378 GENERAL SCIENCE 



Light Obtained from Electric Lamps. Of electric lights there 

 are several kinds used in the household : the metalized carbon, called 

 the " Gem," the " Tungsten " lamp, usually known under the name 

 of " Mazda," and the ordinary carbon lamp. Fig. 262 will show 

 the comparison of the amount of light given by different lights 

 at the same cost. 



QUESTIONS 



1. What would be the effect if you were reading 8 feet from 

 a- lamp and you moved 24 feet away, the candle power of the 

 lamp being 32? 



2. What is the cheapest form of gas light to use? 



3. Why are mantles economical? 



4. What is the cheapest type of electric light to use? 



5. What causes an object to have color? 



6. Why is it impossible to match colors in artificial light? 



7. How are most of our colored pictures in magazines obtained? 



8. Why will a white table cloth on a mahogany table make a room 

 lighter? 



9. Why should rooms be well lighted? 



COLOR AND CHEMICAL ACTION OF LIGHT 



Color. No object has any color of its own but depends for its 

 color upon the light rays which are reflected by the material. There 

 are three sets of nerves in the retina of the eye; one sensitive to 

 red, another to green, and a third to blue light waves. When all 

 three of these nerves are stimulated equally, white is obtained. If 

 only the red nerves are stimulated, the person sees red; likewise 

 blue and green when the blue and green sets of nerves are stimu- 

 lated. If one nerve is stimulated more than another, there is 

 an uneven mixture of color sensation, and intermediate colors are 

 produced. 



The shade of these colors varies according to the amount of 

 stimulation. Black objects absorb all the light rays. White objects 

 reflect all light rays. If an object appears red, it means that all the 

 light rays have been absorbed except red. The same is true of other 



