Accession No

0577.2

Brief Description

cover glass micrometer, by Ross, English, late 19th century to early 20th century

Origin

England; London

Maker

Ross

Class

microscopes

Earliest Date

1859

Latest Date

1930

Inscription Date

Material

metal (brass, steel)

Dimensions

box length 172mm; breadth 83mm; height 108mm

Special Collection

Robert Whipple collection

Provenance

Purchased from T.H. Court on 01/03/1930.

Inscription

‘Ross, London’

Description Notes

Brass; turned stand and pillar to pierced brass plate; steel index with a notch; the buff end pressing onto a vertical plate screwed to the horizontal surface. Index moves over a scale divided 0-2 by 1 to 1/10 where 1/10 = 1/1000” scale marked 1/100 and 1/50 at the centre and the far end.

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:42758