* 



Chap, xxiv.] THE REFLECTION OF LIGHT. 301 



the image ; because the more limited the extent of 

 surface illuminated by the separate rays, the less ten- 

 dency there is to overlapping. 



The intensity of light varies inversely as the 

 square of the distance from the source of light. 



Fig. 127. Reflection of Light. 



REFLECTION OF LIGHT. 



"When a ray of light falls upon a polished surface, 

 it is reflected in a definite direction. Let CD (Fig. 127) 

 be a polished surface on which a ray of light AB 

 falls, the ray will be re- 

 flected from the surface 

 in the direction BE. AB 

 is called the incident, and 

 BE the reflected ray. Let 

 a line FB be dropped per- 

 pendicular to the surface ; 

 this line is called the 

 normal to the surface. The point B where the ray 

 falls is the point of incidence, and the angle ABF 

 (the angle a), made by the incident ray and the 

 normal, is the angle of incidence, while the angle 

 EBF (angle b), made by the reflected ray and the 

 normal, is the angle of reflection. Now it is found 

 that these two angles are equal to one another and 

 are in the same plane. Thus the two laws of re- 

 flection of light are : (1) the angle of incidence is equal 

 to the angle of re/lection ; and (2) the incident and re- 

 flected rays are in the same plane. The application of 

 these rules explains the formation of images of ob- 

 jects by mirrors. 



Mirrors may be plane or curved. 



Plane mirror*. Let PP' be a plane mirror 

 (Fig. 128) ; and suppose AB to be an arrow placed in 

 front of it. Consider rays of light falling from the 

 point A of the arrow, and meeting the mirror ; 



