Ritchey Mirror Grinding Machine

George Willis Ritchey built this mirror grinding machine at the Yerkes Observatory in Williams Bay, Wisconsin, in the late 1890s. Under the sponsorship of George Ellery Hale, the machine was used to grind a series of telescope mirrors starting with a 60-inch mirror for a telescope initially intended for the Yerkes Observatory. The grinding machine was moved to Pasadena in 1904 to complete work on the 60-inch mirror. At some later time the apparatus was transferred to the California Institute of Technology. The Institute then sold the machine to the Lick Observatory of the University of California in 1949. The machine was used for making numerous mirrors over the next four decades and extensively modified over that period. It embodies the "sub-diameter tool" design approach to making large telescope mirrors whereby the grinding tool is drawn across the mirror blank by programmable rotating arms. It was donated to NASM by the Lick Observatory in 1993 and shipped in March of that year.