighing over ninety kilos. A four-wheeled sprung carriage pulled by two horses was needed to move it from place to place.
According to http://home.bt-webworld.com/tides/ebbd.htm, at the beginning of the present century the system of triangulation carried on in 1784 and 1787 by General Roy, under the auspices of the Royal Society, for the geodetic connection of Greenwich and Paris observatories, and resumed after Roy's death by the board of ordnance for a survey of South Britain, had extended over the southern counties into Devonshire and Cornwall. It was becoming the custom to attach young engineer officers to the survey for a time to learn topographical drawing under the ordnance draughtsmen. Either in this way or through the good offices of his uncle, Colonel Hadden, royal artillery, at that time secretary to the master-general, young Colby attracted the notice of Major Mudge, director of the ordnance survey, who asked that he should be attached in some permanent manner to that duty. The request was granted the same day, 12 Jan. 1802, on which date commenced the future General Colby's connection with the ordnance survey, which ultimately extended over a period of forty-five years. Up to that date the British ordnance survey had helped little towards the solution of the great astronomical problem of the earth's figure, but the tardy completion of a new zenith-sector, a noble instrument, ordered by the board of ordnance from the famous maker, Ramsden, years before, induced Major Mudge to apply the projected extension northwards of the ordnance triangulation to the measurement of an arc of the meridian between Dunnose, Isle of Wight, and a station near the mouth of the Tees, and the young lieutenant's first services appear to have been in connection with the sector observations made at Dunnose in the summer of 1802.
See Jesse Ramsden.
http://www.answers.com/topic/chain-unit duplicated at http://www.nationmaster.com/encyclopedia/Chain-(length)
http://www.measuringamerica.com/gallery.php
An interesting story of surveying in the USA around 1800 is described at http://www.profsurv.com/ps_scripts/article.idc?id=301