Accession No

2470

Brief Description

6-inch transit theodolite, by C. Baker, English, c. 1890

Origin

England; London; 244 High Holborn

Maker

C. Baker

Class

surveying

Earliest Date

1890

Latest Date

1890

Inscription Date

Material

metal (brass, other); glass; wood

Dimensions

height 495mm; depth 210mm; breadth 207mm; horizontal circle diameter 170mm; telescpe length 281mm; height 365mm

Special Collection

Provenance

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

Inscription

‘Baker. 244 High Holborn, LONDON’ (on compass face)

Description Notes

Metal alloy construction with brass screws. Telescope with rack and pinion focus moving the objective and inverting eyepiece. Bubble mounted over the telescope, graduated. Vertical circle with silvered scale divided 0 - 90 - 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. Clipping screws for levelling telescope. ‘A’ frame with bearing adjustment for axis. Compass mounted centrally on the horizontal plate; 8-point silvered rose with scale divided 0 - 360˚; locking bar operated by screw. One bubble mounted on horizontal plate, second perpendicular on frame. Horizontal circle divided 0 - 360˚ subdivided to 20´ and read by verniers to 20˝ of arc. Clamp and motion screws for vernier plate and horizontal circle. 4 levelling feet between parallel plates. Erecting lens. Fitted wooden box.

Condition (rusty)

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:42886