Accession No

0418

Brief Description

brass altazimuth theodolite on wooden stand, by Heath and Wing, English, 1740 - 1771

Origin

England; London

Maker

Heath and Wing

Class

surveying

Earliest Date

1740

Latest Date

1771

Inscription Date

Material

metal (brass, steel, white metal); wood (mahogany); glass

Dimensions

Horizontal circle diameter 140mm; Telescope length 260mm; height (including base) 280mm

Special Collection

Robert Whipple collection

Provenance

Purchased from T.H. Court in 09/1928.

Inscription

‘Heath & Wing, London.’ (on Horizontal Circle)
‘Diff: Hypo: & Base.’ (on Vertical vernier arm)

Description Notes

Brass theodolite. Erecting telescope. Cross hairs. Telescope mounted on frame (marked ‘Deprn’ and ‘Elevn’) extending from centre of vertical, pierced semi-circle. Bubble mounted on axis of frame. Vertical semi-circle fixed rigidly to horizontal circle. 3 scales. Outer scale of degrees 90 - 0 - 90 - 0 numbered by 10 subdivided to 1 read by vernier on telescope frame to 5’ of arc. Middle scale graduated to 100 - 0 and 0 - 100 feet numbered by 10 subdivided to 2. Inner scale graduated 25 - 0 - 25 links numbered ‘25’, ‘20’, ‘25’, ‘10’, ‘8’, ‘6’, ‘4’, ‘2’ subdivided to 1. Vernier scale and therefore vertical motion of the telescope controlled by pinnion operating on toothed outer edge of vertical semi-circle. Centrally mounted compass with 8 point silvered rose calibrated 0 - 90 - 0 - 90 - 0 numbered by 10 subdivided to 1 twice in single degrees. Bubble set in compass face. Horizontal circle graduated [0] - 360° numbered by 10 subdivided to 1 and read by vernier to 5’ of arc. Inner scale partially showing marked ‘breadth’, numbered by 10 subdivided to 1. Rack and pinnion motion screw.

Condition fair (rack and pinion for horizontal circle broken); complete

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:40196