376 TltE NATURE OF LIGHI. 



ECTION II. 



Si 



REFLECTION OF LIGHT. 



Note. The heliostat, or porte-lumiere, is composed of one or 

 more mirrors, by means of which a beam of light may be thrown 

 in any desired direction. The instrument may be had of apparatus 

 manufacturers at prices ranging from $12 upward. Directions for 

 making one may be found in Mayer & Barnard's little book on 

 " Light," published by D. Appleton & Co. It is very desirable that 

 the instrument be secured in some way. 



59 O. Reflection. If a sunbeam enter a darkened 

 room by a hole in the shutter, as at A, and fall upon a 



FIG. 278. 



polished plane surface, as at B, it will be continued in a 

 different direction, as toward C. AB is called the incident 

 beam and BC the reflected beam ( 97). The incident 

 and the reflected beams are in the same medium, the air. 

 A change in the direction of light without a change 

 in its medium is called reflection of light. 



591. Laws of Reflection. The reflection of light 



