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Filar telescope micrometer, 1900 - 1930
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Object statement
Astronomical measuring instrument, filar telescope micrometer, brass / glass, made by Ross and Dollond & Sons, London, England, 1900-1930, used at Sydney Observatory, New South Wales, Australia, 1926-1944
This micrometer was used at Sydney Observatory in conjunction with the 11.4 inch telescope (H9886). It was later adapted to allow it to be fitted to the sighting telescope of Sydney Observatory's Astrographic telescope.

Filar micrometers are used in astronomy to measure small angles and arcs. The device uses two very fine parallel wires or threads that can be manipulated by the observer to take very minute measurements. One wire is placed over a viewed object and the other wire is moved by a screw mechanism over the other object; the distance in between can then be measured using the scale on the micrometer. At one time spiders' silk was used for the cross hairs on a micrometer, until new technology allowed finer and more durable wires to be produced. Instruments such as this one have been superseded, but they were historically most commonly used to measure the distance between double stars.

This filar micrometer remains of national significance due to its pioneering role in Australian science and its association with Australia's earliest astronomers. It is also of international significance due to its association with nineteenth century scientific instruments and their makers.

Written by Erika Dicker
Assistant curator, February 2008.
Filar telescope micrometer made by Ross of London mounted on a graduated circle made by Dollond and Sons.

The Dollond workshops in England produced quality precision and scientific instruments over a long period of time in the 19th century. A large number of scientific instruments in museum collections are signed with the Dollond signature; however it can be difficult to know which specific member of the Dollond family would have made the object. As the Dollond firm was so highly respected, numerous instruments were produced by others with misleadingly similar maker's marks such as Dolland.

John Dollond (1706-1761) began his working life as a textile weaver to support his family after the death of his father. He devoted his spare time to the study of mathematics and natural philosophy. Dollond raised his own family and continued in his weaving business, where he was eventually joined by his eldest son, Peter.

Peter Dollond (1730-1820) had adopted his father's passion for science and mathematics and quit the silk trade in the mid 1700s to commence his own business as an optician. He commenced business in 1750 and was only moderately successful until he was joined by his father, John, in 1752. After quitting the weaving trade, John Dollond wasted no time in putting his passion into practice and by 1753 was presenting his micrometer improvements to the Royal Society.

His micrometer, used in astronomy, allowed the user to determine the distance separating two objects observed through a telescope. John Dollond preferred this device to be used with a reflecting telescope, but his son soon adapted the device so it could also be used with a refracting telescope. This instrument is now know as a divided object-glass micrometer, and was one of the most useful instruments for measuring small angles in astronomy. The usefulness of this invention made the Dollond name instantly popular with both amateur and professional astronomers.

John Dollond, and the Dollond name, rose to more fame with his development of the achromatic lens, which corrected chromatic aberration by combining lenses made of different types of glass. This destroyed the surrounding fringe of colours that had previously made the images formed in a refracting telescope indistinct. This development was hugely beneficial to observing telescopes. John Dollond's achromatic lenses were presented to the Royal Society in 1758 , and he was awarded the society's highest award, the Copley Medal, for his achievements.

Through John and Peter Dollond's achievements, the Dollond name became one of prestige and quality in regard to scientific instruments in the mid 1700s. During this time, they were also commissioned to produce precision instruments for the Royal Observatory, which was a huge asset to a maker's name.

John Dollond was granted fellowship of the Royal Society in 1761 , the same year he died from apoplexy (stroke). Peter Dollond continued to work in the business alone, becoming optician to His Majesty and to His Royal Highness the Duke of York in 1763. In 1766 Peter Dollond was joined in the business by his younger brother, John Dollond (2), who left to pursue his own career in 1804.

Peter Dollond's nephew, George Huggins (1774-1852), joined him in business in 1804. George changed his name to George Dollond upon entering the partnership. The new partnership was extremely successful, with the Dollonds being described as the "most prestigious optical instruments makers in Britain" in the early 1800s.

