Restoration of the Great Telescope (Page 1)

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After the death of the fourth Earl in 1908, the giant telescope fell rapidly into disrepair. The mirror was taken to the Science Museum in London and around 1914, all the metal involved in supporting the telescope was removed and melted down to be used in the First World War. One of the original mirrors is now on exhibition in the Science Museum in London. The second mirror has long since vanished. In 1925 the wooden structures around the walls were demolished for reasons of safety. Between 1996 and 1998, however, a full restoration of the telescope was undertaken, and, as can be seen from the photographs on this page, great care has been taken to recreate the telescope and its supporting structures as closely as possible to the way they appeared 150 years ago.

The 18 metre long telescope tube and speculum box have been restored and there is a system of chains, cranes, weights, windlasses and levers to raise and lower and to move the telescope from side to side, as well as fine movement mechanisms to provide altitude and azimuth measurements. The three movable viewing galleries have been reconstructed and are now fully operational. All moving parts are now hydraulically or electrically controlled.

Although sporadic efforts had been made since 1968 to restore the telescope, it was only after the succession of the present seventh Earl of Rosse that a really serious and determined effort was made to restore the telescope to its former glory. The patronage of various prominent Irish business people, as well as the support of several Irish Government Agencies, in addition to European financial aid, allowed the present Earls vision to become a reality.

Michael Tubridy, Structural Engineer for the project, spent over two years researching and drawing up plans based around information on the telescope drawn from a wide variety of sources, including historical records stored in Birr Castle.

The contemporary photographs of the telescope, taken by Mary, the wife of the Third Earl proved invaluable as a source of reference. In addition, explorations of the site of the original telescope turned up various pieces of equipment used in the operation of the telescope such as counterweights, guide wheels and part of a rack and pinion drive.

Old documents, including ordnance survey maps, observer reports and articles about the telescope written both before and during the operation of the telescope helped define the final specifications of the restored telescope. A model of the telescope, on display in the London Science Museum, also helped in the reconstruction.

The work of restoring the Great Telescope officially commenced on the 22nd of February, 1996. A complete restoration of the East and West supporting walls was completed by June that year. This ensured the structural stability of the two massive masonry walls which provide support to the chains and pulleys required to lift the telescope. It involved removing all vegetation which had taken root in and around the walls, in some cases splitting the original block work. All loose masonry was re-bedded using lime mortar and the top surfaces were racked to ensure rain run-off. Particular care was taken with securing the exact location for re-bedding structural stones required for the fixing of plates and rails for the lifting mechanisms of the telescope. The rare plant life around the restoration site also had to be protected from damage and debris from the restoration process. The blocks of the wall were numbered and replaced where appropriate.

The early months of 1996 also saw the removal of the original telescope tube and the complete clearing out of the floor of the observatory. The original universal joint supporting and allowing appropriate movement of the telescope tube was partially dismantled, load-tested on site and found to be still easily up to its job as main structural support for the tube. The restoration operation may be more accurately described as a recreation of the observatory, as only the supporting walls and the universal joint were actually restored. The new telescope tube used less than 10% of the original timber planking, with all the new planking being attached to a welded steel circular frame. Virtually all the metalwork involved, such as pulleys and counterweights, was fabricated in the workshops of Universal Works.

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Ireland's Historic Science Centre   Birr Co Offaly Ireland