Accession No

2184

Brief Description

plane table alidade, tentatively attributed to E. R. Watts and Son, English, 1930 (c)

Origin

England; London [based on attributed maker]

Maker

E. R. Watts and Son Ltd. [tentative attribution]

Class

surveying

Earliest Date

1930

Latest Date

1930

Inscription Date

Material

metal (alloy)

Dimensions

length 405mm; breadth 66mm; height 88mm

Special Collection

Provenance

Transferred from Department of Geography, University of Cambridge, Cambridge, England, 05/1969.

Inscription

‘GEO.SCH. CAMB. UNIV. No. 6.’

Description Notes

Metal alloy with telescopic sights. Base divided into 12”. 1-0-11. Parallel ruler. Fixed focus telescope; partially retractable cross wire. Adjustable aperture.

References

Events

Description
Plane table alidade
A plane table is a flat square board, with a piece of paper attached to the top surface on top of which an alidade (sighting rule) is secured. The apparatus also requires a magnetic compass for orientation.

This allows for one of the most direct and convenient methods of surveying. Initially, a point is drawn to represent the first surveying station. Lines of sight to certain objects can then be taken with the alidade are marked on the paper using the rule. The table is then moved to the second location and oriented in the same way using the compass. The distance moved is represented on the paper by an appropriate scale. The same lines of sight are then taken again and the intersects of the two sight lines show where the object is. This process allows a plan of the site to be created.

18/10/2002
Created by: Saffron Clackson on 18/10/2002

FM:43382