Accession No

2166

Brief Description

5-inch transit theodolite, by Cary, English, 1915

Origin

England; London

Maker

Cary

Class

surveying

Earliest Date

1915

Latest Date

1915

Inscription Date

1915

Material

metal (brass, other); glass; wood

Dimensions

box 1 length 345mm; breadth 335mm; height 204mm box 2 length 410mm; breadth 215mm; height 245mm; horizontal circle 145mm; height 350mm; telescope length 290mm

Special Collection

Provenance

Transferred from Department of Geography, University of Cambridge, Cambridge, England, 05/1969.

Inscription

‘Cary LONDON No 166 1915’ (on horizontal circle)
‘Cary PORTER 5” MISCROMETER THEODOLITE’ (on outside of box)

Description Notes

Black finished metal alloy with brass screws.
Inverting telescope with rack and pinion focus moving the objective. Eyepiece with secondary focus. Bubble mounted on the outside of the vertical circle. Telescope transits over the eyepiece. Vertical circle graduated on a silver scale 0 - 360˚ and read by micrometer microscopes to 10” of arc and then by estimation. Clamp and motion screws for vertical circle. Clipping screws. Hollow axis which can be illuminated.
‘A’ frame with axis in ‘Y’ mounts held in place by metal bar. Bubble on frame and second on horizontal plate. Horizontal circle almost completely enclosed and read by micrometer microscopes to 10’ of arc. Clamp and motion screws for the horizontal circle and vernier plate. 3 levelling feet on tribrach limbs.
Trough compass slots onto base of horizontal circle; silvered scale divided 5˚ - 0 - 5˚; locking bar. Prismatic artificial horizon. Trivet base for attachment to tripod. Lens cover and ray shade. Dark lens. spare eyepiece. Diagonal eyepiece. Aluminium jar containing mercury. Lamp for illumintaing axis. Spare cross hairs. Couter weight for artificial horizon. Diagonal erecting lens. Diagonal inverting lens.
2 mahogany boxes. Trade labels and 2 adjustement labels inside box: 5.10.1950 and 24.3.1952 (micrometers only)

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:42912