The 'Thorrowgood Telescope' was built by T. Cooke & Sons of York & London in 1864, as recorded by the small embossed plate at the top of the pillar. The achromatic doublet object glass has an aperture of 8 inches and a focal length of 114 inches (f/14), and is of excellent quality. The mounting is an example of the 'German' form of equatorial mounting, named after Wilhelm Struve's telescope, the 'Great Dorpat Refractor' of 9.5 inches aperture (1824). Many large refracting telescopes have used this form of mounting, including the Lick 36-inch and Yerkes 40-inch telescopes. The entire sky is accessible to a telescope on this type of mounting. When an object is in the eastern sky it is most convenient to have the tube of the telescope on the west side of the pillar, and for an object in the western sky the tube should be to the east. When an object crosses the meridian between the zenith and the pole, it is usually necessary to interrupt the observations to reverse the position of the telescope tube. This problem does not arise with an 'English' mounting, such as the Northumberland telescope. As on the Northumberland, the sidereal drive is now provided by a small electric motor, but here most of the original mechanical driving clock can still be seen on the North side of the pillar.
The history of this telescope is known in considerable detail. The first owner was Rev. William Rutter Dawes, described as 'eagle-eyed' when he was presented with the Gold Medal of the Royal Astronomical Society for his work on the measurement of double stars (1855), most of which had been done with telescopes made by the American optician Alvan Clark. Dawes started to use this telescope on 1865 April 13, but died in 1868 on February 15. He was qualified in medicine before taking Holy Orders, and in his obituary it is recorded that he ''was ever ready to impart gratuitous advice to the sick'' - a form of generosity more liable to misunderstanding now than then. In 1867 an attempt to buy the telescope for the Observatories was made by J. C. Adams. He argued that it was of superlative quality, superior to the 9.5-inch at Dorpat and to Herschel's 18-inch reflector at the Cape. Dawes had asked only 580 pounds but after four months the Observatory Syndicate withdrew its provisional approval.
George Hunt (1823 - 1896) bought the telescope in 1869. His father and uncles wished him to become a member of their business, but after eighteen months' trial he found it so distasteful and the loss of time for his literary studies so trying that he determined to give up business. After his father's death, he spent most of his time with an uncle, who eventually made him his heir. It is not known how much use he made of the telescope, but he published only one paper, "On the Identity of the Triple Star H I."
The first long fruitful period in the history of the telescope was in the ownership of William Henry Maw (1838 - 1924). Left an orphan at 16, Maw studied engineering and became an excellent draughtsman. Employed by the Eastern Counties Railway, he became head of the drawing office, aged 21. In 1865 he left the then Great Eastern Railway to join in the founding of the technical journal Engineering, of which he was an editor until his death. He was a founder member of the British Astronomical Association in 1890, at a time when the Royal Astronomical Society refused Fellowships to ladies, and became Treasurer for many years and President for a standard term of two years. Maw erected this telescope at his house at Outwood, Surrey, in 1896, and used it for measurements of double stars.
The telescope was offered for sale in 1927 by C. Baker of 244 High Holborn, London, at a price of 500 pounds. An advertisement published in the Journal of the British Astronomical Association listed the extensive range of accessories, including 10 astronomical eyepieces, which we still have.
William John Thorrowgood (1862 - 1928) was the last private owner of this telescope. He had spent his professional life in the service of the Southern Railway. After his retirement in 1927 he installed the telescope at Wimbledon, but had little time to enjoy it. He bequeathed it to the Royal Astronomical Society, which, having no suitable place to erect it or to store it, offered it to Professor Eddington, Director of the then University Observatory, initially for a period of 10 years. It was erected on its present site early in 1929. An engraved brass plate, made recently in our Workshops, serves to remind us that the telescope is here on extended loan.
The telescope is now used by members of the University Astronomical Society and is also available on Public Observing Nights. Double star measurements are currently being made by Mr. R.W. Argyle of the Institute of Astronomy.