Accession No

2163

Brief Description

plane table alidade, 1920 (c)

Origin

Maker

Class

surveying

Earliest Date

1920

Latest Date

Inscription Date

Material

metal (alloy); glass

Dimensions

length 400mm; breath 91mm; height 75mm

Special Collection

Provenance

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

Inscription

‘GEO SCH. CAMB. UNIV. No 10’

Description Notes

Metal alloy; black finish; parallel rule; bubble on base. Graduations along bevelled edge 0-1-11”. Telescopic sight; ray shade; sliding eyepiece focus; sights along upper edge of telescope. Bubble with fine motion screw mounted parallel to telescope with ‘degrees of depression, elevation’ scale graduated 10-0-10. Bubble read by hinged mirror from eyepiece. Clamps for telescope on either side of axis.

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:43383