Herschel's 20-foot telescope, artwork. This telescope was designed by the British astronomer William Herschel (1738-1822). The tube was 20 feet (6 metres) long. It was easier to use than his larger 40-foot telescope of 1789, but operated in a similar way. An assistant would use the levers (lower right) to move the telescope. Herschel would make his observations from the platform (centre left) 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 thousands of pounds to build. With this telescope, Herschel discovered two new satellites of Uranus, later named Titania and Oberon.