The largest practical lens size in a refracting telescope is around . The objective in a refracting telescope refracts or bends light. Mr. Hugh Pattinson loaned his refracting telescope of . From these experiments Newton concluded that no improvement could be made in the refracting telescope. The observatory is equipped with a large refracting telescope made by John Brashear. This telescope was the largest refracting telescope at that time. It was the largest refracting telescope used for astronomical research. In 1791 he completed the Shuckburgh telescope, an equatorial mounted refracting telescope. A Troughton refracting telescope of 2.5 inch aperture was installed in a dome in 1795. Galileo Galilei's discovered the Galilean satellites of Jupiter in 1610 with a refracting telescope. The main observatory building offers free 15-minute guided tours of the Great Lick refracting telescope. In 1857 a refracting telescope of aperture objective, the Arago equatorial telescope, was completed.