Accession No

2116

Brief Description

6-inch transit theodolite, by Troughton and Simms, English, c.1840

Origin

England; London

Maker

Troughton and Simms

Class

surveying

Earliest Date

1840

Latest Date

1840

Inscription Date

Material

metal (brass, 1 other); glass

Dimensions

telescope length 294mm; horizontal circle diameter 165mm; height (excluding striding level) 369mm; box length 410mm; breadth 395mm; height 234mm

Special Collection

Provenance

On loan from Royal Astronomical Society, London from 02/11/1984 Belonged to Rev R. Sheepshanks. Presented by Miss Anne Sheepshanks (his sister) to the Royal Astronomical Society in 1857.

Inscription

‘Troughton and Simms, LONDON’ (on circles)
‘Royal Astronomical Society
Presented by Miss
Sheepshanks, No2 ‘ (on telescope)
‘RAS NO.2.’ (on all parts)

Description Notes

Metal alloy with brass screws. Telescope with rack and pinion focus moving the objective; cross hairs; lens cover. Bubble mounted outside vertical circle. Clamp and motion screws at top of circle. Silvered scale graduated 0 - 90 - 0; read by verniers and microscopes to 10’ (?). ‘A’ frame. Clipping screws inside frame. Bubble mounted on horizontal circle. Silvered scale graduated 0 - 360˚ to 10’ of arc. Read by vernier and microscopes to 10’ of arc. Clamp and motion screws for vernier plate and horizontal circle. 3 levelling feet on tribrach limbs. Fitted wooden box. Striding level; plumb-bob. Trough compass graduated 9˚ - 0 - 9˚. Lamp for artificial illumination. Spare bubble level; dark glass; diagonal lens; 3 spare eyepieces; and assorted spare parts

Condition good.

This object is on loan from the Royal Astronomical Society.

References

Events

Description
The theodolite is a relatively simple tool used for measuring angles, both horizontal and vertical. They work using the same principles as a protractor: the ‘point A’ is located and the angle noted, and then the telescope is pointed at ‘point B’ and the second angle is taken.

Although primarily used in surveying the theodolite can be applied to both Meteorology and Navigation.

Gemma Frisius proposed the idea behind the theodolite in 1533. At the time new methods of surveying were being used and by combining an Alidade, a magnetic compass and the degree scale on the back of an Astrolabe, the calculations made by modern theodolites could be observed. Unfortunately, this method was not practical due to the combination of instruments. The best of the attempts to simplify the process was the ‘theodolitus’, first described in print by Leonard Digges in 1571.

However, this instrument could only take measurements in the horizontal plane. Despite this it was still thought of as the ‘common’ Theodolite up to the late 18th century.

During the 19th century the Altazimuth Theodolite was considered the most useful theodolite, as it could measure on the horizontal and vertical planes. Three notable types of Altazimuth Theodolite were developed: The Everest Theodolite, the Plain Theodolite and the Transit Theodolite. It is the Transit Theodolite, which is still used today.

FM:43356