LIGHT, COLOR, AND SOUND 221 



example, leaves look green to us not exactly because they 

 are green (though it is quite right to say they are), but 

 because the light which they fail to absorb and which 

 they reflect back to our eyes produces an effect of green. 



Surely you have noticed that the color of objects is not 

 quite the same when viewed by artificial light as when 

 viewed by daylight; thus, by artificial light it is hard to 

 tell blue from green. Evidently, then, the color of an 

 object depends to some extent upon the nature of the light 

 that is shining upon it. 



This suggests an interesting and significant fact. If 

 gaslight, for example, produces light effects that are differ- 

 ent from those produced by sunlight, does it not follow 

 that the spectrum of gaslight will be different from the 

 spectrum of sunlight? If an object which is blue in sun- 

 light is not blue in another kind of light, does it not follow 

 that the other kind of light lacks blue rays? For surely 

 the object does not change its nature whenever it is changed 

 from one kind of light into another; the change of color 

 must be due to differences in the kinds of light. 



Such thoughts as these led scientists to examine care- 

 fully the spectra produced by various kinds of light, and 

 it was found to be a fact that every kind of substance capa- 

 ble of releasing light releases a kind which is di/erent from 

 all other kinds. Thus certain substances when they burn 

 release light which contains no blue rays. Thus we see 

 why an object blue by daylight may fail to be blue by 

 artificial light. 



Now since it has been found that every kind of substance 

 when it burns releases its own kind of light, it follows that 

 if the spectrum characteristic of a certain substance be 

 known, then it may be possible to tell what a substance 



