Accession No
2160
Brief Description
4-inch transit theodolite by W. Ottway and Company, English, c. 1917
Origin
England; London; Ealing
Maker
W. Ottway and Company Ltd.
Class
surveying
Earliest Date
1917
Latest Date
1917
Inscription Date
Material
metal (brass, 1 other); glass
Dimensions
height 325mm; length 235mm; breadth 175mm
Special Collection
Provenance
Transferred from Department of Geography, University of Cambridge, Cambridge, England, 05/1969.
Inscription
‘W. OTTWAY & Co Ltd
ORION WORKS
EALING No. 11077’ (on base of ‘U’ frame)
Description Notes
Metal alloy with black fininsh and brass screws. Telescope with rack and pinion focus moving the objective. Inverting, sliding eyepiece. Ray shade; cross hairs. Bubble mounted outside vertical circle graduated in 1/10”. Vertical circle with silvered scale divided 0 - 90 - 0˚ twice, subdivided to 20’ of arc; read by 2 opposing verniers and microscopes to 20” of arc (scale badly tarnished). Clipping screws. Vertical clamp and motion screws. Telscope mounted on ‘U’ frame attached to horizontal circle. Bubble mounted over horizontal circle with second in frame. Horizontal circle enclosed and read by micrometer microscopes. Clamps and motion screws for horizontal scale and horizontal circle. 3 levelling feet on tribrach limbs. Trivet base plate with clamps and central thread for attachment to tripod. Trough compass slots onto base of horizontal circle; silvered scale divided 5˚ - 0 - 5˚.
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:42915
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