Accession No
0399.1
Brief Description
dynameter, Ramsden type, by Matthew Berge, English, c. 1810 [with box, see Wh.0399.2]
Origin
England; London
Maker
Berge, Matthew
Class
astronomy; optical
Earliest Date
1800
Latest Date
1819
Inscription Date
Material
metal (brass); glass
Dimensions
overall length 339mm; diameter 28mm
Special Collection
Robert Whipple collection
Provenance
Purchased by Robert Stewart Whipple from T.H. Court on 28/09/1928.
Inscription
Berge London
late Ramsden (eyepiece)
Description Notes
dynameter (aka telescope eyepiece micrometer), Ramsden type, by Berge, English, c. 1810. [with box, see Wh.0399.2]
Telescope eyepiece with divided lens micrometer, brass. Three screw-fit sections. the first with attachment to telescope and draw tube arrangement, single lens in threaded brass mount. 2nd section with divided lens micrometer, the semi-lenses apparently mounted on half cylinders which pivot about object end, moved in opposite directions by screw with drumhead divided on brass 0 - 100, numbered by 10, graduated to 2, and transverse scale 0 - 9. 3rd section with 2 lenses in internaltube and screw-fit eyestop with pivoted cover.
With fitted box - see Wh.0399.2.
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 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:39688
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