Accession No
2168
Brief Description
transit theodolite, by T. Cooke and Sons Ltd., English, 1920 (c)
Origin
England; London and York; and South Africa; Cape Town
Maker
T. Cooke and Sons Ltd.
Class
surveying
Earliest Date
1920
Latest Date
1920
Inscription Date
Material
metal (brass, 1 other); glass; wood
Dimensions
box length 340mm; breadth 225mm; height 340mm horizontal circle diameter 153mm; telescope length 284mm; height 310mm
Special Collection
Provenance
Transferred from Department of Geography, University of Cambridge, Cambridge, England, 05/1969.
Inscription
‘T. COOKE & SONS Ltd
LONDON, YORK, CAPETOWN
No 15624’ (on horizontal circle)
Description Notes
Telescope with rack and pinion focus moving the objective. Inverting, sliding eyepiece; cross hairs. Bubble mounted on telescope and second bubble mounted outside vertical circle. Vertical circle with silvered scale divided 0 - 90˚ - 0 twice. Read by opposing veniers and microscopes to 20” of arc. Clamp and motion screws. Clipping screws.
‘A’ frame. 2 mutually perpendicualr bubble levels mounted on frame. Partially enclosed horizontal circle with silvered scale divided 0 - 360˚ subdivided to 20’ of arc and read by verniers and hinged microscopes to 20” of arc. Clamp and motion screws for horizontal circle and vernier plate. Horizontal circle clamp operates on lowerplate parallel to the principal circle. 3 levelling feet on tribrach limbs.
Trough compass slots onto lower horizontal plate; silvered scale divided 5˚ - 0 - 5˚. Ray shade; plumb-bob; dark glass. Fitted wooden box
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:43315
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