Accession No

2583


Brief Description

12-inch transit theodolite, by Troughton and Simms, English, 1898


Origin

London; England


Maker

Troughton and Simms


Class

surveying


Earliest Date

Jan. 1, 1898


Latest Date

Dec. 31, 1898


Inscription Date


Material

metal (brass, 2 white metals, 2 others); glass; wood (mahogany); liquid; paper


Dimensions

height (on tripod) 1580mm; breadth 905mm; depth 900mm; horizontal circle diameter 320mm; telescope length 533mm


Special Collection


Provenance


Inscription

‘TROUGHTON & SIMMS
LONDON’ (on outer horizontal ring)
‘1092
·
Ι
1898’ (on outer horizontal ring)


Description Notes

Grey-finished metal alloy (brass?) construction. Telescope focussed by screw protected beneath screw-on metal cap. Telescope transits over eyepiece; counter-balanced. Folding sights on both sides. Eyepiece mounted on detachable plate fixed by means of 4 screws and can be moved across field of view by adjusting screw. Paper lining between eyepiece plate and instrument. Clamp for vertical circle over axis. Vertical circle with silvered scale divided 0 - 360˚ numbered by 2 subdivided to 5´. Read by 2 micrometer microscopes to 1˝. Third microscope with no micrometer. Long bubble, mounted between micrometers, graduated 0 - 50 in 1/10˝; enclosed within glazed case. Spoked horizontal circle moves manually, independently from main frame, mounted insed and over protecting outer ring. Silvered scale divided 0 - 360˚ read by 2 micrometers to 1˝. Third microscope with no micrometer. Clamp and screw on external ring controls azimuth motion. 3 levelling feet on tribrarch limbs. Long bubble on one side of base of frame. Second case for bubble on opposite side. Mahogany frame tripod.

Condition good; complete


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:44264

Images (Click to view full size):