PHYSICAL FORCES 



105 



transparent medium is in part reflected, while the main 

 part which traverses it becomes refracted on the way. 

 It is this refraction of the rays of light which pass to 

 the eye from all the parts of a stick partly immersed in 

 water, which causes the stick to appear bent at the 

 point where it enters the liquid, and also causes any 

 solid object placed on the bottom of an empty vessel to 

 appear to change its place when the vessel has water 

 poured into it. 



This is due to the fact that such rays of light do not 



FIG. 21. 



proceed in a straight line to the eye from the object 

 looked at, but are deviated, bent or refracted, from the 

 point where they impinge upon the surface of the second 

 medium, as in passing from the water to the air. Thus 

 it is that refraction may enable us to " look round a 

 corner," because a ray of light proceeding from out 

 the water is bent, by refraction, so as to be more nearly 

 horizontal to the water's surface. 



Let E (Fig. 21) be the position of the observer's eye, C 

 that of a coin lying on the bottom of a vessel V, and the 



