and the Economy of Fuel. 31 



short, without bewildering myself and my reader in 

 this endless labyrinth of darkness and uncertainty, I 

 shall confine my inquiries to objects more useful, and 

 which are clearly within the reach of human investiga- 

 tion ; namely, the discovery of the sensible properties 

 of heat, and of the most advantageous methods of gen- 

 erating it, and of directing it with certainty and effect 

 in those various processes in which it is employed in 

 the economy of human life. 



Though I do not undertake to determine what heat 

 really is. nor even to offer any opinions or conjectures 

 relative to that subject ; yet as heat is evidently some- 

 thing capable of being excited or generated, increased 

 or accumulated, measured and transferred from one 

 body to another, in treating the subject I shall speak 

 of it as being generated, confined, directed, dispersed, 

 etc., it being necessary to use these terms in order to 

 make myself understood. 



Though it is not known exactly how much heat it is 

 possible to produce in the combustion of any given 

 quantity of any given kind of fuel, yet it is more than 

 probable that the quantity depends in a great measure 

 on the management of the fire. It is likewise probable 

 I might say certain that the heat produced is fur- 

 nished not merely by the fuel, but in a great measure, 

 if not entirely, by the air by which the fire is fed and 

 supported. It is well known that air is necessary to 

 combustion ; it is likewise known that the pure part of 

 common atmospheric air, or that part of it (amounting 

 to about -5- of its whole volume) which alone is capable 

 of supporting the combustion of inflammable bodies, 

 undergoes a remarkable change, or is actually decom- 

 posed in that process ; and as in this decomposition of 



