244 LAWS OF REFLECTION AND REFRACTION. 



BEFLBOTION FBOM A OONOAVK BCBFAOE. 



mirror, every line drawn from it to the mirror will be per- 

 pendicular to the surface at the point where it meets the 

 surface. Of course, rays coming from any point to the 

 mirror outside those lines will be reflected inside them, as 

 is seen in the upper ray from the candle B, which, after re- 

 flection, must go to the point b, making the angle of reflec- 

 tion equal to the angle of incidence. If rays, instead of 

 coming from a near object like B, come from a more dis- 

 tant one, the angles of incidence would be greater ; and if 

 they came from a distance so great as to make them sensi- 

 bly parallel as from the sun, for example then the lines 

 of incidence would be farther from the perpendicular on 

 the outside, and those of reflection would be farther on the 

 inside, so that the rays would meet in a point nearer the 

 glass, as at F, which is called the focus of parallel rays. 



This example shows clearly the general principle on 

 which all the calculations in respect to the effects pro- 

 duced by reflection are founded. Every thing depends 

 upon the position of the perpendicular in relation to the 

 incident ray, or, in other words, the angle at which the 

 incident ray comes to that part of the surface by which it 

 is to be reflected. Of course, as the directions of the com- 

 ing rays and the forms of the surfaces may be infinitely 

 raried, the special effects resulting are infinitely varied 

 too ; but this one simple principle governs them all. 



