I think the reason Darcy attends the assembly is boredom—a strange house with a desperately small library, no letter to write and no friends in the neighborhood but those attending the assembly. I think Darcy’s trying not to look at Lizzy in Ch. 15 is a perfect example of the war between his attraction to Lizzy and his need to avoid “the danger of paying Elizabeth too much attention” (11). The first makes him want to look at her and the second to look anywhere else.

I think Darcy’s courtesy is so much awakened that he probably did not consider going to bed as Bingley suggested in Ch. 11 and reconciled himself to attending his friend’s ball which bid fairer having the advantage of being private. Did Darcy go with an idea of avoiding Lizzy or just that he could see her without danger? At the ball Darcy first goes to Lizzy to make “polite inquiries” but is received with only tolerable civility—maybe as Adrian suggests he noticed her ill-humor and retreated. Perhaps he watched her dancing with Mr. Collins and then an officer and felt he must satisfy a desire to do the same. It could be he walks away after her acceptance because she was speaking with Charlotte and he did not wish to join them or went away to steel himself to withstand being in close proximity to Lizzy for a half hour!

I think Darcy’s initial silence during their dance may be because he usually does not talk much while dancing for he asks Lizzy “Do you talk by rule, then, while you are dancing?” and his mind might also have been engaged with his conflicting feelings about Lizzy. Although distracted he also seems obliging. When Lizzy admonished him for silence he “smiled, and assured her that whatever she wished him to say should be said” but it is a bit difficult for Darcy because Lizzy is decidedly contrary due to her anger over Wickham’s absence. She continues to verbally poke him by referring to his behavior at the assembly in comparing private and public balls, about his failures as a conversationalist and when he does try again by asking “if she and her sisters did not very often walk to Meryton” Lizzy prods him further by alluding to their meeting Wickham.

I think Darcy is surprised at Lizzy’s sympathy for Wickham and the assertion that he has done wrong to him. He wishes to change the subject but then Sir William comes along and his allusions to a marriage between Jane & Bingley “strike him [Darcy] forcibly” and so much so Darcy looks seriously at them dancing and has to recover himself to turn his attention back to Lizzy. Asking her what they were talking of Lizzy disavowals that they were speaking at all, they have nothing to say having tried “two or three subjects already without success”. Darcy brings up the subject of books which Lizzy shoots down and asks about his “Implacable resentment” (11) and if he is “very cautious, I suppose, as to its being created” to which his replies in the affirmative do nothing to persuade Lizzy.

Darcy asks Lizzy’s purpose in these questions about him and she says, trying to be less grave, that it is to discover his character and again at his question that she is puzzled by differing accounts of him so as to “not get on at all”. Darcy readily believes “report may vary greatly with respect to me” and wishes she would not sketch his character at present gravely fearing “the performance would reflect no credit on either” which I think means she could only judge him poorly being influenced (misled) by Wickham? Lizzy persists suggesting she may have no other opportunity. Darcy, offended I think because she persists, coldly responds “I would by no means suspend any pleasure of yours” and they speak no more and part dissatisfied. He less dissatisfied than she because he has a “tolerable powerful feeling towards her, which soon procured her pardon, and directed all his anger against” Wickham.

She was at least free from the offence of Mr. Darcy's farther notice; though often standing within a very short distance of her, quite disengaged, he never came near enough to speak. She felt it to be the probable consequence of her allusions to Mr. Wickham, and rejoiced in it.