CHAPTER XXIII 

 COLOR 



134. Composition of Light. Light, as it ordinarily comes to 

 us from the sun, is called white light, but if a beam of this light 

 be directed through a glass prism, we discover that, instead 

 of white light, we have a band of several different colors called 

 the primary or prismatic colors, with red at one end, violet at 

 the other, and orange, yellow, green, blue, and indigo between. 



"FiG. 58. Formation of the spectrum by a prism. (Tower, Smith 

 and Turton.) 



The colors are due to differences in the speed with which the 

 rays of light vibrate and the resultant effects of these rays on 

 the eye. Those which give us the sensation of red, vibrate 

 392,000,000,000,000 times a second, while the violet rays 

 vibrate more than twice as fast. Passing light through a prism 

 merely serves to sort out the different rays. If these are 

 brought to a focus by a lens, or are mixed in any other way, 



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