CHAPTER XXVIII 

 LIGHT, COLOR, AND SOUND 



We have noted that combustion' may result in light, 

 heat, or motion, or in combinations of these. To heat 

 and motion we have already given considerable attention. 

 It is time now to study light and to learn something of 

 its nature and behavior. 



Light and Heat Much Alike. The first thing for us to 

 appreciate is that light and heat are much alike. They 

 are both forms of radiant energy. Their apparent great 

 differences are due to the differences in the effects they 

 produce on us. 



This sameness-of-nature or kinship of light and heat is 

 indicated by many familiar phenomena. We know that 

 heat may be very readily transformed into light; similarly, 

 light may be transformed into heat. We know that 

 white clothes are cooler than dark clothes, even though 

 of the same weight; this is because white clothes reflect 

 the light, while dark clothes absorb it, and transform part of 

 it into heat. We know that sunlight striking through 

 glass, as in greenhouses, causes increase of temperature 

 even though the air outside may be cold; this is because 

 the light-rays are absorbed after they pass through the 

 glass, some of them are transformed into heat, and the 

 heat-rays cannot escape by passing through the glass as 

 the light-rays did. We know that in burning, both light 

 and heat usually appear, and it is hard to tell where one 

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