46 THEORY OF LIGHT. 



HEAT. 



THE theories advanced with respect to the nature of caloric 

 aim at the conclusion, that it is a specific matter or body, 

 which by insinuating itself into the interstices between the par- 

 ticles or atoms of solid bodies, is supposed to impart to them 

 an expansive power, by which they appear to be placed at 

 greater relative distances, which if continued with increased 

 temperature, reduces the solid to a liquid, and by a further 

 continuance of action on fluids, converts them into the aeriform 

 or gaseous state. 



This contemplates the admission that there exists a matter 

 of heat, independently of a matter of light, and of that matter 

 which appears in the solid, fluid, and aeriform states ; and that 

 the transition of bodies from and to the three last described 

 alternations, is solely imputable to the matter of heat as a 

 direct cause. 



Now if heat was a distinct matter, we must suppose it to be 

 of a defined quantity, occupying space in all bodies, whether 

 solid, fluid, or gaseous ; and should naturally conclude that 

 if it were specific, to be accumulated in one position it must 

 be abstracted from another, which does not appear to be 

 established. 



Instead of,, being a cause, I would rather conclude it to be 

 an effect, arising from the energies of action exerted by the 

 constituents of light, to reunite in the form of radiant matter 

 by galvanic or electrical excitement. 



Thus, for example, when you take two pieces of dried wood 

 at a low temperature with smooth surfaces, by rubbing them 

 together for some little time, their surfaces become influenced 

 by opposite states of electricity ; they inflame, and the com- 

 bustion is continued until they are in part, or wholly, con- 

 sumed ; during this combustion a portion of light is evolved, 

 a portion of the solid matter is converted into the gaseous 



