from Terrestrial Sources, dT 



ficiently established that a portion of the heat of the radiating 

 body actually disappears, (at least in the form of radiant heat,) 

 or is in some way totally changed in its properties : yet it may be 

 worth while to observe, that the experiments now recorded, or 

 quoted, afford a more palpable confirmation of this conclusion. 



16. When we consider that in every part of a flame an intense 

 chemical action is going on, and a high temperature in consequence 

 generated, it will follow that if by any external means the inten- 

 sity of that action is increased, a proportional quantity of heat 

 must be generated, and the intensity of such action is increased in 

 the instance of a more complete combustion being produced by 

 external means. That the quantity of light evolved, and perhaps 

 also its intrinsic heating power, undergo an increase, whilst the 

 simple heat does not increase so fast, shews that of the increased 

 degree of heat generated by the more complete combustion, an in- 

 creasing portion is occupied in the production of light. 



17. The same truth is exemplified with additional force in the in- 

 stance of a flame whose light is increased by the greater evolution 

 of solid ignited particles, whilst its radiant heat does not sustain a 

 proportional increase. If a particle of solid matter be volatilized 

 into a flame of gas, the temperature of the gas is communicated to 

 it ; and the same temperature makes the solid particle give out 

 much more light (estimated by its heating effect) than the gas, 

 but not as much more heat. Therefore a portion of the heat 

 communicated to the solid particle disappears as radiant heat, and 

 is occupied in the evolution of light. 



1 8. In the experiments on uniting different flames, the same thing 

 is exhibited in a still more palpable manner. We there perceive 

 that the simple heat radiated from two flames united, is much less 

 than double that radiated from one. But yet, since by the junc- 

 tion of two equal masses of luminous matter at equal temperatures 

 the heat must be doubled, it is evident that a portion of it is ab- 

 stracted, and that at the expense of this portion the heating power 

 of the light is increased. 



We might argue in the same way from the experiments on in- 

 candescent metal. Since the total effect, or the values of Q + h) 



