Accession No
2466
Brief Description
4-inch transit theodolite by Troughton and Simms, English, 1905 (c)
Origin
England; London
Maker
Troughton and Simms
Class
surveying
Earliest Date
1905
Latest Date
1905
Inscription Date
Material
metal (brass, aluminium, other); glass; wood
Dimensions
box length 340mm; breadth 300mm; height 174mm; horizontal circle diameter 119mm; telescope length 238mml height 300mm
Special Collection
Provenance
Transferred from Department of Engineering, University of Cambridge, Cambridge, England, 09/1979.
Inscription
‘TROUGHTON & SIMMS LONDON’ (on horizontal circle)
Description Notes
Metal alloy construction with black finish and brass screws. Telescope with rack and pinion focus moving the objective. Inverting, sliding eyepiece. Ray shade; cross hairs. Vertical circle with silvered scale divided 0 - 90 - 0˚, subdivided to 20’ of arc; read by 2 opposing veniers and microscopes to 20´´ of arc. Clamp and motion screws for vertical circle. Clipping screws. ‘A’ frame with both bubbles mounted on horizontal circle. Horizontal circle with silvered scale divided 0 - 360˚ and read by verniers and hinged microscopes to 20˜ of arc. Clamp and motion screws for vernier plate operated by spring-bar on horizontal circle. Clamp and motion for horizontal circle. 3 levelling feet on tribrach limbs. Trough compass with silvered scale divided 5 - 0 - 5˚ slots under horizontal circle. Erecting lens. Plumb-bob. Spare cross hairs in aluminium case. Trivet base with clamp for levelling feet and thread for attachment to tripod. Fitted wooden box.
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:42906
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