uring the eighteenth century, few people had a greater impact on astronomy than William Herschel (1738-1822). At a time when astronomers were preoccupied with measuring the position of stars to ever greater levels of precision, he was busy exploring the structure of the universe. He was also active in advancing telescope technology. Herschel's serious interest in astronomy did not develop until 1773, long after he had moved to England to escape the French occupation of his native Hanover. As a professional musician and composer, he had gained the post of Director of Music for Bath. In his spare time he developed his interest in astronomy and having found commercial telescopes unsatisfactory he learnt how to make his own.

Herschel built his telescopes to a design first suggested by Isaac Newton, which used mirrors rather than lenses to focus light. With time he perfected his instruments until they were superior to any others then available. This led to his discovery of Uranus in 1781 with a telescope similar to the one shown here. The discovery made Herschel famous overnight, as no new planets had been observed since antiquity. He originally named the planet 'Georgium Sidus' (George's Star) after reigning King George III, but fellow astronomers did not agree with his choice. In 1782, Herschel was appointed 'Royal Astronomer'. This royal patronage allowed him to give up his musical duties and move to Datchet near Windsor where he could devote himself fully to astronomy.

Using the experience that he had gained with his smaller telescopes Herschel was able to construct two smaller instruments with a focal length of twenty feet. One was built while he was still living in Bath, but it proved difficult to use due to the size of his garden. With his new instrument Herschel embarked on a systematic survey of the heavens. This was to be the most productive period of his life. He was able to confirm his earlier observations whilst making new discoveries. He was also able to uncover many more double stars, some of which he proved were rotating around each other.

There had been a long debate during the eighteenth century as to why these stars appeared double. Some astronomers thought they were simply 'a line of sight effect' and that the stars lay in the same direction but were at different distances. Herschel's observations over many years proved that some moved in orbit around each other.

These successes spurred Herschel to build an even larger telescope and, with patronage from the King, he was able to cast, polish and grind several speculum mirrors of forty-eight inches in diameter. The resulting forty-foot telescope was erected in Herschel's new home in Slough in 1789 where it became an instant landmark, due to its sheer size. During its construction the King was a frequent visitor and delighted in conducting people through the enormous telescope tube. On one occasion whilst with the Archbishop of Canterbury, the King was heard to say, 'Come, my Lord Bishop, I will show you the way to heaven!' Alas, the telescope was not as successful as hoped, and was little used. This was largely due to its huge bulk which took three to four people to operate. The instrument fell into disuse in 1815 and was finally dismantled in 1839.