Of Chimney Fireplaces. 493 



has hitherto been left larger than otherwise it probably 

 would have been made, in order to give a passage to the 

 chimney-sweeper; but I shall show hereafter how a 

 passage for the chimney-sweeper may be contrived with- 

 out leaving the throat of the chimney of such enor- 

 mous dimensions as to swallow up and devour all the 

 warm air of the room, instead of merely giving a pas- 

 sage to the smoke and heated vapour which rise from 

 the fire, for which last purpose alone it ought to be 

 destined. 



Were it my intention to treat my subject in a formal 

 scientific manner, it would doubtless be proper, and 

 even necessary, to begin by explaining in the fullest 

 manner, and upon the principles founded on the laws 

 of nature, relative to the motions of elastic fluids, as 

 far as they have been discovered and demonstrated, the 

 causes of the ascent of smoke; and also to explain and 

 illustrate upon the same principles, and even to measure 

 or estimate by calculations, the precise effects of all 

 those mechanical aids which may be proposed for assist- 

 ing it in its ascent, or rather for removing those ob- 

 stacles which hinder its motion upwards ; but as it is 

 my wish rather to write a useful practical treatise than a 

 learned dissertation, being more desirous to contribute 

 in diffusing useful knowledge by which the comforts 

 and enjoyments of mankind may be increased, than to 

 acquire the reputation of a philosopher among learned 

 men, I shall endeavour to write in such a manner as to 

 be easily understood by those who are most likely to profit 

 by the information I have to communicate^ and consequently 

 most likely to assist in bringing into general use the 

 improvements I recommend. This being premised, I 

 shall proceed, without any further preface or introduc- 



