Accession No

0474

Brief Description

cover glass micrometer, for measuring the cover glass on a mounted specimen, 1900 (c)

Origin

Maker

Class

microscopes

Earliest Date

1870

Latest Date

1929

Inscription Date

Material

metal (brass, steel); enamel; glass

Dimensions

length 83mm; breadth 58mm; thickness 26mm

Special Collection

Robert Whipple collection

Provenance

Purchased from T.H. Court on 05/03/1929.

Inscription

Description Notes

Brass plate on 3 turned brass feet; steel jaws at top end on a steel spring with fussee chain; slot through bottom of plate with a knob handle to the spring. Fussee chain driven index moving over circular scale painted onto white enamel face divided (0)-90 x 4 by 10 to 2 (and to 1 by dots), and 360 at top. Dial diameter = 50mm.

Complete

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:43156