I wonder why the author(Dickens) says; "In his own meditations" and not "their own mediatations" in this sentence? Is possible to say 'their' too?
I wish I spoke English like him .
"Each immersed in his own meditations."
The subject of this sentence is the pronoun each, which is a singular pronoun. The possessive pronoun his has to agree in number with that subject.
Since English does not have a gender-neutral third person singular possessive pronoun, many modern writers and grammarians have begun to use the third person plural possessive their to avoid the risk of offending women who do not wish to be addressed by a masculine pronoun.
In Dickens's time this was not the case.