"Another very common fault... in chimney fire-places, that have been altered on what have been called my principles, and which has a direct tendency to bring dust, and even smoke, into the room, is the sloping of the covings too much, and leaving the opening of the fire-place in front too wide. I have said, in my Essay on Chimney Fire-places, that where chimnies are well constructed, and well situated, and have never been apt to smoke, in altering them the covings may be placed at an angle of 135 degrees with the back; but... that they should never exceed that angle, and... bad consequences... must follow from making the opening of a fire-place very wide, when its depth is very shallow..."