Yerkes 40' telescope

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In 1890, this massive telescope was already taking shape, destined to claim the title of world's largest ever constructed. It achieved its goal in 1897 when it officially opened for business and held onto the record until 1909. The telescope remains the undisputed champion of refractors even today. Its lenses originated as glass disks expertly cast by Mantois of Paris, who then handed them over to Alvan Clark and Sons in Cambridgeport, Massachusetts to be polished into 40-inch behemoths. Meanwhile, Warner and Swasey of Cleveland took charge of building the telescope's mounting system and a colossal dome that stretched an impressive 90 feet in diameter. They also designed and constructed a movable floor measuring 75 feet across, which allows astronomers to rise up to the eyepiece of the telescope. This ingenious feature is crucial because the telescope pivots around its central axis: if one end is trained on a star hovering low on the horizon, the other end will be way off the ground. To rectify this situation, the floor rises to elevate the astronomer to the eyepiece level.