Remarkable contribution made by Parsons family of Birr Castle

Until recently I would have been hard pressed to name a notable feature of Co Offaly. But I now know, after a recent visit, that Co Offaly has a gem of unparalleled value and beauty in the form of the Birr Castle Demesne and Historic Science Centre, testimony to the lives and achievements of the Parsons family over the past 400 in years astronomy, photography, engineering and botany. It is an invaluable national treasure.

In 1620 Sir Laurence Parsons moved to Birr. His elder brother had settled near New Ross and Charles II created the title Earl of Rosse for this family branch which later passed to the heirs of Laurence in Birr. Birr Castle today is home to Lord Rosse (Brendan Parsons), Lady Rosse (Alison Cook-Hurle) and their family.

The two most famous examples of the Parsons' scientific genius are the giant telescope designed and built by the third earl in 1845 and the steam turbine invented by his son, Charles Parsons.

In 1836, William Parsons, third Earl of Rosse, married Mary Field, a Yorkshire heiress with an annual income of £50,000. Parsons used his wife's fortune to fund various projects. He was interested in faint patches of distant light called nebulae whose nature was unknown. Parsons suspected that they were thick clusters of distant stars, but some other astronomers disagreed.

The then largest telescope in the world had a 49-inch mirror but a telescope capable of collecting more light was needed and William Parsons decided to build the world's largest reflecting telescope. Reflecting telescopes use mirrors and large mirrors were then made of an alloy of copper and tin that can be highly polished. The technique of mixing the metals and casting the mirror was a trade secret, so Parsons had to figure it out for himself.

In 1842 he began work on a six-foot mirror and a telescope tube to house it. Four tonnes of metal, taking 26 hours to melt, were needed to make the mirror. Then it had to be cooled slowly for four months in order to prevent cracks, and was carefully polished using a steam-driven grinding machine designed by Parsons himself. Local coopers made the 54-feet telescope tube. The mirror and tube combination weighed 12 tonnes. Thick walls 56 feet high were built to support the telescope.

The telescope was ready in 1845 and made its main discovery that same year. Parsons observed a nebula named M51, which resolved into a spiral shaped cluster of stars. Parson's named it the Whirlpool Nebula and made a sketch of its appearance. This finding was widely publicised and created a sensation. There is good reason to think that the whorls in the sky in Van Gough's famous painting, Starry Night, were inspired by Parsons's drawing. Many other nebulae were also examined by the great telescope and all seemed to be star clusters. The telescope remained the largest in the world until 1917 and astronomers came to Birr from all over the world.

Mary Field did remarkable pioneering work in photography. She experimented with various techniques and processes and in 1859 won the first medal awarded by the Photographic Society of Ireland. Her work was widely exhibited. Her darkroom survives in the castle and is the world's oldest surviving model.

Charles Parsons (1854-1931) was the youngest son of the third earl. In 1884 he invented the steam turbine. For the previous 100 years the industrial revolution had relied on inefficient, slow steam engines that used steam to move crankshafts and pistons and consumed huge amounts of coal.

Parsons's steam turbine used steam very efficiently to directly turn an axle rotor by passing it through a series of increasing sized multi-vaned wheels. It was well-suited for turning the dynamos employed in generating electricity and the new turbine led to global electrification.

Charles Parsons persuaded the Royal Navy to commission two turbine-powered destroyers. The turbine revolutionised marine transport. Enormous liners were now built that would never have been possible using conventional steam engines because of the weight of coal required.

In 1845, when the third earl made his great discovery using the telescope, the Famine arrived in Ireland. To their credit, for the next few years the Parsons family initiated much relief work at Birr Castle, funded out of Mary Field's fortune.

The telescope at Birr remained the largest in the world until 1917, but by this time it had become derelict. It was renovated in the 1990s. A fine historic science centre has also been built at Birr Castle. This contains astronomical instruments, photographs and equipment used by the third earl and his wife and electrical/engineering equipment used by Charles Parsons. A large area also describes the botanical work carried out at Birr.

The giant telescope, the science centre and Birr Castle Gardens are open to the public and attract about 30,000 visitors a year. The gardens are magnificent. A river runs through the demesne, spanned by Europe's oldest wire suspension bridge built about 1820.

The demesne contains more than 1,000 species of trees and shrubs scientifically numbered and catalogued, wonderful formal gardens, the tallest box hedges in the world over 300 years old, a lake, rivers and waterfalls, and more. Covering about 120 acres, the castle gardens are the largest in Ireland and of international botanical significance.

Birr Castle itself is a very imposing and romantic building, but as home to the Parsons family it is not open as such to the public.

William Reville is associate professor of biochemistry and public awareness of science officer at UCC. Go to http://understandingscience.ucc.ie

Last week's column carried the wrong byline. It was written by our regular columnist, William Reville