I have a basic understanding of the impact of phrenology, but a knowledge that "it was popular" is pretty surface when it comes to understanding passages like

“Just so; I think so; and you shall be answerable for it.  Criticise me: does my forehead not please you?”

He lifted up the sable waves of hair which lay horizontally over his brow, and showed a solid enough mass of intellectual organs, but an abrupt deficiency where the suave sign of benevolence should have risen.

“Now, ma’am, am I a fool?”

“Far from it, sir.  You would, perhaps, think me rude if I inquired in return whether you are a philanthropist?”

“There again!  Another stick of the penknife, when she pretended to pat my head: and that is because I said I did not like the society of children and old women (low be it spoken!).  No, young lady, I am not a general philanthropist; but I bear a conscience;” and he pointed to the prominences which are said to indicate that faculty, and which, fortunately for him, were sufficiently conspicuous; giving, indeed, a marked breadth to the upper part of his head: “and, besides, I once had a kind of rude tenderness of heart..."

As characters within their own story, they seem to share a visual knowledge of phrenology with which to interpret their own foreheads as well as to consider evaluating each other by such a method as being a matter of course; on a meta level, Charlotte Bronte included this kind of thing in a book that ended up being very popular with apparently no compunctions and every expectation that people would know exactly what she was talking about.

Was phrenology (or whatever the specific analysis of foreheads may have been called) really that common?