Accession No

2474

Brief Description

5-inch transit theodolite (incomplete), by A. G. Thornton, English, 1900 (c)

Origin

England; Manchester

Maker

A. G. Thornton

Class

surveying

Earliest Date

1900

Latest Date

1900

Inscription Date

Material

metal (brass, other); glass; wood

Dimensions

box length 345mm; breadth 305mm; height 192mm; Horizontal circle diameter 140mm; height 131mm

Special Collection

Provenance

Transferred from Department of Engineering, University of Cambridge, Cambridge, England, 09/1979.

Inscription

‘A.G. Thornton Manchester’ (on compass face)

Description Notes

Vertical circle, vernier plate and microscopes in separate pieces; telescope missing. Metal alloy construction with dark green finish and brass screws. Vertical circle with silvered scale divided 0 - 90 - 0 - 90 - 0˚ subdivided to 30´ of arc. Diff of Hypo and Base scale divided 30 - 0 - 30. Vernier plate reading to 1´ of arc. Clamp, motion and clipping screws. Pair of reading microscopes. ‘A’ frame with bubbles mounted on frame and limb. Centrally mounted compass with silvered 8-point rose divided 0 - 360˚; locking bar. Horizontal circle with silvered scale divided 0 - 360˚ subdivided to 30´ of arc; read by 2 opposing verniers to 1´ of arc; 1 reading microscope. Clamp and motion screws for horizontal circle and vernier plate. 3 levelling feet on tribrach limbs. Clamped base plate with central thread for attachment to tripod. Fitted wooden box with trade labels.

Condition; incomplete

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:43327