136 COLOR 



the red ray passes through the red glass, reaches the eye, 

 and produces a sensation of color. 



If a piece of blue glass is substituted for the red glass, the 

 blue band remains on the wall, while all the other colors dis- 

 appear. If both blue and red pieces of glass are held in the 

 path of the beam, so that the light must pass through first 

 one and then the other, the entire spectrum disappears and 

 no color remains. The blue glass absorbs all of the rays 

 except the blue ones, and the red glass will not allow these 

 blue rays to pass through it ; hence no light is allowed pas- 

 sage to the eye. 



An emerald looks green because it transmits green, and 

 absorbs all the other six colors of which ordinary daylight is 

 composed. A diamond appears white because it allows the 

 passage through it of all the various rays ; this is likewise 

 true of water and window panes. 



Stained-glass windows owe their charm and beauty to the 

 presence in the glass of various dyes and pigments which 

 absorb in different amounts some colors from white light and 

 transmit others. These pigments or dyes are added to the 

 glass while it is in the molten state, and the beauty of a 

 stained-glass window depends largely upon the richness and 

 the delicacy of the pigments used. 



130. Reflected Light. Opaque Objects. In Section 106 

 we learned that most objects are visible to us because of the 

 light diffusely reflected from them. A white object, such as 

 a sheet of paper, a whitewashed fence, or a table cloth, absorbs 

 little of the light which falls upon it, but reflects nearly all, 

 thus producing the sensation of white. A red carpet absorbs 

 all the light rays incident upon it except the red rays, and 

 these it reflects to the eye. 



Any substance or object which reflects none of the rays 

 which fall upon it, but absorbs all, appears black ; no rays 



