LIGHT 233 



Absorption of Light and Color Phenomena. Color 

 depends upon the wave length of light. Only wave lengths 

 within a certain limit affect the nerves of sight, namely 

 those between .0000689 cm. and .0000397 cm. in length. 

 There are many ether waves both longer and shorter than 

 these, but they are not visible. White light contains 

 all the colors of the spectrum from red to violet inclusive. 

 Most artificial light is deficient in some of the colors of 

 the spectrum and is therefore not white light. For ex- 

 ample, the mercury vapor electric lamp gives a light 

 which is deficient in red waves. When objects are 

 viewed in such a light, they have a ghostly appearance. 

 Why? 



If a piece of red glass is held in the path of the spec- 

 trum, all the colors except the red will disappear, showing 

 that all the wave lengths, except the wave length which 

 produced red, have been absorbed by the glass. Try 

 glass of other colors in the same way. It will be found 

 that glass of certain colors has greater power of absorbing 

 light than glass of other colors. Red is one of the best 

 absorbers of other colors. 



Most substances absorb light to some degree. The 

 absorbed light reappears as heat energy or chemical 

 energy. The light that falls on an object and is not ab- 

 sorbed is reflected. The color which a body has in or- 

 dinary daylight is determined by wave lengths which are 

 not absorbed by the body. If a body appears white in 

 daylight, it is because it reflects or disperses all wave 

 lengths and does not absorb one kind of wave length more 

 than the other. If a body appears red in daylight, it is 

 because it absorbs other rays more readily than it does 

 red rays, so that the light which is reflected contains a 

 large proportion of red waves. A body appears blue or 



