498 Of Chimney Fireplaces. 



probable that the combined heat can only be communi- 

 cated to other bodies by actual contact with the body with 

 which it is combined ; and with regard to the rays which 

 are sent off by burning fuel, it is certain that they com- 

 municate or generate heat only when and where they are 

 stopped or absorbed. In passing through air, which is 

 transparent, they certainly do not communicate any heat 

 to it; and it seems highly probable that they do not 

 communicate heat to solid bodies by which they are 

 reflected. 



In these respects they seem to bear a great resem- 

 blance to the solar rays. But n order not to distract 

 the attention of my reader or carry him too far away 

 from the subject more immediately under consideration, 

 I must not enter too deeply into these inquiries respect- 

 ing the nature and properties of what has been called radi- 

 ant heat. It is certainly a most curious subject of philo- 

 sophical investigation, but more time would be required 

 to do it justice than we now have to spare. We must, 

 therefore, content ourselves with such a partial examina- 

 tion of it as will be sufficient for our present purpose. 



A question which naturally presents itself here is, 

 What proportion does the radiant heat bear to the com- 

 bined heat ? Though that point has not yet been de- 

 termined with any considerable degree of precision, it 

 is, however, quite certain, that the quantity of heat 

 which goes off combined with the smoke, vapour, and 

 heated air, is much more considerable, perhaps three or 

 four times greater, at least, than that which is sent off 

 from the fire in rays. And yet, small as the quantity is 

 of this radiant heat, it is the only part of the heat gene- 

 rated in the combustion of fuel burned in an open fire- 

 place, which is ever employed, or which can ever be em- 

 ployed, in heating a room. 



