Accession No
2471
Brief Description
6-inch transit theodolite by Troughton and Simms, c.1880
Origin
London; England
Maker
Troughton & Simms
Class
surveying
Earliest Date
1880
Latest Date
1880
Inscription Date
Material
metal (brass, other); glass; wood
Dimensions
box length 400mm; breadth 345mm; height 215mm; horizontal circle diameter 168mm; height 360mm; telescope length 288mm
Special Collection
Provenance
Transferred from Department of Engineering, University of Cambridge, Cambridge, England, 09/1979.
Inscription
‘Troughton and Simms LONDON’ (on compass face)
Description Notes
Metal alloy construction with brass screws. Telescope with rack and pinion focus moving the objective. Inverting, sliding eyepiece. Ray shade; cross hairs. Telescope transits over the eyepiece. Bubble mounted over the telescope; graduated to 1/10˝. 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 (inside frame). Clipping screws. ‘A’ frame with one bubble mounted outside the frame and the second perpendicular on the horizontal circle. Central compass with 8-point silvered rose; 2 scales one divided 0 - 90 - 0 - 90 - 0˚ and other 0 - 360˚ subdivided to 1; lever opertaed locking bar. Horizontal circle with silvered scale divided 0 - 360˚ subdivided to 20´ of arc and read by 2 verniers to 20˝ of arc. Clamp and motion screws for vernier plate and horizontal circle. 3 levelling feet on tribrach limbs. 2 microscopes slot onto horizontal circle to read vernier scales. Trivet base with clamp for levelling feet and thread for attachment to tripod. Erecting lens. 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:42905
Images (Click to view full size):
