

THE WAVE THEORY OF LIGHT. 317 



near, but not over, a set of hot water pipes used 

 for heating a house ; the thing we perceive in 

 our faces and hands when we go near a boiling 

 pot and hold the hand on a level with it, is 

 radiant heat ; the heat of the hands and face caused 

 by a hot fire, or by a hot kettle when held under 

 the kettle, is also radiant heat. 



You might readily make the experiment with 

 an earthen teapot ; it radiates heat better than 

 polished silver. Hold your hands below the teapot 

 and you perceive a sense of heat ; above it you 

 get more heat ; either way you perceive heat. If 

 held over the teapot you readily understand that 

 there is a little current of hot air rising ; if you 

 put your hand under the teapot you find cold air 

 rising, and the upper side of your hand is heated 

 by radiation while the lower side is fanned and 

 is actually cooled by virtue of the heated kettle 

 above it. 



That perception by the sense of heat, is the 

 perception of something actually continuous with 

 light. We have knowledge of rays of radiant heat 

 perceptible down to (in round numbers) about 



