Accession No
1917
Brief Description
dynameter, by Dollond, English, 1800 (c)
Origin
England; London
Maker
Dollond
Class
astronomy; optical
Earliest Date
1800
Latest Date
1800
Inscription Date
Material
metal (brass); glass; wood; paper; cloth (velvet)
Dimensions
length 56mm; breadth 24mm; depth 25mm case length 66mm; breadth 50mm; height 32mm
Special Collection
Cavendish collection
Provenance
Transferred from the Cavendish Laboratory, University of Cambridge in 08/1974. From the Wollaston Collection.
Inscription
‘Dollond
London’
Description Notes
Divided lens in brass mount, semi-lenses movedby knurled screw with drumhead divided on brass [0] - 100, numbered by 10, graduated to 1. Screw telescope attachment with two lenses.
Fitted wooden case lined with blue velvet and covered with red paper; brass hinges and hook fasteners.
Condition good; 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:39685
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