LENSES 



355 



FIGURE 103 



stalks and will move faster, and thus the line of march will 

 swing in toward the edge of the corn field. It can easily be 

 seen that the bending of the line would be in the opposite 

 direction if the soldiers were 

 marching from the smooth field 

 into the corn field. If the com- 

 pany front were parallel to the 

 edge of the corn field, then the 

 men would reach the open field 

 at the same time and there 

 would be no swinging of the line. 



The above illustration roughly explains what happens 

 when light passes from one medium to another. Refrac- 

 tion is the name given to this bending of light in passing 

 through different media or through a medium of changing 

 density. Twilight, mirage, the flattening of the sun's 

 disk at the horizon, and other appearances, we shall find 

 later, are due to this property of light. 



Lenses. The bending of light in passing from one 

 medium to another has been turned to great advantage in 



the use of lenses. In the 

 making of lenses, trans- 

 parent substances are so 

 shaped that when the rays 

 of light strike them, they 

 are bent into any desired 

 direction. Experiment 105 



shows that the rays may be brought nearer together 

 (converged or focused) or spread farther apart (diverged). 

 If the illustration of the line of march of the soldiers is 

 kept in mind, it will be seen that the rays must always 



