Yerkes Observatory, Williams Bay, Wisconsin, USA, 1915.

Photograph of the domes and buildings of the Yerkes Observatory at Williams Bay, Wisconsin in the United States. Its primary instrument is a 40 inch refracting telescope built by the American company of Warner & Swasey Ltd with optics by Alvan Clark & Sons that was completed in 1897. Established as part of the University of Chicago, the observatory was the brainchild of its first director, George Ellery Hale (1868-1938). He managed to convince Charles Tyson Yerkes (1837-1905), a Chicago railway tycoon, to fund the whole project. Today it is still the largest refracting telescope in the world.