* 



and the Economy of Fuel. 39 



But in order to be able to form a clear and distinct 

 idea upon this subject, it is necessary to examine with 

 care all the circumstances attending the generation of 

 heat in the combustion of inflammable bodies, and to 

 see in what manner or under what form the heat gen- 

 erated manifests itself and how it may. be collected, 

 accumulated, confined, and directed. 



This opens a wide field for philosophical inquiry ; but 

 as these investigations are not only curious and enter- 

 taining, but also useful and important in a high degree, 

 I trust my reader will pardon me for requesting his par- 

 ticular attention while I endeavour to do justice to this 

 most interesting, but, at the same time, most abstruse 

 and most difficult part of the subject I have undertaken 

 to treat. 



The heat generated in the combustion of fuel mani- 

 fests itself in two ways; namely, in the hot vapour 

 which rises from the fire, with which it may be said to 

 be combined, and in the calorific rays which are thrown 

 off from the fire in all directions. These rays may, 

 with greater propriety, be said to be calorific, or capable 

 of generating heat, in any body by which they are 

 stopped, than to be called hot; for when they pass 

 freely through any medium (as through a mass of air, 

 for instance), they are not found to communicate any 

 heat whatever to such medium; neither do they appear 

 to excite any considerable degree of heat in bodies 

 from whose surfaces they are reflected ; and in these 

 respects they bear a manifest resemblance to the rays 

 emitted by the sun. 



What proportion this radiant heat (if I may be 

 allowed to use so inaccurate an expression) bears to 

 that which goes off from burning bodies in the smoke 



