Visitors’ Book of Birr Castle Observatory, 1850-2014 (L/6/2) Spread 0

Visitors’ Book of Birr Castle Observatory, 1850-2014 (L/6/2) Spread 0 cover

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William Parsons, 3rd Earl of Rosse (1800-1867) served as President of the Royal Society in the years 1848-1854. His main scientific interests were in astronomy. Rosse revolutionised deep space observation by constructing what was, in the 1840s and for many years after, the largest reflecting telescope in the world – the ‘Leviathan’ of Parsonstown. This instrument was built by local craftsmen at the Earl’s seat of Birr Castle in County Offaly, Ireland. Although Rosse had used telescopes at the site since the 1820s, the Leviathan possessed massively enhanced light-gathering capability. It employed a 72-inch aperture and speculum mirror in a tube of over 50 feet in length – the whole telescope demanded its own supporting walls and mechanism for orientation.

Both in terms of its impressive engineering and optical capabilities, the Parsonstown instrument attracted professional scientists and sightseers in equal measure. Rosse employed observatory staff for regular periods of research, notably William Rambaut and George Johnston Stoney, but other professional astronomers are known to have used the telescope during short stays. The main scientific question that the telescope was intended to resolve lay in determining the nature of nebulae. These faint and diffuse areas of starlight had fascinated professionals since sweeps conducted by William Herschel (1738-1822) and his sister Caroline (1750-1848) had enumerated them. William’s son Sir John Herschel (1792-1871) continued the business of cataloguing such objects but it was not until Rosse’s telescope was built that there seemed any hope of discovering the varied nature of these objects, some of which we now know to be other galaxies.

The visitors’ book records casual use of the Leviathan in addition to those who simply came to Birr Castle to wonder at it. The book commences on 9 September 1850 with the signature of the mathematician and computer pioneer Charles Babbage (1791-1871). Babbage’s name – synonymous with technological innovation in support of mathematical and astronomical data, the purpose for which his calculating engines were originally developed – was surely a deliberate choice on behalf of the Earl of Rosse, emphasising the nature of Birr Castle Observatory’s work to all future signatories.