English: Model of Telescope with which William Herschel discovered Uranus. In the Herschel Museum of Astronomy in Bath. The secret of Herschel's success as an observer was the power and magnification of his telescopes. This seven foot long, six inch diameter, ƒ14 reflector was particularly favoured. Its main mirror at the bottom of the tube and the secondary mirror near the top in front of the ocular were made of speculum metal. It was with a seven foot telescope that Herschel made the discovery of the planet Uranus in 1781