"In the course of my numerous experiments upon Chimnies I have taken much pains to determine the width proper to be given to this passage, and I have found that, when the back of the Fire-place is of the proper width, the best width for the throat of the Chimney, when the Chimney and the Fire-place are of the usual form and size, is four inches. Three inches might sometime answer, especially where the Fire-place is very small, and the Chimney good, and well situated; but as it is... of much importance to prevent those accidents... putting too many coals at once upon the fire... when the throats of Chimnies were... very narrow..."