126 LIGHT 



The sun sends out waves of many different colors, 

 so many that we do not know the number. These 

 many-colored waves unite to form sunlight, which is 

 commonly said to be white light. Thus white light is 

 a mixture of many colors. 



147. The Spectrum. When light waves are refracted, 

 those that have the faster vibration rate are bent more 

 than those having the slower rate. Thus if a beam 

 of light ac (Fig. 99), containing three colors, red, 

 green, and violet, is refracted by a glass prism, the 



violet waves will be 

 bent most, the green 

 next, and the red least 

 ( 145). In this way 

 g the single beam ac 

 is split up, its three 

 n colors of waves are 

 separated, and each 



falls on a different spot on the screen mn. The appear- 

 ance of the separated colors on mn is called a spectrum. 



Experiment 97. Hold a glass prism (a cut-glass pendant or 

 stopper) so as to refract sunlight. A spectrum will be formed, 

 which may be seen somewhere about the room. Turn the prism 

 till the spectrum falls upon a wall or any surface where it may 

 be easily seen. This is the spectrum of white light (sunlight). 

 How many colors can you count? Name them in order. Does 

 each stop sharply, or gradually shade into those next to it ? 



The spectrum of white light shows seven distinct 

 shades; these are called the prismatic colors. In order, 

 they are red, orange, yellow, green, greenish blue, blue, 



