Accession No

2468

Brief Description

3-inch transit theodolite by Troughton and Simms, c.1915

Origin

London; England

Maker

Troughton & Simms

Class

surveying

Earliest Date

1915

Latest Date

1915

Inscription Date

Material

metal (brass, other); glass; wood

Dimensions

box length 291mm; breadth 249mm; height 155mm; horizontal circle diameter 90mm; height 229mm; telescope length 201mm

Special Collection

Provenance

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

Inscription

‘TROUGHTON & SIMMS Ltd
LONDON’ (horizontal circle)

Description Notes

Metal alloy construction with brass screws. Telescope with rack and pinion focus moving the objective. Inverting, sliding eyepiece. Cross hairs; ray shade. Telescope transits over eyepiece. Graduated bubble mounted over axis outside vertical circle. Vertical circle with silvered scale divided 0 - 90 - 0 - 90 - 0˚ subdivided to 30´ of arc; read by opposing verniers and microscopes to 1´ of arc. Clamp and motion screws for vertical circle and clipping screws. ‘A’ frame. Single bubble level mounted on horizontal circle. Horizontal circle with silvered scale divided 0 - 360˚ and read by verniers and hinged microscopes to 1´ of arc. Clamp and motion screws for vernier scale and horizontal circle. 3 levelling feet on tribrach limbs. Trough compass slots onto base of horizontal circle; silvered scale divided 5˚ - 0 - 5˚. Plumb-bob. Trivet base clamps onto feet and has threaded aperture for attachment onto tripod.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:42904