Of Chimney Fireplaces. 497 



warm a room, it is necessary, first of all, to contrive 

 matters so that the room shall be actually warmed ; 

 secondly, that it be warmed with the smallest expense 

 of fuel possible ; and, thirdly, that, in warming it, the 

 air of the room be preserved perfectly pure and fit for 

 respiration, and free from smoke and all disagreeable 

 smells. 



In order to take measures with certainty for warming 

 a room by means of an open chimney fire, it will be 

 necessary to consider how, or in what manner, such a fire 

 communicates heat to a room. This question may per- 

 haps, at the first view of it, appear to be superfluous 

 and trifling, but a more careful examination of the 

 matter will show it to be highly deserving of the most 

 attentive investigation. 



To determine in what manner a room is heated by an 

 open chimney fire, it will be necessary, first of all, to 

 find out under what form the heat generated in the com- 

 bustion of the fuel exists, and then to see how it is 

 communicated to those bodies which are heated by it. 



In regard to the first of these subjects of inquiry, it 

 is quite certain that the heat which is generated in the 

 combustion of the fuel exists under two perfectly dis- 

 tinct and very different forms. One part of it is com- 

 bined with the smoke, vapour, and heated air, which rise 

 from the burning fuel, and goes off with them into the 

 upper regions of the atmosphere ; while the other part, 

 which appears to be uncombined, or, as some ingenious 

 philosophers have supposed, combined only with light, 

 is sent off from the fire in rays in all possible directions. 



With respect to the second subject of inquiry, 

 namely, how this heat, existing under these two differ- 

 ent forms, is communicated toother bodies ; it is highly 



VOL. n. 32 



