The most noteworthy development of the open fireplace took place in 1796, when Englishman Count Rumford published his comprehensive essay, "Chimney Fireplaces."... the inclined fireback... increased fireplace efficiency by providing an area of greater radiation. For the purpose of breaking up the current of smoke in the event of chimney down draft, the back smoke shelf of Rumford's improved fireplace ended abruptly—a practice strictly adhered to by fireplace masons to this day.

The Owner Built Home: A How-to-do-it Book (1972)