It is a twin refracting telescope built in 1891, with one visual and one photographic, on a single square-tube together on an equatorial mount, inside a dome.

[1] The telescope is noted for being used to disprove the theory of Martian canals, which was a popular story in the late 19th century.

[1][3] In this period the observatories were not just a telescope, but more like a laboratory, with integrated equipment, libraries, and workshops for practical and theoretical astronomy.

[2] Janssen was famous for his role in the discovery of Helium in 1868, and by 1875 he was authorized to build a large astrophysical observatory.

[4] The facilities were built on the ruins of an old French palace, noted in the publication Scientific American for "beautiful view of Paris and the river seine.

"[5] As one era ended a new one started, with the foundations of the telescopes built on the ruins, and old stables converted into laboratories.

[6] The usuefull location meant the sites involvement in the activities of that war, and by the end it was left ruin.

[12] The observatory resides in a special park designed by fr:Urbain Vitry, the Parc de l'Observatoire.

[15] A trifecta of observational factors synergize; viewing through the third largest refractor in the World, Mars was at opposition, and exceptional clear weather.

[18] This idea also crumbled, as larger telescopes being used by experienced astronomers under the best conditions available were not seeing any canals, but rather finer details of the Martian surface and atmosphere.

[18] In addition, a telescope at Pic Du Midi was used to take over 1300 pictures of Mars, and among them "no trace" of canals could be seen.

[19] In the early 20th century, the Meudon refractor was noted for being very steady, and this aided in taking micrometer measurements of the Galilean moons of Jupiter.

[14] In 1954, a ruined ring plain inside the Lunar crater Godin was discovered with the Meudon 83 cm refractor visually.

[20] It is noted as a difficult visual observation target from Earth, and it lies west of the crater peak.