Accession No

2221

Brief Description

5-inch transit theodolite, by Troughton and Simms, English, pre 1922

Origin

England; London

Maker

Troughton and Simms

Class

surveying

Earliest Date

1900

Latest Date

1922

Inscription Date

Material

metal (brass, other); glass; wood

Dimensions

box 1 length 327mm; breadth 405mm; height 204mm box 2 length 395mm; breadth 210mm; height 225mm horizontal circle diameter 145mm; height (without additional bubble) 378mm; height (including additional bubble) 420mm; telescope length 333mm

Special Collection

Provenance

Transferred from Department of Geography, University of Cambridge, Cambridge, England, 05/1969.

Inscription

‘[TROUGHTON AND SIMMS] Ltd LONDON no 20270’ (on horizontal circle)
‘Admiralty HO·160’ (on box)
‘Adjusted 9.3.1933’ (label inside box)

Description Notes

Black finished metal alloy with brass screws.
Telescope with rack and pinion focus moving the objective. Cross hairs. Sights on both sides of telescope which transits over the eyepiece. Vertical circle with silvered scale read by micrometer microscopes to 10” of arc and further by estimation. Bubble mounted on the axis of the micrometer brackets. Clamp and motion screws for vertical circle. Clipping screws. Hollow axis for illumination of telescope.
‘A’ frame with 2 bubbles mounted on horizontal circle which is almost completely enclosed and read by 2 micrometer microscopes to 10” of arc. Clamp and motion screws for plate and horizontal circle. 3 levelling feet on tribrach limbs.
Trivet plate with clamp and central threade hole for attachment to tripod. Lens cover and ray shade. Plumb-bob. Lantern with electrical cables for illumintaing telescope axis. Striding level. Diagonal lens. Erecting diagonal lens. Eyepiece. 2 dark glasses. 2 fitted wooden boxes.

Incomplete

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:43316