I detest the "an histor*" construction. It makes no sense logically and I've never really seen a truly cogent argument in its favour. As a matter of plain English, I change it to "a histor*" in texts I'm editing.

(Before any readers get too outraged, I generally edit newspaper articles. Were I going through someone's book, I'd leave it as-is because it's part of their authorial voice -- much as I'd hate doing so.)