76 



PRACTICAL LESSONS IN SCIENCE. 



parent substances. This is shown by the bending or breaking 

 of a ray of light as it passes from one medium into another of 

 different density, if the ray is oblique to the surface separating 

 the two media. Thrust a pencil into the water so that it is per- 

 pendicular to the surface of the water and there is no apparent 

 change in the shape of the pencil, but if it be made oblique to the 

 surface of the water it appears to be bent or broken at the sur- 

 face, and the immersed portion seems elevated. Again, place a coin 

 on the bottom of an opaque dish as at B (Fig. 10), then standing 

 so that the coin is just hid from sight by the side of thedish,have 

 water poured slowly into the dish and the coin will rise into view 



as the dish fills with 

 water. The difficulty 

 of putting a stick on a 

 given object in a body 

 of water is a familiar 

 illustration of the 

 same principle. Now, if 

 we remember that ob- 

 jects are seen by light 

 reflected from them, 

 we know that a ray of 

 light from the coin or 

 pencil point, is bent at the surface of the water at C toward A, 

 instead of going on to E, so that the ray appears to come from 

 D, and the coin seems to have been lifted from B to D, the pencil 

 appearing to be shorter and the water shallower than it is in 

 reality. If one looks at a pencil so that one part is seen through 

 glass oblique to the surface, and the other part through air, the 

 pencil appears broken at the surface of the glass, on account of 

 refraction of light. 



The laws of refraction are that a ray of light, in passing from 

 a rarer into a denser medium, is bent toward the perpendicular 

 at the point of incidence, while in passing from a denser into a 

 rarer medium it is bent from the perpendicular at the point 

 of incidence. (See Fig. 10.) The angle ACF is the angle of 



FIG 10 



