is there any speical meaning in this usage?
this paragraph is from Austin's "Pride and Prejudice", i don't understand why "an union" ,not "a union?"
It was an union that must have been to the advantage of both; by her ease and liveliness, his mind might have been softened, his manners improved, and from his judgment, information, and knowledge of the world, she must have received benefit of greater importance. But no such happy marriage could now teach the admiring multitude what connubial felicity really was. An union of a different tendency, and precluding the possibility of the other, was soon to be formed in their family.