Accession No

1877


Brief Description

8-inch Everest theodolite and tripod, by Troughton and Simms, English, c. 1880


Origin

London; England


Maker

Troughton & Simms


Class

surveying


Earliest Date

Jan. 1, 1880


Latest Date

Dec. 31, 1880


Inscription Date


Material

metal (brass, 1 other); glass; wood


Dimensions

horizontal circle diameter 215mm; telescope length 130mm; height 245mm; box height 292mm; length 275mm; breadth 302mm


Special Collection


Provenance

Purchased from Antiques and Co., King Street, Cambridge in 12/1973.


Inscription

‘Troughton and Simms LONDON’ (horizontal circle)
‘C BAKER optician 244 HIGH HOLBORN LONDON’ (Box)


Description Notes

Metal alloy with brass screws.
Inverting telescope with rack and pinion focus moving the objective. Sliding eyepiece. Trough compass mounted with milled screws onto the top of the telescope; silvered scale divided 9˚ - 0 - 9˚. 2 vertical arcs with silvered scales divided 40 - 0 - 40; read by verniers and magnifying glasses to 30” of arc. Bubble mounted on the vernier plate. Clipping screws. Clamp and motion screws on vernier plate.
Telescope supported on arms from central pillar mounted on horizontal vernier plate. Bubble on the support axis. Horizontal silvered circle graduated 0 - 360˚ and to 10’ of arc. Read by 3 vernier plates and single swivelling magnifying glass. Clamp and motion screw for vernier plate and the horizontal circle. 3 levelling feet on tribrach limbs.
Fitted wooden box containing erecting lens, plumbob, trivet plate with clamp and central thread for attachment to tripod, lens cover, and spare cross hairs (in cardboard box)


References

Joshua Nall; ‘Science in the Field’; Explore Whipple collections online article; Whipple Museum of the History of Science; University of Cambridge; 2020: https://www.whipplemuseum.cam.ac.uk/explore-whipple-collections/astronomy-and-empire/science-field


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:42924

Images (Click to view full size):