Accession No
2848
Brief Description
transit theodolite, used as a bench demonstration instrument for practical class work at the Sedgwick Museum, by W. and L. E. Gurley, U.S.A., 1945 (c)
Origin
U.S.A.; New York; Troy
Maker
W. and L.E. Gurley
Class
surveying
Earliest Date
1945
Latest Date
1945
Inscription Date
Material
metal; glass; plastic
Dimensions
box height 418mm; breadth 245mm; depth 285mm; horizontal circle diameter 161mm; overall height 335mm; telescope length 252mm
Special Collection
Provenance
Transferred from Sedgwick Musuem, Department of Earth Sciences, University of Cambridge, Cambridge, England, 05/1982. Purchased at Army Surplus stores in the late 1940s or 1950s.
Inscription
‘W. & L.E. GURLEY
TROY, N.Y., U.S.A.’ (on compass face)
‘U.S.’ (on compass face)
‘Beaman Stadia Arc’ (on vertical circle)
‘W. & L.E. GURLEY, TROY, N.Y., U.S.A.’ (on vertical supports)
‘44317’ (on horizontal plate)
‘GURLEY
ENGINEERING INSTRUMENTS
TROY, N.Y., U.S.A.’ (plate on box)
Description Notes
Black transit theodolite with double ‘A’ frame. Telescope with cross hairs focussed by knurled screw moving objective, eyepiece focus by milled ring; screw-on plastic eyestop; push-fit objective cover; hanging level. Vertical circle with radial supports has silvered scale divided 0 - 90 - 0 - 90 - 0 numbered by 1˚ subdivided to 30´; read by type-A vernier to 1´. Clamp and slow motion screws. Horizontal plate with 2 bubble levels. Large central glazed compass marked with 4 cardinal points, with silvered scale divided 0 - 90 - 0 - 90 - 0, and other subsidiary scales; clamp for needle operated by milled screw. Enclosed horizontal circle divided 0 - 360 (in both directions) numbered by 1˚ subdivided to 30´; read through 2 glazed apertures with 2 type-A verniers and white reflectors (marked ‘A’ and ‘B’) reading to 1´. Clamp and tangent screws. Flat tripod base with 4 levelling screws and plate for tripod mount. Fitted wooden box with objective hood, hand lens, oil bottle and tools, and right-angled eyepiece. 3 instruction labels. Painted on box: ‘Sedgwick Museum. Downing Street, Cambridge’ and ‘S.8.’.
Condition
References
Events
Description
The theodolite is a relatively simple tool used for measuring angles, both horizontal and vertical. It works 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 that is still used today.
FM:44118
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