308 OUR PHYSICAL WORLD 



When, during a shower, the sun is shining and is fairly near 

 the horizon, we may see a rainbow or, if in a balloon or on a 

 mountain peak, a rain circle. The light entering the raindrops 

 is refracted and dispersed, then totally reflected and further 

 refracted and dispersed as it leaves the drop. In the accompany- 

 ing figure (155) two of the raindrops are shown enlarged, so the 

 course of the light can be traced. The entering light is a heavy 

 line; the red light a light solid line, the violet light a dotted line; 

 the intermediate colors are omitted. The color perceived is 



FIG. 155. Diagram showing formation of the rainbow. Drops of water 

 represented by the small circles are in such position that beams of light entering 

 them are refracted and totally reflected so as to send to the eye red (solid line) 

 and violet (dotted line) rays. The eye projects these against the sky in a primary 

 bow and a dim outer secondary bow. Many thousands of drops are needed in 

 similar position to complete the bow. 



referred back along the line of the light entering the eye, and so 

 is seen against the sky or clouds. The color band is a bow 

 (or circle) because the observer is the center of curved rows of 

 such drops that can refract and reflect the light to his eye. 



If you fill a small spherical flask with water and set it on a 

 support near a window in a darkened room so that a beam of 

 sunlight entering through a small aperture in the curtain or 

 shutter will strike it, a circular rainbow will appear on the shutter. 

 This will be more evident if a sheet of white paper encircles the 

 opening in the shutter. 



