He arranges a selection from his observations on the nebulae in such a way as to give great plausibility to his view of the gradual transmutation of nebulae into stars Herschel begins by showing us that there are regions in the heavens where a faint diffused nebulosity is all that can be detected by the telescope.
It is thus possible to exhibit a series of objects beginning at one end with the most diffused nebulosity and ending at the other with an ordinary fixed star or group of stars.
This group is particularly rich in bright stars, and is full of nebulosity, but there are fewer faint stars than in equal areas of the surrounding sky; the central star is Alcyone (3rd magnitude); PleIone and Atlas are also of the 3rd magnitude.
Subsequent photographs showed that this nebula, which consisted mainly of two incomplete rings of nebulosity, was expanding outwards at the rate of from 2" to 3" per day.
This may explain the existence of gaseous nebulae, which are often found intimately associated with star-clusters, a good example being the nebulosity surrounding the Pleiades.