Yerkes Observatory, in Williams Bay, Wisconsin, houses the largest refracting telescope ever built for astronomical research, with a main lens that's 40 inches (1.02 meters) in diameter.

The original instrument to occupy the 25-foot diameter dome was the 10.5-inch Bausch refracting telescope (f/15.5) installed in the brand new observatory in 1953.

It was a memorial to her late husband, Dr. Edward P. Burrell. The observatory houses a Warner & Swasey refracting telescope with a 13 3/8-inch objective, a 4½-inch finder and a 1-inch finder.