Accession No

1616

Brief Description

beam compass with micrometer, by Baradelle, French, 2nd half 18th Century

Origin

France; Paris

Maker

Baradelle

Class

drawing

Earliest Date

1750

Latest Date

1800

Inscription Date

Material

metal (steel, brass)

Dimensions

overall length 155mm; breadth 30mm; height 57mm; micrometer scale diameter 30mm; max radius of points 87.5mm

Special Collection

Provenance

Purchased from Francis Roux-Devillas, 12 Rue Bonaparte, Paris, France, in 07/1972.

Inscription

‘Baradelle AParis’ (micrometer scale)

Description Notes

Steel beam, screws and end-plates and points. All other fittings brass. Brass knurled screw turns lead screw and pointer over brass micrometer scale; graduated 0 - 100, numbered by 10, divided to 1. Steel points held by wing nuts. Wing nuts fastening the sliding point holders in position on the beam.

Condition: fair.

References

Events

Description
Micrometer
Micrometers were used mainly by astronomers and microscopists to measure objects. They were first devised in about 1609 and used the exact number of turns of a screw to measure small distances. Micrometers were inserted into the path of a telescopes and microscopes, and were also used to accurately measure quadrant scales.

Early examples of the micrometers used in telescopes were calibrated geometrically using a piece of card at a distance of about 200m with lines of known separation on it. However, this introduced inaccuracies of a few seconds of arc due to the closeness of the card compared with the distance of real observations. It was not until 1672 that this problem was overcome and accurate calibration was possible.

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

FM:40241