Herschel's 40-foot telescope, computer artwork. Designed by the British astronomer William Herschel (1738-1822), this telescope with a tube 40 foot (12 metres long) was located at Observatory House in Slough, England. Observations began on 28 August 1789, and two new moons of Saturn (Enceladus and Mimas) were discovered. The telescope was moved by an assistant in the hut (lower left). Herschel would make his observations from the platform (lower right) at the front of the telescope, looking down the tube at the mirror, which was made of polished metal, not glass. The telescope cost 4000 pounds to build, and was dismantled in 1839.