George Dollond was elected to a fellowship of the Royal Society in 1819 and was an active participant in founding the Astronomical Society in 1820.

George Dollond took ownership of the business in 1820, upon the death of his uncle Peter, and was joined by his son George Huggins (2). As his father had done, half a century before him, George Huggins (2) changed his last name to Dollond upon entering the business. Upon George Dollond's (1) death in 1852, the Dollond business was taken over by his son, George Dollond(2).

The following is a list of dates and corresponding workshop addresses, found inscribed on Dollond instruments in museum collections. (please note this list may not be totally accurate but can be used as a rough guide):

John and Peter Dollond:
1750 to 1752= Vine Street, Spitalfields, London
1752 to 1763= Golden Spectacles and Sea Quadrant, near Exeter Exchange,
Strand, London.

Peter Dollond
1763 to 1766= at the Sign of the Prisms, London

1766 to 1795= 59 St. Paul's Churchyard, London

1795 to 1804= 35 Haymarket, London

Peter and George Dollond:
1804 to 1820= St Paul's Churchyard, London

George Dollond (1) George Dollond (2)
1820 to 1854= St Paul's Churchyard, London

George Dollond (2)
1854 to 1856= 61 Paternoster Row, London


Reference:
Arthur Thomas Malkin, The Gallery of Portraits with memoirs, Volume 3, London, 1834 pp 12-19
David Brewster, Treatise on the Kaleidoscope, 1819
J. A. Bennet, The Divided Circle, A history of instruments for astronomy navigation and surveying, Christies Ltd, England, 1987
Myles W Jackson, Spectrum of Belief, Joseph Von Fraunhofer and the craft of precision optics, MIT Press, USA, 2000
Webster Signature Database, available at: http://historydb.adlerplanetarium.org/signatures/
Julian Holland's work on scientific instrument makers, available at:
www.usyd.edu.au/museums/whatson/exhibitions/kater1.shtml

Written by Erika Dicker, Assistant Curator, February 2008.
The instrument was used at Sydney Observatory, Observatory Hill, Sydney, Australia.

The details of this instrument's use are obscure, but it may have been used originally with the Observatory's 11.4 inch telescope (H9886) before being later adapted for use with the astrograph (H10255). It is said to have been acquired by the Observatory when James Nangle was the Government Astronomer. Nangle was appointed Government Astronomer in 1926 and died in 1941.

 This text content licensed under CC BY-NC.

Description
Astronomical measuring instrument, filar telescope micrometer, brass / glass, made by Ross and Dollond & Sons, London, England, 1900-1930, used at Sydney Observatory, New South Wales, Australia, 1926-1944

Filar telescope micrometer mounted in the centre of a graduated circle fitted with two eyepieces. A screw gauge on one side of the micrometer turns a wheel with a graduated scale engraved into its surface. The scale ranges from '10' to '100'. In the centre of the micrometer is an eyepiece. A screw gauge attached to the graduated circle enables the eyepieces and micrometer to turn on the graduated circle. The engraved scale on the graduated circle ranges from '10' to '360'.

Made: Ross and Company; London, England; 1900 - 1930

: Ross and Company; London, England


Owned: Sydney Observatory; Sydney Observatory
Marks
Text engraved on the micrometer reads 'Ross / London'.
Text engraved on the cross bar of the graduated circle reads 'Dollond London'.
H9987
Production date
1900 - 1930
Height
155 mm
Width
150 mm
Depth
112 mm

 This text content licensed under CC BY-SA.
Acquisition credit line
Source unknown
This object belongs to:
Sydney Observatory Collection
Subjects
+ Astronomy
+ Scientific equipment
+ Sydney Observatory
+ Australian culture
+ Russell, Henry Chamberlain
+ Astronomical telescopes
+ Astronomical equipment
+ Scientific equipment
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{{cite web |url=http://from.ph/259394 |title=Filar telescope micrometer |author=Powerhouse Museum |accessdate=25 July 2014 |publisher=Powerhouse Museum, Australia}}


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