OPTICS. '^61 



OF REFLECTION. 



When the rays of light strike upon an opaque 

 body, apart of them is reflected, or made to rebound 

 in the same manner as a boy's marble does when 

 thrown upon a stone pavement; but the whole of 

 the rays is not reflected, a certain part being re- 

 tained or absorbed by the opaque body. 



It is a fundamental law in the reflection of the 

 rays of light, as well as of all other elastic bodies, 

 that the angle at which they rebound or are reflected 

 from the surface of the reflecting body, is the 

 same as that with which they impinge upon it. 



Thus let F C (Plate 12. fig. 1.) be a ray of light 

 falling perpendicularly upon the surface L G; it 

 will be reflected back again in the same direction 

 C F. But if a ray B C falls upon the surface 

 obliquely, then the angle B C L will be called the 

 angle of incidence' ; and when it has arrived at the 

 surface L G, it will be reflected in the direction 

 C E, making E C G, called the angle of reflection, 

 equal to B C L. This is stated shortly by saying, 

 that the angles of incidence and reflection are 

 equal. 



It is supposed that in the reflection of light, it 

 does not actually come into contact with the sur- 

 face of the body that reflects it, but that this effect 

 is occasioned by some power that acts at a small 

 distance from the surfaces of bodies. For, it is 

 argued, that as the smoothest and best polished 

 surfaces are so only in appearance, being in 

 reality rugged and uneven, (polishing being nothing 

 but the covering over with fine scratches, and 

 breaking off the protuberances of bodies,) if light 

 was reflected by actually striking on the solid 



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