172 Common Science 



Copper vapor always gives this greenish-blue light 

 when it is heated. The photographer's mercury-vapor 

 light gave a greenish-violet glow. When you burn salt 

 or soda in a gas flame, you remember that you get a clear 

 yellow light. By breaking up these lights, somewhat 

 as you broke up the sunlight with the prism, chemists 

 and astronomers can tell what kind of gas is glowing. 

 The instrument they use to break up the light into its 

 different colors is called a spectroscope, and the band of 

 colors formed is called the spectrum. With the spectro- 

 scope they examine the light that comes from the sun 

 and stars and by the colors of the spectra they can tell 

 what these far-distant bodies are made of. 



Application 39. If you were going to the tropics, would 

 it be better to wear outside clothes that were white or black ? 



Application 40. A dancer was to dance in a spotlight on 

 the stage. The light was to change colors constantly. She 

 wanted her robe to reflect each color that was thrown on it. 

 Should she have worn a robe of red, yellow, white, green, or 

 blue? 



Application 41. If you looked through a red glass at a 

 purple flower (purple is red mixed with blue), would the 

 flower look red, blue, purple, black, or white? 



Inference Exercise 

 Explain the following : 



241. Mercury is separated from its ore by heating the ore so 



strongly that the mercury rises from it as a vapor. 



242. Hothouses are built of glass. 



243. A " rainbow " is sometimes seen in the spray of a garden 



hose. 



244. Your feet become hot when your shoes are being polished. 



245. Doors into offices usually have windows of ground glass or 



frosted glass. 



