Yerkes Observatory, astronomical observatory located in Williams Bay, Wis., on the shore of Lake Geneva. It was founded in 1892 with funds provided by Charles T. Yerkes and its first director was George E. Hale. The observatory is administered by the Univ. of Chicago. The principal instrument is a 40-in. refracting telescope, completed in 1897, the largest of its type in the world; its size is very near the practical limit for a refractor because of distortions caused by the weight of the lens itself. Other equipment includes a 41-in. and two 24-in. reflecting telescopes and a number of specialized instruments. Principal programs include astrometry, and studies of comets, galaxies, and the interstellar medium.