Accession No

2465

Brief Description

5-inch transit theodolite, by C. Baker, English, c. 1895

Origin

England; London; 244 High Holborn

Maker

C. Baker

Class

surveying

Earliest Date

1895

Latest Date

1895

Inscription Date

Material

metal (brass, other); glass; wood

Dimensions

box length 355mm; breadth 320mm; height 189mm; horizontal circle diameter 131mm; height 321mm; telescope length 259mm

Special Collection

Provenance

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

Inscription

‘C. Baker. 244 High Holborn London 3342’ (on telescope)
‘Adjusted April 10 1906’ (trade label in box)

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 to 1/10”. Vertical circle with silvered scale divided 0 - 90 - 0 - 90 - 0˚, subdivided to 30’ of arc; read by 2 opposing veniers and microscopes to 1’ of arc. Also divided 30 - 0 - 30 Diff of Hypo and Base. Clamp and motion screws. Clipping screws for levelling telescope. ‘A’ frame supports axis with adjustable bearings. Compass mounted on horizontal plate; 8-point silvered rose, 0 - 260˚ subdivided to 1; locking bar operated by screw. One bubble mounted on horizontal plate, second perpendicular on frame. Horizontal circle with silvered scale divided 0 - 360˚ and read by 2 verniers and hinged microscopes to 1’ of arc. Clamp and motion screws for vernier plate and horizontal circle. 3 levelling feet on tribrach limbs. Trivet plate with clamps for levelling feet. Digonal eyepiece. Erecting eyepiece. Dark glass. Fitted wooden box.

Condition

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:42910