Ramsden surveying instruments

Ramsden also provided the equipment used in the measurement of the many base lines of these surveys and also the zenith telescope used in latitude determinations.

Approval having been granted, General William Roy agreed to undertake the work and he immediately approached Ramsden to commission new instruments.

Three years later the "great" theodolite was delivered after a delay attributable to Ramsden's tardiness, workshop accidents and his predilection for continuous refinement—"this won't do, we must have at it again".

It travelled around Britain for over sixty years, in its own sprung carriage, to locations where it was hauled up mountains, church towers and even scaffolded steeples.

The instrument is also fitted with a vertical semi-circular scale to measure the elevations of distant stations and therefore a height difference.

Cross wires similar to those used in the microscopes are fitted into the eyepiece; they are adjustable by a screw thread which allowed angles to be measured to within five arc seconds.

After completion of the Anglo-French Survey this instrument was stored at the Royal Society, but in 1799 the Board of Ordnance requested its use for the Principal Triangulation of Great Britain.

To his delight the East India Company were willing to undertake such a venture and ordered a second great theodolite from Ramsden.

It was bought by the Duke of Richmond who, as Master of the Board of Ordnance, had provided most of the finance for Roy's Anglo-French Survey (1784–1790).

[10] Although the East India Company turned down Ramsden's second theodolite, they commissioned a similar design from another London instrument maker, William Cary.

This last instrument was a monster weighing 1,455 lb (660 kg) when in its travelling cases: it was no surprise that it was deemed too heavy for transport up mountains and it passed to South Africa in 1882.

[15] The zenith telescope constructed by Jesse Ramsden in 1802 was used to determine the latitude of many stations of the Principal Triangulation of Great Britain.