William and John Herschel used an 18.5” aperture, 20’ long speculum reflector to find DSO. (Speculum metal is a mixture of around two-thirds copper and one-third tin)
Was their telescope better than an 11” refractor? Was it better than a 16” refractor?
One way to find out is to look at the magnitudes of the galaxies they found.
The number of galaxies seen should increase as the magnitude increases.
If it does not increase we have reached a working magnitude limit.
For William Herschel the working magnitude limit was about 13.
For John Herschel the working magnitude limit was about 12.8 or 12.9.
For Heinrich D’Arrest’s 11” refractor it was about magnitude 13.5 or 13.7.
For Lewis Swift’s 16” refractor it was about magnitude 13.7 or 13.9.
They all saw galaxies much fainter than that, but they also missed many that were fainter than their working magnitude limit.
So an 11" refractor was probably better than the Herschel’s 18.5” reflector.
(Or maybe d’Arrest had better eyesight)
There are 402 galaxies brighter than magnitude 11.1.
The Milky Way, the two Magellan Clouds and M31 in Andromeda were seen before the invention of the telescope in 1608. After that M33 was found by Giovanni Hodierna in 1654, M32 by Guillaume Legentil in 1749 and M83 by Nicolas-Louis Lacaille in 1752.
Most (93%) of the 402 bright galaxies were found by 8 men
244 galaxies were found by William Herschel with an 18.7” aperture speculum reflector *
51 by his son John Herschel with the same telescope
37 by James Dunlop with a 9” aperture speculum reflector
* Speculum metal is a mixture of around two-thirds copper and one-third tin.
18 by Pierre Mechain with a 3” refractor
10 by Charles Messier with a 3.5” refractor
6 by Edward Emerson Barnard with 5”, 6” and 12” telescopes
6 by Lewis Swift with a 16” refractor and
5 by Johann Koehler, his telescope’s aperture is not known.
William Herschel found most of the 244 bright galaxies from Slough near Windsor Castle in England between 1783 and 1802. John Herschel found one bright galaxy from Slough in 1829, the remaining 50 were discovered from Cape Town between 1834 and 1837.
Dunlop found 37 bright southern galaxies from Parramatta, NSW in 1826.
Mechain and Messier found their 28 galaxies from Paris in 1779 to 1781 (Mechain) and 1771 to 1781 (Messier).
Barnard discovered 6 bright galaxies between 1883 and 1890 from Vanderbilt and Lick, USA.
Swift found 6 bright galaxies between 1885 and 1898 from New York state and California.
Koehler found 5 Virgo galaxies in 1779 from Dresden, Germany - M59, 60, 84, 86 and 87.
