Adrian> At the same time, I think that Henry, unlike Catherine, does not believe Isabella loves James.

I agree, and I like the way Catherine takes a little time to absorb the idea:

“It is probable that she will neither love so well, nor flirt so well, as she might do either singly. The gentlemen must each give up a little.”

After a short pause, Catherine resumed with, “Then you do not believe Isabella so very much attached to my brother?”

One of the great things about chapter 19 is how Henry puts most of his effort into cool-headed reasoning, but avoids giving a flat contradiction to Catherine's faith in Isabella's good-will. Only when that fails to comfort Catherine does he change tack, and offer the information that Frederick will be leaving soon. The really cute thing about the change of tack is that it comes immediately after "... one will never tease the other beyond what is known to be pleasant." He's taking his own advice, and not teasing/tormenting/instructing Catherine with too much cool-headed reasoning when it really doesn't seem to be helping.

The not-so-great things in ch19, IMO, are...

• Henry's last two approaches contradict each other. If James cannot think that he's safe (from Isabella straying) only in solitude, what good is the solitude of Frederick leaving Bath? It's a bit unfortunate that Henry backs himself into that corner, and that Catherine seems to draw part of her comfort from one point and part from the other.

• "To be guided by second–hand conjecture is pitiful" is overly harsh. It implies "What you're trying to do is pitiful." Henry could have made his point equally well by just leaving out that sentence.