Accession No
2528
Brief Description
plane table and alidade, alidade by Cary, English, 1900 (c)
Origin
England; London
Maker
Cary [alidade]
Class
surveying
Earliest Date
1900
Latest Date
1900
Inscription Date
Material
metal (brass, oxidized brass); wood (mahogany, ebony); rope (string); cloth (canvas, felt)
Dimensions
plane table length 432mm; breadth 379mm; alidade length 457mm
Special Collection
Provenance
Purchased from Historical Technology Inc., 6 Mugford Street, Marblehead, Mass. 01945, USA, 01/10/1979.
Inscription
‘Cary, London.’ (on alidade)
Description Notes
Mahogany plane table bound with brass corner plates, with brass threaded mount for tripod. Slot for compass. Table shaped to take separate rigid ebony surround, bound with brass, half graduated in degrees 0 - 90 - 0 numbered by 10 subdivided to 30’; half graduated in inches, unnumbered, divided to 1/10th and 1/12th. Divisions on both faces of surround. Four brass clips to secure surround. Brass alidade with oxidized brass pinhole and window sights; bevelled edge of alidade divided 0 - 14 inches numbered by 1 graduated to 1/20th. First inch subdivided to 1/100th of an inch by diagonals and final half inch divided to 1/200th by diagonals. Felt lined mahogany box for alidade and canvas bag for plane table.
Condition good; complete
References
Joshua Nall; ‘Survey Instruments in India’; 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/survey-instruments-india
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:39610
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