CHAPTER II. 



REFLEXION AND REFRACTION. 



(22) WHEN light meets the surface of a new medium, a 

 portion of it is always turned back, or reflected. 



The reflection of light is twofold. Thus, when a beam of 

 solar light is admitted into a darkened chamber through an 

 aperture in the window, and is allowed to fall upon a metallic 

 mirror, a reflected beam is seen pursuing a determinate direc- 

 tion, after leaving the mirror ; and if the eye be placed in this 

 direction, it will perceive a brilliant image of the sun. This 

 beam is said to be regularly reflected, and its intensity increases 

 with the polish of the mirror. But it is observed also, that 

 in whatever part of the room the eye is placed, it can always 

 distinguish the portion of the mirror which reflects the light ; 

 some of the rays, consequently, are reflected in all directions. 

 This portion of the light is said to be irregularly reflected, and 

 its intensity decreases with the polish of the mirror. 



Irregular reflexion is due, mainly, to the inequalities of the 

 reflecting surface, which is composed of an indefinite number 

 of reflecting surfaces in various positions, and which, there- 

 fore, reflect the light in various directions. 



(23) The angles of incidence and reflexion or the angles 

 which the incident and reflected rays make with the perpen- 

 dicular to the reflecting surface at the point of incidence 

 are in the same plane, and are equal. This law is universally 

 true, whatever be the nature of the light itself, or that of the 

 body which reflects it. 



