Accession No

3681

Brief Description

moving-wire eyepiece micrometer, by John Browning, English, 1870s

Origin

England; London

Maker

Browning, John

Class

optical

Earliest Date

1870

Latest Date

1880

Inscription Date

Material

metal (brass, silver); glass

Dimensions

length 139mm; breadth 43mm; thickness 44mm

Special Collection

Provenance

Purchased from Christie’s, South Kensington, London, England, 19/11/1987.

Inscription

‘John Browning
London.’ (next to eyepiece fitting)

Description Notes

Lacquered brass Filar micrometer with (screw-fit) spectroscope or telescope fitting and silvered scales.
(Scale divided 0-9 by 1. Vertical scale turned by knurled screw with extended handle, divided 0-[100], numbered by 5, divided to 1. Short brass rod extends from far end; 10-2-2000).

Condition: good; incomplete (cross-wires and eyepiece missing (cover for eyepiece missing?; 10-2-2000)).

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:42839