i68 



Common Science 



FIG. 94. A mercury-vapor lamp. 



lights are long, inclined tubes which glow with a greenish- 

 violet light. No matter how good the color of a person 

 is in ordinary light, in that light it is ghastly. 



Go into the kitchen tonight, light a burner of the gas 

 stove, turn out the light and sprinkle salt on the blue 

 gas flame. The flame will leap up, yellow. Look at 

 your hands, at some one's lips, at a piece of red cloth, 

 in this light. Does anything look red ? 



The reason why nothing looks pink or red in these 

 two kinds of light is this : The light given by glowing 

 salt vapor or mercury vapor has no red in it; if you 

 tried to make a " rainbow " from it with a prism, you 

 would find no red or orange color in it. A thing looks 

 red when it absorbs all the parts of the light that are 

 not red and reflects the red light to your eyes. If there 



