Accession No

2459

Brief Description

4-inch transit theodolite, by B. J. Hall and Company Ltd., English, 1916

Origin

England; London

Maker

B. J. Hall and Company Ltd.

Class

surveying

Earliest Date

1916

Latest Date

1916

Inscription Date

1916

Material

metal (brass, one other); glass; wood

Dimensions

length 233mm; breadth 145mm; height 278mm; box length 325mm; breadth 273mm; height 175mm

Special Collection

Provenance

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

Inscription

‘B J Hall and Co Ltd London No 128 1916’ (on compass face)

Description Notes

Metal alloy with black fininsh and brass screws. Telescope with rack and pinion focus moving the objective. Cross hairs; ray shade. Principal bubble mounted to the left of the vertical circle; graduated to 1/10”. Adjusted by clipping screws. Vertical circle with scale subdivided to 30’ of arc and read by 2 opposing vernier and microscopes. Clamp and motion screws for vertical circle. ‘A’ frame with one bubble mounted on the horizontal circle and second perpendicular on frame. Compass mounted centrally, with silvered scale divided 0 - 360, subdivided to 1 degree; locking bar. Horizontal circle subdivided to 30’ of arc; read by 2 verniers and microscopes. Clamp and motion screws for vernier plate and horizontal circle. 3 levelling feet on tribrach limbs through a trivet base plate. Spare erecting lens. Dark eye glass. Aluminium case (empty). 2 plumb-bobs (one sexagonal alloy; other brass and stamped ‘Crown AM 1944’). Fitted wooden box with carrying bag.

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:42884