Great Paris Exhibition Telescope of 1900

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The Great Paris Exhibition Telescope of 1900 was built as the centrepiece of the Paris Universal Exhibition of 1900. 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.

The Great Telescope, installed, from the ocular lens end.
The Great Telescope, installed, from the ocular lens end.
Plan of the 1900 Paris Exhibition
Plan of the 1900 Paris Exhibition

Contents

[edit] 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 1.25 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)
The telescope: overall side view (top); the siderostat (left) and lens tube (right); ocular lens end (inset)

[edit] Erection of the telescope

The telescope was erected in the Palais de l’Optique on the Champ de Mars, near the Eiffel Tower. 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.[2]

The instrument in place
The instrument in place
The eye-piece holder
The eye-piece holder

[edit] 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. And Eugène Michel Antoniadi (1870-1944) made several drawings of nebulae. 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.[3]

[edit] 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.[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
An 1892 cartoon ridiculing François Deloncle who proposed the project

[edit] 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.

[edit] 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.