LIGHT 



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part of the day, when the bright sun appears before the 

 cloud has disappeared. The reason that a rainbow is 

 not seen in the morning is because the clouds as a rule 

 travel from west to east, and the front of the cloud usually 

 hides the sun before any rain falls. After the cloud is 

 past, the sun is not in the right position to shine on the 

 falling drops. So rainbows are seen by looking east just 

 after a shower, and usually in summer, because the 

 winter clouds do not pass away quickly enough for the 

 sun to shine on the falling rain. 



To understand how a rainbow is made, let us examine 

 the illustration. MN is a large cardboard with an opening 

 at O for the light of the sun to enter the room. The 

 light passes into the two- 

 inch spherical flask at A, 

 and is refracted as it enters, 

 just as when light passes 

 through a prism. It goes 

 through the water to the 

 other side of the flask at B, 

 from which it is reflected to 

 C. As it comes out of the 



flask at C it is refracted again, thus spreading the red 

 and violet rays farther apart. From C the light goes to 

 the cardboard, with the violet and red at the positions 

 indicated and the other colors of the spectrum between 

 the red and violet. Since violet is refracted most, it will 

 be nearest the center of the circle. Only one ray of light 

 is represented in the drawing, but the rainbow spectrum 

 is a complete circle around the hole 0. 



The natural rainbow seen after a rain is due to the 

 refraction of the sunlight as it passes into and out of a 

 drop of falling water and the reflection of this light from 



PRODUCING AN ARTIFICIAL RAINBOW 



