and the Mode of its Communication. 113 



they are neither heated nor cooled by the rays so re- 

 flected, their temperatures are slowly changed by the 

 actions of the surrounding bodies at a different tem- 

 perature. 



When a hot polished metallic body is exposed in the 

 air to cool, surrounded by other bodies at the same 

 temperature as that of the cold air, most of the rays 

 from the surrounding bodies are reflected at the pol- 

 ished surface of the hot body ; it is evident, then, that 

 two sorts of rays must proceed from the surface of that 

 body, namely, those calorific rays which it emits, and 

 those other rays (which with regard to the surround- 

 ing bodies are neither calorific nor frigorific) which it 

 reflects. 



On a cursory view of the subject, one might be led 

 to imagine that, as the rays which proceed from the hot 

 metallic body are of two kinds, the energy of the calo- 

 rific rays, which properly belong to the hot body, might 

 be diminished by those other reflected rays by which 

 they are accompanied, and with which they may be said 

 to be mixed ; but a more careful examination of the 

 matter will show that this cannot be the case, that is 

 to say, as long as all the surrounding bodies continue 

 to be at the same temperature. If the temperature of 

 the surrounding bodies be different, such of them will 4 

 be affected by the reflected rays as happen to be of a 

 temperature different from that from which the ray 

 originated ; but still the effects produced by the rays 

 emitted by the hot body will be the same, or their 

 power of effecting changes in the temperatures of other 

 (hotter or colder) bodies will remain undiminished and 

 unchanged. 



The reason why their effects are not more powerful 

 VOL. n. 8 



