Accession No
2473
Brief Description
transit theodolite, by Cooke, Troughton and Simms, English, 1942
Origin
England; York
Maker
Cooke, Troughton and Simms
Class
surveying
Earliest Date
1942
Latest Date
1942
Inscription Date
Material
metal; glass; cloth (canvas)
Dimensions
case length 380mm; breadth 250mm; height 175mm; horizontal circle diameter 110mm; telescope length 201mm; height 275mm
Special Collection
Provenance
Transferred from Department of Engineering, University of Cambridge, Cambridge, England, 09/1979.
Inscription
‘TAVISTOCK
COOKE TROUGHTON & SIMMS Ltd
YORK ENGLAND
No 41012 Pat. No. 288416’ (on horizontal circle)
Description Notes
Metal alloy construction with grey finish. Inverting telescope with internal focussing by milled ring on end of axis. Eyepiece focus with locking ring. Two eyepiece filters, one engraved ‘L’ the other ‘D’. Cross hairs (3 horizontal). Telescope transits at both ends and has sights. Bubble mounted on transit axis and read by a reversible prism; levelled by a screw at the base of the frame. Horizontal and vertical circles both completely enclosed and read by 2 microscopes pivotted on the frame (they clip into vertical position for fitting into box). Both have green filters, a screw focus and read to 1˝ of arc. Illuminated by mirrors, on axis for vertical circle and on limb for horizontal. Clamp, motion and fine motion screws for vertical and horizontal circles. Bubble mounted on the horizontal circle. 3 levelling feet on tribrach limbs clamped onto base plate. Point on tribrach for artificial illumination of circles by batteries strapped to tripod. Lens cover; ray shade. Fitted metal box with canvas strap; contains 2 leather cases with accessories, including plumb-bob, 5 lenses, screwdriver, brushes etc.
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:42902
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