General Roy's standard scale by Jonathan Sisson, 1742

General Roy's 42 inch standard scale, in brass, made by J General Roy's 42 inch standard scale, in brass, made by J General Roy's 42 inch standard scale, in brass, made by J General Roy's standard scale by Jonathan Sisson, 1742

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Creative Commons LicenseThis image is released under a CC BY-NC-SA 4.0 Licence

Buy this image as a print 

Buy

License this image for commercial use at Science and Society Picture Library

License

Creative Commons LicenseThis image is released under a CC BY-NC-SA 4.0 Licence

Buy this image as a print 

Buy

License this image for commercial use at Science and Society Picture Library

License

Creative Commons LicenseThis image is released under a CC BY-NC-SA 4.0 Licence

Buy this image as a print 

Buy

License this image for commercial use at Science and Society Picture Library

License

General Roy's 42 inch standard scale, in brass, made by J
Science Museum Group
© The Board of Trustees of the Science Museum

General Roy's 42 inch standard scale, in brass, made by J
Science Museum Group
© The Board of Trustees of the Science Museum

General Roy's 42 inch standard scale, in brass, made by J
Science Museum Group
© The Board of Trustees of the Science Museum

Science Museum Group Collection
© The Board of Trustees of the Science Museum

General Roy's 42 inch standard scale, in brass, made by J. Sisson and divided by Bird with wooden case. Used for Hounslow Base Line in the "Great Survey made by J. Sisson of England", 1784 and divided by Bird 1742

This scale was made by Jonathan Sisson (fl 1736-1788) and divided by John Bird in 1742. Later in 1784, Major-General Roy (1726-1790) used this scale when he was set the task of laying out a base line on Hounslow Heath, for the first survey of Britain by triangulation. This enabled him to fix the relative positions of Greenwich and Paris observatories with greater accuracy than before. This laid the foundation of the first accurate maps of Great Britain.

Details

Category:
Weighing & Measuring
Object Number:
1931-988
Materials:
brass (copper, zinc alloy)
type:
rules (measuring devices) and linear standards
credit:
Board of Trade

Parts

William Roy’s standard scale, 1742

William Roy’s standard scale, 1742

42-inch standard scale marked with a standard yard, made by Jonathan Sisson and divided in 1742 by John Bird, both based in the Strand, London. The scale was owned by surveyor General William Roy and used by him whilst conducting measurements of a baseline at Hounslow Heath in 1784.

More

William Roy led the Anglo-French project to determine by triangulation the relative positions of the Paris and Greenwich observatories. The fist step was the accurate measurement of a baseline; Hounslow Heath was the location selected by Roy.

Accuracy was crucial for this project, as even tiny errors would multiply when measurements spread across the country. Before beginning his measurements in 1784, surveyor William Roy ensured that his scale corresponded with the standard yard held at the Royal Society by comparing them carefully using a microscope. His investigations showed that the scales match exactly. He used the scale, which has a standard yard marked on it, to confirm the lengths of wooden rods used to verify an initial measurement of the baseline with a surveying chain.

Measurements:
Overall: 14 mm x 1090 mm x 7 mm, 0.74 kg
Materials:
brass (copper, zinc alloy)
Object Number:
1931-988 Pt1
type:
linear measure standard
Image ©
The Board of Trustees of the Science Museum
Case for William Roy’s standard scale, 1742

Case for William Roy’s standard scale, 1742

Case for 42-inch standard scale marked with a standard yard, 1742, inscribed: ‘General Roy’s 3-Feet Standard’. The scale was owned by surveyor William Roy and used by him whilst conducting measurements of a baseline at Hounslow Heath in 1784.

More

William Roy led the Anglo-French project to determine by triangulation the relative positions of the Paris and Greenwich observatories. The fist step was the accurate measurement of a baseline; Hounslow Heath was the location selected by Roy.

Accuracy was crucial for this project, as even tiny errors would multiply when measurements spread across the country. Before beginning his measurements in 1784, surveyor William Roy ensured that his scale corresponded with the standard yard held at the Royal Society by comparing them carefully using a microscope. His investigations showed that the scales match exactly. He used the scale, which has a standard yard marked on it, to confirm the lengths of wooden rods used to verify an initial measurement of the baseline with a surveying chain.

Materials:
wood (unidentified)
Object Number:
1931-988 Pt2
type:
instrument case
Image ©
The Board of Trustees of the Science Museum