THE CROOKED COURSES OF LIGHT. 



33 



The principle of reflection is illustrated in Fig. 1, in which a beam" 

 of the sun's rays enters through the shutter of a dark room, strikes 

 upon a polished plane surface, and is reflected across the room in an 

 opposite direction. The entering beam, A B^ is called the incident 

 ray. The vertical line, B 7>, is termed the normal^ and the beam B (7, 



Illustration of the Reflection of Light. 



the reflected ray. The angle A D B^ contained between the incident 

 ray and the normal, is termed the angle of incidence ; and the angle 

 C B JD^ contained between the corresponding reflected ray and the 

 normal, is called the angle of reflection. The reflection of light by pol- 

 ished surfaces, as in this case, is governed by two laws: 1. The inci- 

 dent ray, the normal, and the reflected ray, are always in the same 

 plane; and, 2. The angle of incidence is always equal to the angle 

 of reflection. 



Fig. 2. 



Image of a Candle in a Looking-Glass. 



This is an example of what is known as regular reflection, but 

 there is another kind of reflection in virtue of which bodies, when illu- 



