Herschel's 40-foot telescope, artwork. Also known as Herschel's Great Telescope, it was designed by the British astronomer William Herschel (1738-1822). The tube was 40 feet (12 metres) long. The first observations with this telescope were carried out on 28 August 1789, and two new mooons of Saturn (Enceladus and Mimas) were discovered. The movement of the telescope was carried out by an assistant in the hut (lower left). Herschel would make his observations from the platform (centre right) at the front of the telescope, looking down the tube at the mirror, which was made of polished metal, instead of glass. The telescope cost 4000 pounds to build, and was dismantled in 1839.