456 



REFRACTION OF LIGHT. 



tion takes place is the /refracting surface/ and each of 

 the two substances is termed in reference to. this pheno- 

 menon c a refracting medium/ 



A round basin may be used instead of a square vessel for showing 

 the refraction of light which passes from air into water. The 

 boundary of the shadow is, however, in that case not a straight 

 line, but a curve, and the equality of the effect of refraction upon 

 the various rays which reach the edge of the vessel cannot be so well 

 observed. 



If a small heavy body, for example a coin, be placed 

 in an empty opaque bowl and the observer retires to such 

 a distance that the coin is just hidden from him by the 

 edge of the bowl, the coin comes into view again when 

 the vessel is filled with water, while the eye of the observer 

 retains its position unaltered; in fact, the whole bottom 

 of the vessel will seem to be lifted up, and the vessel will 

 appear shallower than it really is. The reason of this 

 is that light which passes from water into air is re- 

 fracted in a direction which is the reverse of that in 

 which light is refracted when passing from air into 

 water. The ray of light a b, fig. 258, which proceeds 



FIG. 258 (I real size). 



from the body, would take the direction b c if the vessel 

 were empty ; but on leaving the surface b d of the 

 water, it takes in consequence of refraction the direc- 



