Tuesday 4 July 2017

The World’s Largest Telescope

Anyone attending the Great Industrial Exhibition in London in 1862 could have been forgiven for passing by the sight of two circular blocks of glass, 26 inches in diameter and two inches thick, standing on their edges being displayed by Messrs Chance of Birmingham. Impressive though they were these optical glasses could easily be missed alongside the great machines - such as Charles Babbage’s analytical engine, cotton mills, maritime engines, and London and North Western’s passenger locomotive, Lady of the Lake - being displayed by the 28,000 exhibitors from 36 countries.

However, there was one visitor to the event who saw the opportunity to create a lasting legacy. Robert Stirling Newall of Gateshead, whose fortune was made from the manufacture of wire rope,  purchased the glasses for £500 pounds each. They were the largest in the world at the time, being nearly twice the diameter of the previous largest, and Newall’s intention was that they would be the foundation of a telescope that would exceed in size all that had gone before.

The project would thrust England, and York in particular, to the forefront of the optical arts, ‘as we were in Dolland’s time’ according to the journal Nature. Contemporary commentators believed the optical art had been stifled in England by an ill-advised duty on glass, and for many years England had been dependent on foreign built telescopes, mainly from France and Germany. At the time of the Great Industrial Exhibition the telescopes with the largest object glasses in England - at Greenwich, Oxford and Cambridge - were all of foreign make. Newall, however, opted to use T. Cooke and Sons of York for his grand project.

Cooke had been at the forefront of resurrecting the art of optical manufacture in England. Samuel Smiles in Men of Invention and Industry relates that Cooke made his first object glass from the base of a glass tumbler, and from this unlikely beginning set up T. Cooke & Sons in 1837. Based at No. 50 Stonegate, York, he specialised in making telescopes and other optical instruments, such as surveying equipment, microscopes, turret clocks and later steam engines (for an unsuccessful steam carriage or motor car). He gained a reputation for excellence, and in 1860 constructed a 5.25 inch telescope for HRH the Prince Consort that was erected at Osborne House, and also provided Sir Norman Lockyer a telescope for his Wimbledon Observatory in 1861. In 1862 he exhibited his creations at the Great Industrial Exhibition in London, bringing home two First Class Medals, one for the excellence of the object glasses and mountings of his telescopes, the other for the construction and finish of his turret clock, and it was here that he came into contact with Mr Newall.

Newall sought quotes from both Cooke and Thomas Grubb of Dublin, but Cooke was so eager for the contract that he bid too low and underestimated how long it would take to construct. The project took far longer than the year he had anticipated. Newall became increasingly frustrated throughout the endeavour, whereas Cooke frequently sought advances to cover his costs. The project nearly caused the demise of Cooke’s business which was still suffering financial difficulties as a result several years after the completion of the telescope; Sir Norman Lockyer writing in 1878 stated, ‘Cooke did not hesitate to risk thousands of pounds in one great experiment, the success of which will have a most important bearing upon the astronomy of the future’.

The general design was the same as Cooke’s equatorials  but the huge size necessitated special arrangements. The main issue was the crafting of the glass lenses. Special equipment had to be designed to handle the discs, and the lenses had to be floated in mercury to prevent them breaking under their own weight. Lockyer stated that it took 1560 hours to grind the discs to the required shape, the thickness being reduced by an inch in the process. The work took place at Cooke’s Buckingham Works, Duke’s Hall, in the Bishophill area of York, but the scale of the project required the final assembly take place in the open near the city wall; Employee Mr Graham recalled the telescope “…..was a big undertaking and it had to be erected on the moat, near the City walls about the place where Newton Terrace now stands.”. It was 1870, and the telescope had taken around six years to complete. Once assembled it was taken to Newall’s observatory at Ferndene, Gateshead, and it was not until 1871 that it was fully installed in the observatory.

The resulting instrument weighed 9 tons and was 32 feet in length. At a time when the largest lenses in Greenwich, Oxford, and Cambridge were 15. 5 inches, the largest in Russia at Pulkova were 15 inches, and the largest in the U.S. were 18.5 inches, the step forward in manufacturing techniques required to produce a telescope with 25 inch discs, weighing 144lb, was considerable. The telescope was nearly twice as powerful as the 18 inch Chicago instrument, having a 485 inch area compared to 268, and had a focal length of 29 feet. The diameter of the object end was 29 inches, the diameter of the tube centre 34 inches, the diameter of the eye end 22 inches, and the support pillar was 19 feet high.

The tube was cigar shaped and made of steel plates riveted together in 5 sections. Inside there were five other tubes of zinc increasing in diameter from eye end to object end. The wide end of each tube overlapped the narrow end of the next with an inch of space left around the end of each to aid ventilation and prevent currents of warm air interfering with the light. The ends were lighter than the centre to prevent them destabilising the telescope.

Fixed above and below the eye end of the tube were two finders, each of 4 inches aperture, 12.5 inches in area, to aid accessibility. An additional telescope with an object glass of 6.5 inches was fixed between the two finders to assist the observation of objects (such as comets) for which the main telescope was not suited.

The observatory housing the instrument was between 40 and 50 feet in diameter and packed with apparatus to allow the telescope to be easily maneuvered, the temperature always the same inside and out to prevent currents of air interfering with observations. However, the atmosphere in England was ‘not the best suited for such an instrument’ and as early as 1870 the journal Nature was reporting that Mr Newall intended to move the instrument after preliminary testing to a location more suited to astronomical observation. This was taken to mean that it would not remain in England ‘every increase in the size of the object-glass or mirror increases the perturbating effects of the atmosphere, so that the larger the telescope, the purer must be the air’. However this was not to be the case, and Mr Marth, known for his work with the Lassel Reflector at Malta, was given charge of the instrument in Ferndene.

Newall’s telescope drew widespread attention, the US government sent Commodore BF Sands of the US Naval Observatory with a deputation of astronomers to examine it and this resulted in a commission of a telescope that would be one inch larger. Austria ordered one the same size.
Cooke never got to see the result of his work as he died in October 1868, whilst Newall was only able to claim to be the owner of the world’s largest refracting telescope for a short period, being overshadowed by the 26 inch Washington Naval Observatory telescope in 1873. However, the telescope was of such exceptional quality that it was used for years to come. On Newall’s death in 1889 it was moved from Gateshead to Cambridge University Observatory and by 1925 it was in the charge of Prof James Newall, Mr Newall’s son, director of the Polar/Solar Physics Observatory, Cambridge. There it stayed until the 1950’s when it was donated to the Greek National Observatory, Mt Penteli, Athens, where it can still be found today having undergone a complete restoration in 2013.

T. Cooke and Sons continued to produce telescopes and exported all over the world, eventually merging with Troughton and Simms in 1922, and Vickers Instruments in 1963. The records of the company can be found at the Borthwick Institute for Archives as part of the Vickers Instruments archive. An online catalogue for the archives of Vickers, Cooke, and Troughton and Simms can be viewed on Borthcat.

Further information:

A full technical description of the telescope can be found in Stargazing, past and present, by Joseph Lockyer.

Graham Hughes,
Archives Assistant.

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