The refracting telescope on Mt. Hamilton was Earth's largest refracting telescope during the period from when it saw first light on January 3, 1888, until the construction of Yerkes Observatory in 1897. Warner & Swasey designed and built the telescope mounting, with the lens manufactured by one of the Clark sons, Alvan Graham. E. E. Barnard used the telescope in 1892 to discover a fifth moon of Jupiter, Amalthea. This was the first addition to Jupiter's known moons since Galileo observed the planet through his parchment tube and spectacle lens. The telescope provided spectra for W. W. Campbell's work on the radial velocities of stars.