232 



GENERAL SCIENCE 



Length of Light Waves 



Violet. . .',. .000397mm. Yellow. . . . .000589mm. 

 Indigo 000430 mm. Orange .... .000656 mm. 



Blue .... .000480 mm. 

 Green . .000527 mm. 



Red . .000689 mm. 



In the solar spectrum we notice that the bending in- 

 creases as the wave length decreases, the bending being 

 greater for the. violet light. The reason for the bending 

 of a ray as it strikes a transparent medium obliquely is 

 that its speed is changed, and the greater the change in 

 speed the greater the bending. Therefore, since the vio- 

 let light was bent more than the red light, the speed of 

 violet light in glass must be less than that of red. 



Red light waves are the longest and have the least 

 frequency of light waves producing visible rays. When 

 a piece of iron is heated to incandescence, it first gives off 

 red light. As the heating continues the activity of the 

 molecules and .electrons increases, producing shorter 



light waves and conse- 

 quently a change in color 

 to almost a pure white. 

 The rainbow is a solar 



FIG. 21 1 . An Artificial Rainbow. 



spectrum on a large scale. 

 Rainbows are caused by 

 the dispersion of sunlight 

 by drops of rain. They 

 may be seen only in the 

 morning and late after- 

 noon, since the sun must not be higher than 42 from the 

 horizon. In order to see a rainbow it is necessary to look 

 at falling raindrops upon which the sun is shining from 

 a position behind you. Miniature rainbows may be seen 

 in the spray from fountains or lawn sprinklers (Figure 211). 



