1-158-700 - Oxford Science Archive/Heritage Images

William Herschel's reflecting telescope of 40 ft (12 m) focal length, 1789 (1807). Built by the German-born English astronomer, William Herschel (1738-1822), in the grounds of his home in Slough, Berkshire, this instrument was the largest in the world, with a 4 ft (1.2 m) mirror. Herschel made observations with this telescope, including the discovery of two new moons of Saturn on the first night he used it, but made more use of a smaller 18 inch/46 cm instrument. From The Edinburgh Encyclopaedia. (Edinburgh, 1807-1829).