The Great Telescope of 1900, was the largest refracting telescope ever constructed.

The Great Telescope of 1900, was the largest refracting telescope ever constructed.
In 1892, Francois Deloncle had an idea for the Paris Universal Exhibition of 1900, more commonly known as the World's Fair.

He and his team constructed largest refracting telescope ever made and placed it in the Palais de l'Optique, close the Eiffel Tower.

Because it was built specifically for the Exhibition it was not considered useful for true scientific work.
The telescope had two objective lenses that were interchangeable, and the cast iron frame was set up horizontally. The base was made from seven concrete pillars which had steel towers made to support the twenty-four cylinders in a two hundred foot long tube that boasted a moveable six and one half foot mirror to allow light into the tube. The exhibit was placed in a room that had a retractable ceiling, perfect for star gazing.

The mirrors were made by the Gautier Company and the Jeumont Glassworks in northern France The only lens that was useable was the object lens for photographic Viewing, but the incomplete lens for Visual observing was placed in an optical display in a building near the telescope.

Paul Gautier decided that the seventy-nine-inch diameter mirror would be made entirely by mechanization and was finally completed nine months after the project was started.

The public made fun of the enormous telescope, seeing no value as it was built primarily for the show.

What they did not realize was that the telescope was built on such a large scale to help people understand how similar telescopes worked.

The Chambre des Députés was forced to declare bankruptcy after the telescope was unsuccessfully placed up for auction after the Exposition.

With no serious buyers, the telescope was eventually dismantled, and most of the parts were sold as scrap metal.

The 2-metre (6.6 ft) diameter mirror is On display at the Observatoire de Paris.

Whether or not the lenses and mirror will ever be used again to scan the heavens is doubtful, but they certainly served their purpose of educating and entertaining the public at the Paris Expo in 1900.