Accession No
3680
Brief Description
recording micrometer, by John Browning, English, 1865 (c)
Origin
England; London
Maker
Browning, John
Class
optical
Earliest Date
1865
Latest Date
1865
Inscription Date
Material
metal (wire, steel); glass; wood
Dimensions
box length 347mm; breadth 116mm; height 75mm
Special Collection
Provenance
Purchased from Christie’s, South Kensington, London, England; lot 137, 19/11/1987.
Inscription
‘John Browning London’ (on head of instrument)
Description Notes
Browning called this instrument “Campbell’s spectrograph”, and it is for fitting to the eye-end of a spectrometer. In addition to the usual micrometer head linked to an index wire, a long screw carries the articulated mount for a steel point, by which the observer marks lines on a smoked glass plate. In a fitted wooden box. The key to the fitted box is inside the box.
Incomplete (missing glass slide)
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:44798
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