Accession No

3058

Brief Description

plane table alidade, by J. H. Steward, English, 1900 (c)

Origin

England; London; 406 Strand

Maker

J. H. Steward

Class

surveying

Earliest Date

1900

Latest Date

1900

Inscription Date

Material

metal (brass); glass; hide (leather)

Dimensions

case length 210mm; breadth 96mm; thickness 31mm

Special Collection

Steward collection

Provenance

Collection purchased from member of the Steward family, 1974.

Inscription

‘’J H Steward 406, Strand LONDON’
‘No 14
SOLE MAKER
PATENT’

Description Notes

Brass; black oxide finish. Rule with compass dial at one end. Trough compass within brass dial graduated 0-360˚ to 1˚. 16 points. Bubble level along axis of trough. Hinged mirror over with slit sight above. Hinged window sight at far end of rule. Rule graduated along bevelled sides “Yds 6INS to a MILE” 0-13 and “HORIZL EQUIVS NORMAL” 1-35˚.
Fitted leather case.

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:44515