William Parsons, 3rd Earl of Rosse

William Parsons, 3rd Earl of Rosse PRS, had a rich and illustrious career, but he is perhaps best known for his contributions to astronomy. Educated at Trinity College Dublin and Madgalene College, Oxford, where he graduated with first class honours in Mathematics in 1822. He lived in his family’s estate at Birr Castle, Parsonstown, King’s County – today Birr in County Offaly. He had a great interest in the natural world, and his enthusiasm for astronomy and engineering passed down to two of his sons.  

Lawrence Parsons, 4th Earl of Rosse, followed his father’s footsteps and focused on astronomy, while his brother, the Honourable Sir Charles Algernon Parsons, was primarily an engineer and invented the modern steam turbine in 1884, allowing for cheap electricity which revolutionised power generation on land and sea. He founded ‘C. A. Parsons and Company’ in Newcastle upon Tyne, which is today a part of Siemens Energy. His engineering interests also extended to astronomy: he acquired the famous Grubb Telescope Company in 1925 and renamed it into Grubb Parsons (or, in full: ‘Sir Howard Grubb, Parsons and Co. Ltd.’) – for more on that see the section on Thomas and Howard Grubb. 

3rd Earl of Rosse designed, built, and used a number of telescopes along with his wife, the Rt Hon. Mary Parsons (née Field), who was also an accomplished blacksmith and a pioneering photographer. Starting with smaller structures and finding telescope-making a closely-guarded secret those in the know were unwilling to divulge, they had to invent many of their own techniques. Constructed between 1842–45, the work culminated in what was to be, at 72 inch (6 ft; 1.83 m), the largest telescope by aperture size for 72 years: The Leviathan of Parsonstown. It was a marvel of Victorian engineering, with the metal mirror alone weighing about 12 tons, and the tube 52 ft (15.85 m) in length. Experts helped with its construction, including the renowned telescope-maker Thomas Grubb and the Director of Armagh Observatory Thomas Romney Robinson, who made notes on the casting of the mirror: 

“On this occasion, besides the engrossing importance of the operation, its singular and sublime beauty can never be forgotten by those who were so fortunate as to be present. Above, the sky, crowded with stars and illuminated by a most brilliant moon, seemed to look down auspiciously on their work. Below, the furnesses poured out huge columns of nearly monochromatic yellow flame, and ignited crucibles, during their passage through the air, were fountains of red light, producing on the towers of the castle and foliage of the trees, such accidents of colour and shade as might almost transport fantasy to the planets of a contrasted double star.” 

Leviathan of Parsonstown photographed in 1885

Director Robinson was present at the first viewing with the telescope. He was a frequent visitor to Birr Castle and helped Lord Rosse interpret his observations. One of the first of these was of M51, also called the Whirlpool Galaxy. Lord Rosse made a detailed sketch of its spiral structure, which closely resembles modern photographs. He theorised that ‘nebulae’ like this were composed not of dust but of many stars – a view which Sir John Herschel, one of the leading astronomers of the era, opposed. It is perhaps poetic, then, that the Leviathan of Parsonstown was only superseded by the 100-inch Hooker Telescope on Mt Wilson, California, in 1917 – the instrument Edwin Hubble used to show that such nebulae are indeed their own galaxies, full of stars. Dr J. L. E. Dreyer from Denmark, the Director of Armagh Observatory after Robinson, began his Irish astronomy career as the assistant at Birr Castle to Lawrence Parsons, 4th Earl of Rosse. 

Lord Rosse’s sketch of M51 (Whirlpool Nebula) around 1845