Accession No
2159
Brief Description
5-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 (brass, 1 other); glass
Dimensions
height 300mm; length 365mm; breadth 180mm
Special Collection
Provenance
Transferred from Department of Geography, University of Cambridge, Cambridge, England, 05/1969.
Inscription
‘ TROUGTHON & SIMMS LONDON’ (on horizontal circle)
‘H.O. · 82’ (on telescope)
Description Notes
Black painted metal alloy plain theodolite with brass screws.
Inverting telescope with rack and pinion focus moving the objective. Sliding eyepiece. Bubble mounted on telescope graduated in 1/10”.
Telescope attached to ‘Y’ supports over vertical semi-circle by clip and pin fastenings. Silvered scale divided 95 - 0 - 65˚, subdivided to 20’ of arc. Circle rotates with telescope - vernier fixed to horizontal plate. Rear of vertical semi-circle marked ‘Diff of hypo nd Base’ and divided 30 - 0 - 30. Operated by pinion screw on rack on second semi-circle parallel to the vertical semi-circle. 2 bubbles mounted at right angles on the horizontal circle. Horizontal silvered scale divided 0 - 360˚ subdivided to 26’ of arc. Read by two opposing verniers and hinged microscopes to 20” of arc. Clamp and motion screws for vernier plate operated by spring bar. Clamp and motion screw for horizontal circle. 4 levelling feet between parallel plates. Trough compass slots below horizontal circle. Silvered scale divided 5˚ - 0 - 5˚. Lens cover and ray shade. 4 dark glass covers for eyepiece revolve in frame which screws to eyepiece
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:43318
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