THE BOUNCING BALL. 



87 



that which was occupied in its descent ; for this it must 

 have if it is to rise at the same angle and attain to the 

 same height. 



There is the same tendency, substantially, when the ball 

 is thrown against a perpendicular wall, though in this case 

 the eftect is modified to a greater extent by the weight of 

 the ball. 



In the case of the reflection of liglit, the effect has noth- 

 ing to interfere with it, and the result is, that universally 

 the angle at which the light comes to the reflecting sur- 

 face on one side is the same as that at which it leaves it 

 on the other, or, as it is expressed scientifically, 



The angle of incidence is equal to the angle of reflection. 



This is one of the fundamental laws of optics. 



The principle is made plain by the engraving, where C 



ANGLES OF INCIDENCE AND REFLECTION. 



