Of Chimney Fireplaces. 509 



The answer is short, and easy to be understood, bring 

 it forward as far as possible, without diminishing too 

 much the passage which must be left for the smoke. 

 Now as this passage, which, in its narrowest part, I 

 have called the throat of the chimney^ ought, for reasons 

 which are fully explained in the foregoing chapter, to be 

 immediately, or perpendicularly, over the fire, it is evi- 

 dent that the back of the chimney must always be built 

 perfectly upright. To determine therefore the place for 

 the new back, or how far precisely it ought to be 

 brought forward, nothing more is necessary than to as- 

 certain how wide the throat of the chimney ought to be 

 left, or what space must be left between the top of the 

 breast of the chimney, where the upright canal of the 

 chimney begins, and the new back of the fireplace carried 

 up perpendicularly to that height. 



In the course of my numerous experiments upon 

 chimneys, 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 fireplace is of a 

 proper width, the best width for the throat of a 

 chimney, when the chimney and the fireplace are at the 

 usual form and size, is four inches. Three inches might 

 sometimes answer, especially where the fireplace is very 

 small, and the chimney good, and well situated; but as 

 it is always of much importance to prevent those acci- 

 dental puffs of smoke which are sometimes thrown into 

 rooms by the carelessness of servants in putting on sud- 

 denly too many coals at once upon the fire, and as I 

 found these accidents sometimes happened when the 

 throats of chimneys were made very narrow, I found 

 that, upon the whole, all circumstances being well con- 

 sidered, and advantages and disadvantages compared 



