The Great Paris Exhibition Telescope of 1900 was built as the centrepiece of the Paris Universal Exhibition of 1900. The Exposition Universelle of 1900 was a World's fair held in Paris, France, to celebrate the achievements of the past century and to accelerate The largest refracting telescope built to that time, it was instigated in 1892 by François Deloncle (1856-1922), a member of the French Chambre des Députés. A refracting or refractor telescope is a dioptric Telescope that uses a lens as its objective to form an image Year 1892 ( MDCCCXCII) was a Leap year starting on Friday (link will display the full calendar of the Gregorian Calendar (or a Leap year Chamber of Deputies (la Chambre des députés was the name given to several parliamentary bodies in France in the nineteenth and twentieth centuries 1814–1848

The Great Telescope, installed, from the ocular lens end.

Plan of the 1900 Paris Exhibition

Construction of the telescope

The instrument was to be 60 meters long. The reflecting mirror was 2 meters in diameter, and the two objective lenses were 1. A lens is an optical device with perfect or approximate Axial symmetry which transmits and refracts Light, converging or diverging 25 meters in diameter. It was designed to reflect celestial light through the tube (and end lenses) and to project them onto a large screen. The mirror was ground mechanically by the Gautier Company (headed by Paul Gautier, 1842-1909) and took nine months to finish. The blank for the mirror was cast by Georges Despret, director of the Jeumont glassworks in Northern France. The lens blanks were cast by Édouard Mantois (1848-1900) and ground by Gautier. ^[1] By the time the Paris Exhibition opened only the object lens for photographic observation was ready. The visual object lens, unfinished, was put on display nearby.

The telescope: overall side view (top); the siderostat (left) and lens tube (right); ocular lens end (inset)

Erection of the telescope

The telescope was erected in the Palais de l’Optique on the Champ de Mars, near the Eiffel Tower. The Champ de Mars (ʃɑ̃ də maʁs is a large public green-space in Paris, France, located in the 7th ''arrondissement'', between the Eiffel The Eiffel Tower (Tour Eiffel /tuʀ ɛfɛl/ is an Iron Tower built The tube, oriented north-south, was made up of 24 cylinders 1. 5 meters in diameter and rested on 7 concrete and steel pillars; its axis was 7 meters above the floor. The room at the end which housed siderostat with the mirror had a movable dome to allow direct access to the sky. A Heliostat (from Helios, the Greek word for sun, and stat, as in stationary is a device that tracks the movement of the Sun. ^[2]

The instrument in place

The eye-piece holder

Scientific observations

A few scientific observations were made using the giant telescope, even though it was not designed for scientific use. Théophile Moreux (1867-1954) observed sunspots through the telescope and made drawings of them. Theophile Moreux (1867 &ndash July 13, 1954) was a French Astronomer and Meteorologist. A sunspot is a region on the Sun 's surface ( Photosphere) that is marked by intense magnetic activity which inhibits Convection, forming And Eugène Michel Antoniadi (1870-1944) made several drawings of nebulae. A nebula (from Latin: "mist" pl nebulae or nebulæ, with ligature or nebulas) is an Interstellar cloud of As well several large photographs of the surface of the moon, made by Charles Le Morvan (1865-1933), were published in the Strand Magazine, November 1900. The Strand Magazine was a monthly fiction magazine founded by George Newnes. ^[3]

Aftermath

After the company, organized in 1886 to build the telescope, went bankrupt the telescope was put up for auction (1909). No buyer was found and eventually the components were scrapped. The 2-meter diameter mirror is on display at the Observatoire de Paris, and two of the lenses have recently been discovered in packing crates in the basement. The Paris Observatory (in French Observatoire de Paris or Observatoire de Paris-Meudon) is the foremost astronomical observatory of France, ^[4]

Throughout its existence the telescope was the butt of many derisive jokes and unflattering cartoons. In part this was due to the belief of the academic community that the telescope would be completely useless. But as the centrepiece of an exhibition showcasing the best of the recent advances in industry and technology it served its purpose. ^[5]

An 1892 cartoon ridiculing François Deloncle who proposed the project

Bibliography

• Paul Gautier, “Note sur le sidérostat à lunette de 60 m de foyer et de 1,25 m d’ouverture,” in Annuaire du Bureau des Longitudes pour 1899 (Paris, 1898), pp. C1-C26.
• Françoise Launay, “The Great Paris Exhibition Telescope of 1900”, Journal for the History of Astronomy, 38 (2007), 459-475.

References

1. ^ Launay, pp. 463-466.
2. ^ Launay, pp. 467-468.
3. ^ Launay, pp. 471-473.
4. ^ Launay, p. 468-471.
5. ^ Launay, p. 461-2.