William Herschel's 40 foot telescope at Slough, Berkshire, 1795

William Herschel's 40 foot telescope at Slough, Berkshire, 1795. Engraved plate taken from 'Philosophical Transactions', showing the famous astronomer, Sir William Herschel's (1738-1822) 40 foot telescope. This reflecting telescope used a concave metal mirror 48-inch in diameter that weighed nearly a tonne. The massive tube was slung from block and tackle carried by a framework of lashed wooden spars. Several workmen were required to move and aim the telescope. As royal astronomer, Herschel managed to obtain patronage from King George III to build the telescope. It was finally completed in 1787 at a cost of over £4000. The telescope quickly became a landmark of Slough, visited by the rich and famous whene they visited the king at nearby Windsor Castle. ©SSPL/Science Museum