Somewhere inside the historic building of the Paris Observatory, on the banks of the Seine, is stored packed in boxes, some of the biggest lenses ever made by man. Two of them have a dimension of 1.25 m in diameter. These lenses were the most important components of the largest refractor telescope ever created.
Construction of the telescope for the Great Paris Exhibition began in 1892, a few months after the French government announced plans for the 1900 World Exhibition in Paris. The idea was to build an unusual telescope in the likeness of the Eiffel Tower, built as the entrance to the World’s Fair in 1889. These fairs, which are held periodically throughout Europe, thanks to the host country, as well as the participants were given the opportunity to demonstrate achievements in industry, science, and technology. Countries competed for prestige, demonstrating their latest machines and products, cultural achievements and imperial ambitions.
Total World Exhibition was successfully completed three years ago, in 1889, in France. And then came the news that Germany plans to host an international fair in 1896, or possibly 1900. News threatened the prestige of France, because at that time believed that the country, where the exhibition will determine the philosophy of the early XX century. The French government has decided to act quickly and announced the holding of the exhibition in 1900, to seize the initiative from Germany.
The centerpiece of the exhibition was devoted to the big telescope, placed in the Palace Optique. Telescope for visual observation and for the manufacture of photographic plates had two interchangeable lenses the size of 1.25 meters in diameter. They have been the focal length of 57 meters, and the tube where they were located, had a length of 60 meters. Because of their huge size and weight, the telescope could not move and aim at celestial objects. Instead, it was installed in a fixed horizontal position, and the image of astronomical objects has been forwarded to the optical tube through a movable mirror system, known as Foucault siderostat. The eyepiece of the telescope was mounted on rails and can be shifted by 1.5 meters to focus.
Engraving of a large telescope at the 1900 World Exhibition in Paris shows a general view (top); Siderostat (left) and the tube (left); and ocular lens end (box)
Telescope demonstrated at the show for about a year, during which only a few scientific observations were made. Astronomers have observed sunspots and nebulae, and made great photos of the lunar surface, in spite of the fact that the location of the telescope at the Fairgrounds near the powerful and bright lights are not suitable for astronomical observations. Eventually, the telescope appeared in many advertising course, not serious astronomical tool. During the fair, thousands of people came to look through the telescope. They paid a few francs, and looked through the eyepiece.
The company, which was established in 1886 to build a telescope, went bankrupt, and the telescope was put up for auction in 1909. So far no one has bought. Eventually, the telescope was disassembled for scrap, and the lenses and mirrors deposited at Paris Observatory, where they still are, and.
Although the telescope was completely useless for science, but as a central showpiece latest advances in industry and technology, he did serve some purpose.
Today, almost all large optical telescopes used for astronomical purposes, are mirror telescopes, because the mirror telescopes are not limited in size and have no technological restrictions as refracting telescopes. The biggest acting refractory telescope is in Yerkes Observatory, and it uses 102 cm refractor, which is 23 centimeters lower than the telescope on the Grand Paris Exposition.