284 POPULAR LECTURES AND ADDRESSES. 



seems to have been first called scientifically by 

 Robert Boyle about two hundred years ago. 



There are other rays which we do not perceive 

 in any of these ways, but which we do perceive by 

 our sense of heat : heat rays as they are commonly 

 called. But in truth all rays that we call light 

 have heating effect. Radiant heat and light are one 

 and indivisible. There are not two things, radiant 

 heat and light : radiant heat is identical with light. 

 Take a black hot kettle into a dark room, and 

 look at it. You do not see it. Hold your face 

 or your hand near it, and you perceive it by what 

 Bunyan would have called Feel Gate ; only now 

 we apply the word feeling to other senses as 

 well as Touch. You perceive it before you touch 

 it. You perceive it with the back of your hand, 

 or the front of your hand ; you perceive it with 

 your face, yes, and with your eye, but you do 

 not see it. You perceive it, even by your eye, 

 and still you do not see it. Well, now, must 

 I justify the assertion that it is not light ? You 

 say it is not light, and it is not so to you, if you 

 do not see it. There has been a good deal of 



