and the Economy of Fuel. 57 



ing heat, and in no other way ; and if I succeed in this, 

 I fancy I may consider the proposition as sufficiently 

 proved. 



The effect of a blast of cold air in cooling any hot 

 body exposed to it is well known, and the causes of this 

 effect may easily be traced to that property of air which 

 renders it a non-conductor of heat ; for if the particles 

 of cold air in contact with a hot body could, with per- 

 fect facility, give the heat they acquire from the hot 

 body to other particles of air by which they are imme- 

 diately surrounded, and these again to others, and so 

 on, the heat would be carried off as fast as the hot body 

 could part with it> and any motion of the particles of 

 the air, any wind or blast, would not sensibly facilitate 

 or hasten the cooling of the body ; and by a parity of 

 reasoning it may be show r n that, if flame were in fact a 

 perfect conductor of heat, any cold body plunged into 

 it would always be heated as fast as that body could 

 receive heat ; and neither any motion of the internal 

 parts of the flame, nor the velocity with which it im- 

 pinged against the cold body, could have any sensible 

 effect either to facilitate or accelerate the heating of 

 the body. But if flame be a non-conductor of heat, its 

 action will be exactly similar to that of a hot wind, and 

 consequently much will depend upon the manner in 

 which it is applied to any body intended to be heated 

 by it. Those particles of it only which are in actual 

 contact with the body will communicate heat to it ; and 

 the greater the number of different particles of the 

 flame which are brought into contact with it, the greater 

 will be the quantity of heat communicated. Hence the 

 importance of causing the flame to impinge with force 

 against the body to be heated, and to strike it in such 



