Yerkes 40' telescope

In 1890, this telescope was already partially under construction, and it was planned to be the world's largest telescope. It was, in fact, the world's largest telescope from 1897 (when it was commissioned) to 1909, and it is still the world's largest refractor. The lenses started as glass disks cast by Mantois of Paris and were polished into 40-inch lenses by Alvan Clark and Sons in Cambridgeport, Massachusetts. Warner and Swasey of Cleveland built the mounting for the telescope and a 90-foot di