I- 1 4 Inquiry concerning the Nature of Heat, 



than they are found to be, is not because they are mixed 

 with other reflected rays, but because they are few, the 

 greater part of the rays which the hot body actually 

 emits being reflected and turned back upon itself by the 

 reflecting surface by which it is immediately surrounded. 



The reflecting surface at which the rays of light which 

 impinge against the polished surface of any solid or 

 fluid body are turned back and reflected is actually situ- 

 ated without the body, and even at some distance from 

 it ; this has been proved by the most decisive experi- 

 ments ; and there are so many striking analogies be- 

 tween the rays of light and those invisible rays which 

 all bodies at all temperatures appear to emit, that we 

 can hardly doubt of their motions being regulated by 

 the same laws. 



Perhaps there may be no other difference between 

 them than exists between those vibrations in the air 

 which are audible and those which make no sensible im- 

 pression on our organs of hearing. 



If the ear were so constructed that we could hear all 

 the motions which take place in the air, we should, no 

 doubt, be stunned by the noise; and if our eyes were 

 so constructed as to see all the rays which are emitted 

 continually, by day and by night, by the bodies which 

 surround us, we should be dazzled and confounded by 

 that insupportable flood of light poured in upon us on 

 every side. 



Taking it for granted that these invisible radiations 

 exist, we will endeavour to trace the effects which must 

 necessarily be produced by them, and see if these in- 

 vestigations will not lead us to a discovery of the causes 

 of some appearances which have hitherto been envel- 

 oped in much obscurity. 



