120 APPLIED SCIENCE 



looks red because it selects from white light mainly red for 

 reflection. 



125. Theory of Color. Sunlight is called white light, and 

 is, as just noted, composed of all the colors of the rainbow. 

 When sunlight falls upon a body, a part of the light is ab- 

 sorbed by the body and converted into heat. The rest of 

 the light is reflected to the eye and renders the body visible. 

 If the body reflects all the colors of the rainbow equally, 

 then the body is white. If the molecules of the body absorb 

 certain compound colors of sunlight, then the reflected light 

 is deprived of those particular colors. To illustrate: If blue 

 is absorbed, the light reflected will be deprived of this primary 

 color and the active remaining color which is red will pre- 

 dominate. Thus, the body will appear red. 



This theory of light has been used to advantage in protect- 

 ing the eyes of the workmen engaged in electric and oxy- 

 acetylene welding. When metals are heated to a very high 

 temperature, the eyes of the workman may be damaged by 

 the repeated flashes of brilliant light from the glowing metals. 

 Very careful experiments show that certain rays in large 

 amounts, such as the ultra-violet rays and the infra-red 

 rays, are harmful. Such rays are present in the working of 

 molten iron or steel, or any incandescent material, where 

 the temperature is 2000 F. or more. Special colored 

 glasses or lenses will neutralize or cut out these dangerous 

 rays. 



126. Table of Colored Lenses. The following table indi- 

 cates the kind of colored lenses which should be used to nullify 

 or prevent any injury to the eyes from the industrial pro- 

 cesses tabulated below. 



