I suppose your love will effervesce in six months, or less. I have observed in books written by men, that period assigned as the farthest to which a husband's ardour extends.
Chapter 24 · Jane Eyre
Context
Jane predicts that Rochester's passionate love will fade quickly after marriage, citing what she has read in books written by men about the typical duration of husbands' ardor.
Analysis
The scientific metaphor 'effervesce'—suggesting love as a chemical reaction that bubbles up and dissipates—deflates romantic passion into a predictable physical process. Jane's citation of 'books written by men' is pointed: she is using male authors' own cynicism about marriage against Rochester, turning patriarchal literature into evidence that his promises cannot be trusted, while the phrase 'husband's ardour' wryly notes that it is always the husband's feelings these books track.
Essay Tip
Support a thesis that Jane uses her reading as a form of power—by citing male-authored books about male inconstancy, she claims knowledge of how men like Rochester operate, countering his individual promises with generalized evidence and protecting herself through literary precedent.