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Jesse Ramsden, the greatest instrument maker of the late eighteenth century, is now known to have constructed three theodolites, great in name, great in size and great in accuracy. Two further instruments were completed by Mathew Berge, his son-in-law, and business successor, shortly after Ramsden's death in 1805. (Insley 2008). The first two of these instruments were used for high precision geodetic measurements in Great Britain from 1787 to 1862. Ramsden also provided the equipment used in the measurement of the many base lines of these surveys.
The great theodolites
Ramsden RS, the first theodolite
Ramsden BO, the second theodolite
The third theodolite
The two Berge theodolites
Three other great theodolites
Chains and Rods
The theodolite was commissioned from Jesse Ramsden, a leading Yorkshire instrument maker, who had developed an accurate dividing engine for graduating angular scales. 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, sometimes called the Principal Triangulation of Great Britain, was begun in 1791 by a team formed under General William Roy (d 1790). The survey used the new theodolite on a specially surveyed baseline based on Roy's accurate surveys between London and Paris.
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 in the Peak District of England.
Ramsden, who was elected to the Royal Society in 1786, and was awarded the Copley Medal in 1795 for his instruments, also made important contributions to fields such as optics (the Ramsden eyepiece) and electrostatics (the Ramsden machine).
- Insley, Jane (2008), The Tale of the Great Theodolites, FIG Working Week
- Seymour, W.A., ed. (1980), A History of the Ordnance Survey, Folkestone: Wm Dawson & Sons, p. 21
- Wainwright, A. Pennine Way Companion ISBN 0-7112-2235-5 p.157
- Ramsden's three foot geodetic theodolite, 1792, Science Museum, retrieved 2010-07-10
- Library and Archive catalogue, Royal Society, retrieved 2011-07-10
- Copley archive winners, 1799-1731, Royal Society, retrieved 2011-07-11