Here follows a list of telescopes Messier listed and stated he used in 1765-69, published in the Connaissance des Temps for 1807 (here taken from Kenneth Glyn Jones' book; FL means "Focal Length", "Mag." Magnification, unfortunately he normally doesn't give the aperture):
Although some of Messier's reflecting telescopes had 7.5 to 8 inch aperture, they had little light gathering power as their mirrors were made of speculum metal (glass mirrors came in use only in the 1850s).
In his contribution to Sky & Telescope which is reprinted in Mallas' and Kreimer's Messier Album, Owen Gingerich points out that Messier's favorite instrument was a 32-feet FL, 7.5-inch aperture Gregorian reflector with mag. 104x, not listed above. Bailly has computed that the effective aperture of this instrument was equivalent to a 3.5-inch refractor. Even worse was the situation for the old Newtonian reflector he came over from Delisle, which was an 8-inch but as effective as a 2.5-inch refractor only, so it was little used, although it seems this was the "original" instrument at Hotel de Cluny, Messier's observatory. Later he preferred to use several 3.5-inch (90 mm) achromatic refractors, which were usually about 3.5 feet long and magnifying 120 times. He selected to use these scopes because they were the best accessible instruments for him.
It remains to state that all of Messier's instruments could probably not compete with a modern 4-inch refractor (or unobstructed reflector, e.g., a Schiefspiegler) or 6-inch Newton reflector. Therefore, even moderately equipped amateurs of current days can easily hunt down all the objects he observed and cataloged.
Last Modification: 7 Feb 1998, 18:10 MET