378 REFLECTION OF LIGHT. 



(c.) Place two of the screens and the three extra blocks men- 

 tioned in 584 in position, as shown in Fig. 280. At the middle 

 of the middle block place a bit of window glass, painted on the 

 under side with black varnish. On the blocks that carry the screens 

 place bits of glass, n and o, of the same thickness as the black mir- 

 ror on the middle block. Place a candle flame near the hole in one 

 of the screens, as shown in the figure. Light from the candle will 

 pass through A, be reflected at m, and pass through B. Place the 

 eye in such a position that the spot of light in the mirror may 

 be seen through B. Mark the exact spot in the mirror with a 

 needle held in place by a bit of wax. Place a piece of stiff writing 

 paper upright upon m and n, mark the position of B and of m, 

 and draw on the paper a straight line joining these two points. 

 The angle between this line and tho lower edge of the paper 

 coincides with the angle Bmn. Reverse the paper, placing it upon 



FIG. 280. 



m and o. It will be found that the same angle coincides with 

 Amo. Amo and Bmn being thus equal, the angle of incidence 

 equals the angle of reflection. 



592. Diffused Light. Light falling upon an 

 opaque body is generally divided into three parts : the 

 first is regularly reflected in obedience to the laws above ; 

 the second is irregularly reflected or diffused ; the third is 

 absorbed. The irregular reflection is due to the fact that 

 the bodies are not perfectly smooth, but present little pro- 

 tuberances that scatter the light in all directions, and thus 

 render them visible from any position. Light regularly 

 reflected gives an image of the body from which it came 

 before reflection : light irregularly reflected gives an image 



