428 REFLECTION OF LIGHT. 



that is, frorn 10 to 10 degrees. The division in the 

 middle is marked 0, the two on each side next to it are 

 marked 10, the next 20, and so on as far as 90. Begin- 

 ning with 0, there are apertures from 10 to 10. 



FIG. 243 (an. proj. real size). 



Opposite to the aperture at , in the flat side of the 

 vessel, is a small mirror, s, which is so adjusted that 

 on looking through the aperture opposite to it the re- 

 flected image of the aperture is seen exactly in the 

 middle of the mirror, which is only the case when the 

 straight line drawn from the aperture to the mirror is 

 perpendicular to the latter. 



If the eye is applied to the aperture at the division 

 10, the division 10 on the other side of will be seen 

 in the mirror ; if the mirror is observed through the 

 aperture at 20, the opposite division, 20, will appear 

 reflected, and so on. At whatever angle the light is 

 incident upon one side, it is reflected at the same angle 

 on the other side. 



This experiment on the law of reflection is still more 

 striking if performed in a dark room. If instead of the 

 eye the flame of a candle is placed pretty close to one 

 of the apertures, light passes through it, and the por- 

 tion which is incident upon the mirror is reflected in 

 such a manner as to illuminate the corresponding line 



