1-152-588 - Ann Ronan Picture Library/Heritage-Images

William Herschel's reflecting telescope with focal length of 40 feet, Slough, England, 1809. The illustration shows the top of the brick foundation and the wheeled platform on which the instrument was mounted. The telescope was constructed by Herschel (1738-1822) in the grounds of his home at Slough, and completed in 1789. On the night of 28 August that year, the first time he had used the telescope, Herschel discovered two new moons of the planet Saturn.