HEAT, COLD, AND LIGHT. 317 



white bodies are, or the more highly they are 

 polished, the less they are heated, because they 

 reflect more of the rays : and when a body is per- 

 fectly white it reflects all the light, and is not 

 heated at all. 



Bodies, in proportion as they deviate from white a 

 destroy the more solar rays, and a perfectly black 

 ?Jody would destroy them all : hence bodies are 

 more heated, ccet. par. as they are darker coloured, 

 by this cause of Heat. 



When a body is rough, asi f we make a piece of 

 glass so (which may have no colour) it destroys 

 part of the rays, or, at least, suffers them to ap- 

 proach' so near its surface before it reflects thein 

 that they cause it to be heated. 



Thus far our reasonings induce us to suppose 

 that Heat i8 a quality: but Heat, as a quality, 

 cannot exist without a substance to exist in. So 

 that, if it were possible to produce a perfect va- 

 cuum, there could be no Heat therein. This also 

 leads us to conclude, that tiie denser a body is, 

 the more Heat may be therein produced ; other 

 circumstances being: the same. 



Heai, it is affirmed, can only be produced by 

 the solar rays at the surfaces of bodies : conse- 

 quently the interior parts can only be heated by 

 communication. And if we ketp in mind that 

 Heat is more rtadily transmitted, communicated, 

 and received, by some bodies than others ; it will 

 then appear that, as a' body receives Heat with. 

 more facility, it will be the mere heated by the 



sun's 



