Refracting telescope, 1870-80.
© Science Museum / Science & Society Picture Library
This telescope was made by the American instrument maker Alvan Clark of Cambridge, Masachusetts, United States. The telescope has a 4-inch aperture lens and a tapering mahogany tube. To aid the location of objects under study, the telescope is provided with a smaller finder telescope. It is carried on the earliest surviving example of an equatorial mounting made by this telescope maker. Prior to the emergence of Alvan Clarke, most telescopes sold in America were imported from Europe. Later in the 19th century, the Clarke Company produced some of the world's largest optics for refracting telescopes, including a 40-inch lens which they supplied to the Yerkes Observatory in Wisconsin in 1895.