The historic 24 inch diameter Clark refractor telescope was used by Percival Lowell at the turn of the century to make his famous observations and drawings of the planet Mars from Lowell Observatory in Flagstaff, Arizona. It was the last of the large refractors made by the optical firm Alvan Clarke and Sons of Cambridgeport, Massachusetts. It weighs 13 tons and has a focal length of about 30 feet.