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William Parsons, Lord Rosse

1800–1867

 

William Parsons, third earl of Rosse, is among the giants of nineteenth-century science and one of the most remarkable Irishmen of his day.  Born in York on 17th June 1800, into a leading Irish family, he was a son of Lawrence Parsons, the second early of Rosse.  He was educated at Trinity College, where he became a student in 1818.  In 1821 he went on to Magdalen College in Oxford.  That year he was also elected to Parliament as the member for King's County (now Laois).  He held the seat until 1834, but resigned in order to pursue his scientific interests.  After he inherited his title he was a representative Irish peer at Westminster from 1845.

      He was already deeply interested in astronomy and had made experiments with telescopes at his father's estate at Parsonstown (now Birr).  The key element in a reflective telescope, such as Parsons had in mind, was its mirror.

      William Herschel had already been working with reflecting telescopes, but he had never published any information about how he cast and polished his specula.  Parsons had to make his own experiments.  He described his work in 1828 in the Edinburgh Journal of Science.  His speculum metal combined copper and tin in proportions to make a brilliant alloy.  Because this metal was very brittle, his first mirrors were made up of a number of thin plates of the metal soldered on the back of a strong light framework of a brass composed to have the same expansion rate.  He needed sixteen plates for a three-foot mirror.

      In 1839 the three-foot mirror was finished and mounted, but it presented difficulties due to its expansion, so Parsons decided to cast a solid three-foot mirror.  He achieved this, overcoming yet more technical difficulties, in 1840.  In 1842 he began work on an even larger six-foot mirror, which was finished in 1845.

      This was to be mounted in an instrument which came to be called the Leviathan, and was the largest telescope of the nineteenth century.  If was fifty-four feet long and the tube was so wide that a man could walk upright through it.

      The mirror of Leviathan was seventy-two inches wide.  The instrument took seventeen years to bring to completion.  Using local craftsmen - the sons of tenants on his estate whom he trained as technicians and chemists - he had first to build a steam engine to drive the tools needed to polish the mirror.  Five years were then spent on the composition of the metal alloy for the mirror.  At last he managed to compose an alloy of tin and copper of exceptional brilliance.  His first mirror was three feet wide, but this was followed by a six-foot one which weighed four tons.  This was mounted in the fifty-eight-foot wooden tube.  He let a ball and socket into the solid rock, and on this base laid out a platform of oak trunks over which were laid twenty-seven cast iron plates.  On this machinery the telescope could swing from left to right by a chain drive.  It was protected from the winds by two walls.  It looked for all the world like part of the Gothic castle in which the earl himself lived, surrounded by drawbridges, ladders, and the moving tower in the centre of it all.

      Strange as it appeared, this was not amateurish work.  The sheen which Parsons and his team achieved was created by polishing off a layer 1/10,000 of a millimetre thick from the pre-polished mirror, evenly from the centre to the edge.  This remarkable feat of precision made the mirror almost free of distortion, and was rightly considered an optical marvel.

      The Leviathan established Birr as a leading astronomical site for decades, for this was the largest telescope in existence until 1878.  Rosse and fellow astronomers invited to use the telescope made many extraordinary discoveries.  Parsons himself brought to light the spiral form of nebulae, those strange cloudlike formations in the distant reaches of the universe.  The telescope was powerful enough to reveal many previously unknown features of these mysterious objects.  A special study was undertaken of the nebulae of Orion, and the large drawings which resulted from the observations gave a remarkably clear idea of these objects.

      Though it was eventually stripped down, the telescope itself survives, and its speculum is kept in London at the South Kensington Science Museum.  Rosse's wife was a noted photographic pioneer; his son, the fourth earl (1840-1929) was a noted astronomer, while his third son, Charles Parsons (born in 1854), was the inventor of the steam turbine engine in 1884, which revolutionized shipping and was later applied to airplane jet engines.  Rosse was president of the Royal Society from 1849 to 1854, and chancellor of Dublin University in 1864.

      Though wealthy and indulgent of his scientific interests, Lord Rosse was also a good landlord, especially so during the grim famine years at Parsonstown.  He died at Monkstown on the seacoast south of Dublin on 30th October 1867.

      His great telescope continued to probe the deepest mysteries of the universe from the small town in the Irish midlands.  The discovery of the size and nature of the universe has been one of man's great intellectual adventures, probing as it does into the very first seconds of life itself.  Lord Rosse made his country a part of this great adventure.