272 COLOR 



or separated into all the colors which it contains, and a band of 

 colors produced in this way is called a spectrum. If we examine 

 such a spectrum, we find the following colors in order, each 

 color imperceptibly fading into the next: violet, blue, green, 

 yellow, orange, red. 



Color. If a piece of red glass is held in the spectrum, all 

 the colors on the wall disappear except the red, and instead 

 of a beautiful spectrum of all colors there is seen the red color 

 alone. The red glass does not allow the passage through it of 

 any light except red light; all other colors are absorbed by the 

 red glass and do not reach the eye. Only 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 light is seen and all the other colors disappear. 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 the various rays with the exception of the blue 

 ones, and the red glass will not allow these blue rays to pass 

 through it. No light passes to the eye. 



An emerald looks green because it freely transmits green, 

 but absorbs the other 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 deli- 

 cacy of the pigments used. 



