Accession No
2458
Brief Description
4-inch transit theodolite by W. Ottway and Company, 1917
Origin
Maker
Ottway
Class
surveying
Earliest Date
1917
Latest Date
1917
Inscription Date
1917
Material
metal (brass, 1 other); glass; wood
Dimensions
box length 450mm; breadth 172mm; height 173mm; horizontal circle diameter 111mm; telescope length 220mm; height 305mm
Special Collection
Provenance
Transferred from Department of Engineering, University of Cambridge, Cambridge, England, 09/1979.
Inscription
‘W Ottway and Co Ltd. Orion Works Ealing
No 11071 1917’ (on compass face)
Description Notes
Metal alloy with black fininsh and brass screws. Telescope with rack and pinion focus moving the objective. Cross hairs. Principal bubble tube to the left of vertical circle graduated in 1/12”. Vertical circle with scale subdivided to 30’, with vernier scales and 2 microscopes. Clamp and motion screws for vertical circle. ‘A’ frame with one bubble mounted on the horizontal circle and second perpendicular on frame. Compass mounted centrally, divided to 1 degree; locking bar. Horizontal circle subdivided to 30’; 2 verniers and microscopes. Clamp and tangent screws for vernier plate and horizontal circle. 3 levelling feet on tribrach limbs onto a clamped base plate. Plumb-bob (not original: marked ‘1943’ and with a crown). Erecting eyepiece. Spare eye glass in aluminium case. 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:42882
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