REFLECTION OF LIGHT. 



REFLECTION OF LIGHT. 



THE physical theories by which the phenomena connected with the propa- 

 gation of light are explained, have been given with some details on another 

 occasion. We shall now notice some of the more simple and elementary laws 

 of optics, which must stand undisturbed, whatever theory of light may be adopted. 



Whether light consists of undulations, or of corpuscles of matter, sui generis, 

 it is invariably propagated in straight lines so long as it passes through the 

 same medium ; the straight line along which the light holds its course is called 

 a ray of light, and any collection of such lines of definite thickness is called a 

 pencil of light. 



If the rays composing the pencil be parallel to each other, the pencil is 

 called a parallel pencil ; if the rays intersect each other at a point, the pencil 

 is said to diverge from or converge to that point according to the direction in 

 which the light is conceived to move, and the pencil is accordingly called a 

 converging or diverging pencil. 



If rays of light, after passing in straight lines through any uniform medium, en- 

 counter the boundary or surface of another medium of a different kind, they will 

 either turn back and take other directions in the medium from which they came, 

 or they will enter the new medium, and will in general take new directions in 

 it. In the former case the second medium is said to be opaque, and the rays 

 are said to be reflected from its surface ; in the latter case it is said to be 

 transparent, and the rays are sakjl to be refracted by it. 



Reflection and refraction are then two very important effects to which light 

 is subject, and it will be both interesting and profitable briefly to notice the lead- 

 ing principles that govern these phenomena. 



REFLECTION OF LIGHT. 



The surfaces of opaque bodies reflect the light incident upon them in 

 various ways, and produce a corresponding variety of effects thereby on the 

 sense of sight. 



