REFRACTION OF LIGHT. 



313 



Fig. 250. 



Fig. 251. 



Wliea liglit passes obliquely out of a denser into a rarer 

 medium, it passes through the rarer medium in a more 

 oblique direction, and further from a perpendicular to the 

 surface of the denser medium. 



Thus, in Fig. 250, suppose n m to represent the 

 surface of water, and S a ray of hght striking 

 upon its surface. When the ray S enters tho 

 water, it will no longer pursue a straight course, 

 but will be refracted, or bent toward the perpen- 

 dicular line, A B, in the direction S 0. The denser 

 the water or other fluid may be, the more the ray 

 S H will be refracted, or turned toward A B. 

 If, on the contrary, a ray of light, H 0, passes from 

 the water into the air, its direction after leaving the water will be further from 

 the perpendicular A 0, in the direction S. 



The effects of the refraction of 

 light may be illustrated by the fol- 

 lowing simple experimenc : — Let a 

 coin or any other object be placed 

 at the bottom of a bowl, as at m, 

 Fig. 251, in such a manner that the 

 eye at a can not perceive it, on ac- 

 count of the edge of the bowl which 

 intervenes and obstructs tlie rays of 

 light. If now an attendant care- 

 fully pours water into the vessel, the 

 coin rises into view, just as if the bottom of the basin had been elevated 

 above its real level. This is owing to a refraction by the water of the rays 

 of light proceeding from the coin, whicli are tliereby caused to pass to tho 

 eye in the direction i i. The image of the coin, therefore, appears at n, in tho 

 direction of these rays, instead of at m, its true position. 



A straight stick, partly immersed in water, appears to be broken or bent 



at the point of immereion. This is owing to the fact that the rays of light 



proceeding from the part of the stick contained in the water are refracted, or 



Fig. 252. caused to deviate from a straight line as they pass from the 



■n-ater into the air ; consequently that portion of the stick 



immersed in the water will appear to be lifted up, or to 



be bent in such a manner aa to form an angle -with the 



part out of the water. 



The bent appearance of the stick in water is represented 

 in Fig. 252. For the same reason, a spoon in a glass of 

 water, or an oar partially immersed in water, always ap- 

 pears bent. 



On account of this bending of light from objects under water, a person who 

 endeavors to strike a fish with a spear, must, unless directly above the fish, 



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