THE PATH OF LIGHT 



245 



ray also makes an angle of 32 with the perpendicular. The 

 ray (AC, Fig. 113) which falls upon the mirror is called the 

 incident ray, and the angle which the incident ray (AC) makes 

 with the perpendicular 

 (BC) to the mirror, at the 

 point where the ray strikes 

 the mirror, is called the 

 angle of incidence. The 

 angle formed by the re- 

 flected ray (CD) and this 

 same perpendicular is 

 called the angle of reflec- 

 tion. Observation and ex- 



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periment have taught US FIG. 114. A bouncing ball illustrates the 

 that light is always re- law of reflection. 



fleeted in such a way that the angle of reflection equals the 

 angle of incidence. Light is not the only illustration we have 

 of the law of reflection. Every child who bounces a ball 

 makes use of this law, but he uses it unconsciously. If 



an elastic ball is thrown 

 perpendicularly against the 

 floor, it returns to the 

 sender; if it is thrown 

 against the floor at an angle 

 (Fig. 114), it rebounds in 



FIG. 115. The image is a duplicate of the 

 object, but appears to be behind the 

 mirror. 



the opposite direction, but 

 always in such a way that 

 the angle of reflection equals 

 the angle of incidence. 

 Why the image seems to be behind the mirror. If a candle 

 is placed in front of a mirror, ED in Figure 115, one of the rays 

 of light which leave the candle will fall upon the mirror as 

 AB and will be reflected as BC (in such a way that the angle 



