Filar micrometer

Title

Filar micrometer

Subject

Astronomy
Measuring instrument
Optical instrument

Description

Wood, brass, glass

Wooden box (dimensions) with hinged lid, with 4 colored shades (2 green, 2 red), 3 eyepieces with adapter, one smaller eyepiece with adapter, accessories for light.

“Its filar position micrometer consists essentially of a position circle 6.3 inches in diameter, graduated on silver to half degrees and read by to verniers to tenths of a degree and a very accurately threaded screw, carrying a light frame holding the micrometer wires. Whole revolutions of the screw are read by a toothed wheel and fractional parts of the screw are given by a drum of 2.5 inches diameter whose circumference is graduated to hundredths. Tenths of divisions are readily estimated. The micrometer box is moveable in position angle, the entire system of threads fixed and movable is carried ‘in distance’ by a screw without graduations and the eye piece is adjusted to the center of the fields by a still different screw.”

A filar micrometer is used for precision positional astronomy by measuring the separation or angular distance between two objects. In addition it can measure the position angle between them. They were often used to measure the angles and distances between double stars. Data gathered over long periods of time could demonstrate the orbit of one star about the other star. Micrometers are seldom used on modern astronomy having been replaced by newer techniques.

This micrometer came with the Equatorial. Stebbins used it to measure size of crater Linné during February 8, 1906 lunar eclipse. Cleaned by J.W. Fecker in 1954.

Creator

Warner & Swasey Company

Source

Myers, G.W. (1898) The Astronomical Observatory. Technograph. 11: 105-111.

Stebbins, J. (1906) Observations of the crater Linné during the lunar eclipse of February 8, 1906. Astronomical Journal. Vol. 25. No 587, p. 87-88.

Publisher

Astronomy Department, University of Illinois, Urbana, Illinois

Date

1896

Contributor

Michael Svec

Rights

Copyright Michael Svec

Format

image/jpg

Language

English

Type

physical object

Identifier

University of Illinois Observatory Collection A102
University ID 016717, obs 735

Coverage

University of Illinois Observatory, Urbana, Illinois

Files

filar micrometer
DSCN0121.JPG
DSCN0117.JPG

Tags

Citation

Warner & Swasey Company, “Filar micrometer,” University of Illinois Observatory Collection, accessed September 19, 2017, http://uiobservatory.omeka.net/items/show/4.

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