Accession No

2464

Brief Description

5-inch transit theodolite, by E. R. Watts and Son, English, 1915 (c)

Origin

England; London

Maker

E. R. Watts and Son

Class

surveying

Earliest Date

1915

Latest Date

1915

Inscription Date

Material

metal (brass, other); glass; wood

Dimensions

box 1 length 347mm; breadth 210mm; height 173mm box 2 length 390mm; breadth 210mm; height 230mm; horizontal circle diameter 146mm; telescope length 250mm; height 345mm

Special Collection

Provenance

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

Inscription

‘E.R. WATTS and Son London 1903 No 115’ (horizontal plate)

T.L [lid of box, outside]

Description Notes

Metal alloy construction with brass screws. Inverting telescope with rack and pinion focus moving the objective. Cross hairs; ray shade. Bubble mounted over axis outside vertical circle. Vertical circle with silvered scale subdivided to 20’ of arc; read by opposing vernier scales and microscopes. Vertical clamp inside the frame with vertical motion screw. Clipping screws. ‘A’ frame on horizontal plate with 2 mutually perpendicular bubbles. Horizontal circle with silvered scale subdivided to 20’ of arc and read by 2 opposing verniers and microscopes to 30” of arc. Clamp and motion screws for vernier plate (with springs) and horizontal circle. Slot for trough compass under horizontal plate. 3 levelling feet on tribrach limbs. Trivet plate clamps onto feet and has threaded aperture for attachment to tripod. Diagonal lens. Erecting lens. Trough compass with silvered scale divided 5˚ - 0 - 5˚. Plumb-bob.

2 Fitted wooden boxes.

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:42909