"[M]en... disccovered, that when the fire was surrounded with a wall to any considerable height, the motion of the wind was interrupted by it, and the smoke allowed to rise upwards till it reached the top of the building.—The free ascent of this disagreeble vapour... was promoted by the addition of a roof... Hence... in every part of the globe the first and most simple huts... are circular buildings, with a conical roof; in the middle of which, for the most part, is left a hole for the emission of the smoke; the fire having been placed in the centre of the building immediately below the opening, which served instead of a window, as well as a vent-hole for the smoke."