Jane Eyre, writing homework help: Jane Eyre is divided into three volumes

Jane Eyre is divided into three volumes and also takes place in three (okay, maybe four) main settings: Gateshead and Lowood (childhood), Thornfield (young love), Moor House/Morton (temporary banishment). But the volumes don’t match up exactly with the three main sections of the plot. Why does the novel break after Volume 1, Chapter 15 (Jane saves Rochester from burning to death in his bed) and again after Volume 2, Chapter 11 (Jane discovers Rochester’s attempt at bigamy)? What might the events of these two chapters have in common?