The Ramsden theodolite is a large 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...

 that was specially constructed for use in the first Ordnance Survey

Ordnance Survey

Ordnance Survey , an executive agency and non-ministerial government department of the Government of the United Kingdom, is the national mapping agency for Great Britain, producing maps of Great Britain , and one of the world's largest producers of maps.The name reflects its creation together with...

 of Southern Britain

Kingdom of Great Britain

The former Kingdom of Great Britain, sometimes described as the 'United Kingdom of Great Britain', That the Two Kingdoms of Scotland and England, shall upon the 1st May next ensuing the date hereof, and forever after, be United into One Kingdom by the Name of GREAT BRITAIN. was a sovereign...

. It was also known as the Great or 36 inch theodolite.

The theodolite was commissioned from Jesse Ramsden

Jesse Ramsden

Jesse Ramsden FRSE was an English astronomical and scientific instrument maker.Ramsden was born at Salterhebble, Halifax, West Riding of Yorkshire, England. After serving his apprenticeship with a cloth-worker in Halifax, he went in 1755 to London, where in 1758 he was apprenticed to a...

, a leading Yorkshire

Yorkshire

Yorkshire is a historic county of northern England and the largest in the United Kingdom. Because of its great size in comparison to other English counties, functions have been increasingly undertaken over time by its subdivisions, which have also been subject to periodic reform...

 instrument maker, who had developed an accurate dividing engine

Dividing engine

A dividing engine is a device specifically employed to mark graduations on measuring instruments.-History:There has always been a need for accurate measuring instruments...

 for graduating

Graduation (instrument)

-Linear graduation:Linear graduation of a scale occurs on a straight instrument. The graduation can identify linear measures, such as inches or millimetres on a rule. They can also be non-linear such as logarithmic or other transcendental scales....

 angular scales

Angle

In geometry, an angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle.Angles are usually presumed to be in a Euclidean plane with the circle taken for standard with regard to direction. In fact, an angle is frequently viewed as a measure of an circular arc...

. The instrument was accurate to within a second of arc. The theodolite took three years to build and had a base circle of 3 ft (914 mm).

The full survey

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...

, sometimes called the Principal Triangulation of Great Britain

Principal Triangulation of Great Britain

The Principal Triangulation of Britain was a triangulation project carried out between 1783 and about 1853 at the instigation of the Director of the Ordnance Survey General William Roy ....

, was begun in 1791 by a team formed under General William Roy

William Roy

Major-General William Roy FRS was a Scottish military engineer, surveyor, and antiquarian. He was an innovator who applied new scientific discoveries and newly emerging technologies to the accurate geodetic mapping of Great Britain....

 (d 1790).. The survey used the new theodolite on a specially surveyed baseline

Baseline (surveying)

In the United States Public Land Survey System, a baseline is the principal east-west line that divides survey townships between north and south. The baseline meets its corresponding meridian at the point of origin, or initial point, for the land survey...

 based on Roy's accurate surveys between 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...

 and Paris

Paris

Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...

.

Traces of the theodolite support structure were still to be found many years afterwards at some remote survey points, such as at Soldiers' Lump, the summit of Black Hill

Black Hill (Peak District)

Black Hill is a hill in the Peak District, England.It used to be the highest point in Cheshire, but now lies on the border between the boroughs of Kirklees in West Yorkshire and High Peak in Derbyshire, reaching above sea level....

 in the Peak District

Peak District

The Peak District is an upland area in central and northern England, lying mainly in northern Derbyshire, but also covering parts of Cheshire, Greater Manchester, Staffordshire, and South and West Yorkshire....

 of England.

The theodolite is now in the Science Museum

Science Museum (London)

The Science Museum is one of the three major museums on Exhibition Road, South Kensington, London in the Royal Borough of Kensington and Chelsea. It is part of the National Museum of Science and Industry. The museum is a major London tourist attraction....

 in London.

Ramsden, who was elected to the Royal Society

Royal Society

The Royal Society of London for Improving Natural Knowledge, known simply as the Royal Society, is a learned society for science, and is possibly the oldest such society in existence. Founded in November 1660, it was granted a Royal Charter by King Charles II as the "Royal Society of London"...

 in 1786, and was awarded the Copley Medal

Copley Medal

The Copley Medal is an award given by the Royal Society of London for "outstanding achievements in research in any branch of science, and alternates between the physical sciences and the biological sciences"...

 in 1795 for his instruments, also made important contributions to fields such as optics

Optics

Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...

 (the Ramsden eyepiece) and electrostatics

Electrostatics

Electrostatics is the branch of physics that deals with the phenomena and properties of stationary or slow-moving electric charges....

(the Ramsden machine).