Accession No

2165

Brief Description

6-inch plain theodolite by Troughton and Simms, c.1900

Origin

London; England

Maker

Troughton & Simms

Class

surveying

Earliest Date

1900

Latest Date

1900

Inscription Date

Material

metal; glass

Dimensions

length 355mm; height 315mm; breadth 190mm

Special Collection

Provenance

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

Inscription

‘TROUGHTON AND SIMMS LONDON’ (on horizontal circle)
‘H.O. ·. 40.’ (on telescope)

Description Notes

Metal alloy. Telescope with rack and pinion focus moving the objective. Inverting, sliding eyepiece. Ray shade. Bubble mounted on telescope graduated. ‘Y supports with clip and pin fastening. Vertical pierced sim-circle graduated in ‘Diff. of hypo and base’ 30 - 0 - 30 on one side and 90 - 0 - 60˚ on the other. Read by vernier to 1’ of arc. Magnifying glass pivots around axis to facilitate reading the vertical scale. Vertical motion controlled by milled screw operating pinion on to rack on outer edge of pierced quadrant [?] mounted below the axis, parallel to the vertical scale. 2 mutually perpendicular bubble levels mounted on horizontal circle. Horizontal scale partially enclosed; silvered and divided 0 - 360˚, subdivided to 20’ of arc and read by 2 opposing verniers and hinged microscopes to 20” of arc. Clamp and motion screw for vernier plate with spring. Clamp and motion screw for horizontal circle. 4 levelling feet between parallel plates. Trough compass slots underneath horizontal circle; silvered scale divided 5˚ - 0 - 5˚; locking bar

Condition

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:42914