Herschel's 10-foot telescope, artwork. This telescope was designed by the German-born British astronomer William Herschel (1738-1822). The tube was 10 feet (3 metres) long, but was smaller than the larger 20-foot and 40-foot models. It is mounted on a wheeled frame so that it can be moved to point in the right direction, and various mechanisms allow the angle to be adjusted as needed. The observer would use a ladder to make observations by looking down an eyepiece on the side of the tube (upper left) at an image that was projected to the side by the primary mirror in the bottom of the tube. The mirror was made of polished metal, instead of glass. This was one of more than 400 telescopes designed and built by Herschel, whose discoveries included Uranus (1781) and several moons of Saturn and Uranus.