What does "as nearly as" means?

Question

Could you please explain the phrase "as nearly as could be discerned" in the following passage?

Suddenly Hewitt touched his companion's arm and pointed toward the window. A faint rustling sound was perceptible, and, as nearly as could be discerned in the darkness, some white blind or covering was placed over the glass from the inside. Arthur Morrison, Martin Hewitt, Investigator

Does this mean "as far as they could discern"?

Answer 1

Your interpretation is correct. The following do mean essentially the same thing:

as nearly as could be discerned
as far as they could discern

You'll note that the novel was published in 1894. Most experienced readers will agree that the style of this phrase is quite old-fashioned in fiction. Contemporary writers seldom use it unless they are going for a historical atmosphere.