

THE BEASON WHY. 



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'Blessed be the Lord, who daily loadeth us with benefits, even the God of our 

 salvation." PSALM LXVIII. 



520. What is the line of reflection ? 



The line of reflection is the line in which the rays of light are 

 returned from the image formed in the glass to the eye of the 

 observer. 



Reflection & turning back. 



521. What is the angle of incidence? 



The angle of incidence is the angle which rays of light, falling on 

 a reflecting surface, make with a line perpendicular to that surface. 



.Reflecting Surface. 



Fig. 14. EXPLAINING THE LINES AND ANGLES OF INCIDENCE AKD 



OP KEFLECTION. 



522. What is the angle of reflection ? 



The angle of reflection is the angle which is formed by the 

 returning rays of light, and a line perpendicular to the reflecting 

 surface. It is always equivalent to the angle of incidence. 



Take a marble and roll it across the floor, so that it shall strike the wainscot 

 obliquely. Let A in the diagram represent the point from which the marble is 

 sent. The marble will not return to the hand, nor will it travel to the line B, 

 but will bound off, or be reflected, GO C. Now B is an imaginary line, perpen- 

 dicular to the reflecting surface; and it will be found that the path described 

 by the marble in rolling to the surface and rebounding from it, form, with the 

 li ne B, two angles that are equal. These represent the angles of incidence and 

 of reflection, and explain why the reflection of a person standing at A before a 

 mirror, would be seen by another person standing at C. This simple law iu 

 optics explains a great many interesting phenomena, and therefore it should be 

 clearly impressed upon the memory. 



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