Re: NA, Chapter 23: Time slows down; Light and Dark
Another aspect of these two chapters is the slowing down of time so that much verbal space is taken up with one morning. But what fills Catherine's mind excites her so that she lives vividly and intently. This slowing down of time is important in the feel we have of a shift from the Bath to these Northanger Chapters. If the romance of the second of this week's chapters is counterpointed or undercut by Catherine's mad (but not wholly inexplicable) delusoin, this second part is as strong in effective use of light and dark. Through these chapters Austen uses real time to cast shadows, throw cheerful light, and then leave Catherine in some pale space so as to reinforce a highly varied and rather subtle group of moods.
Consider the slowness and picture given us at the close of Chapter 23:
" The side of the quadrangle, in which she supposed the guilty scene to be acting, being, according to her belief, just opposite her own, it struck her that, if judiciously watched, some rays of light from the general's lamp might glimmer through the lower windows, as he passed to the prison of his wife; and, twice before she stepped into bed, she stole gently from her room to the corresponding window in the gallery, to see if it appeared; but all abroad was dark, and it must yet be too early. The various ascending noises convinced her that the servants must still be up. Till midnight, she supposed it would be in vain to watch; but then, when the clock had struck twelve, and all was quiet, she would, if not quite appalled by darkness, steal out and look once more. The clock struck twelve--and Catherine had been half an hour asleep" (1995 Penguin, Butler ed, pp 164-5).
Re: NA, Chapter 23: Henry's Absence
Then there's Henry's absence -- another "device" which creates the peculiar atmosphere of these chapter is the removal of Henry Tilney. The atmosphere would not last an instant were his wit there to undercut the dreams, his sanity and strong presence (as a male) to keep his father under control. Catherine says Henry is much missed, but with him there these chapters would not have the same effect. It is when Henry is not around that Catherine's imagination gets full play.