REFRACTION OF LIGHT. 



455 



biscuit-box, is placed upon the table at such a distance 

 from a lamp or candle that the bottom of the vessel 

 may be just in the shadow of one of the sides, as 

 shown in fig. 257 A. The front of the vessel is left 

 out in the figure in order to exhibit the interior, 

 which in reality could only be seen by looking into the 

 vessel from above. If the vessel is now filled with 

 water, the bottom of the vessel, as shown in fig. 2575, 

 is no longer entirely in the shadow; the rays of light 



FIG. 257 (an. 



which strike on the surface of the water proceed in 

 the liquid in a more slanting direction than that in 

 which they were propagated in the air. This change 

 in the direction of rays of light which pass from 

 one transparent substance (air) into another (water) is 

 called refraction of light; the surface where the refrac- 



