240 LAWS OF REFLECTION AND REFRACTION. 



CHAPTER XXVI. 



LAWS OF REFLECTION AND REFRACTION. 



WHEN a ray of light passes from the air through any 

 transparent medium which is denser than air, as glass or 

 water, for instance, if it enters and leaves the denser medi- 

 um at right angles to the surface, its course, it will be rec- 

 ollected, is not changed in its passage, but if it enters or 

 leaves at any oblique angle, it is turned somewhat from a 

 straight course both in entering and leaving. 



Now we have seen in the case of reflection that, inas- 

 much as the direction in which a ray is reflected depends 

 upon the angle at lohich it strikes the reflected surface, it fol- 

 lows that when the surface is curved, the different rays of 

 any pencil or beam will be reflected differently, because the 

 curvature of the surface makes the angle at which the ray 

 is reflected different from what it would be if the surface 

 was plane, and thus the condition of the rays in relation to 

 each other is very materially altered by such reflection. 

 Parallel rays may become convergent or divergent, and 

 divergent rays may become convergent or parallel. 



It is the same in respect to refraction. If the surface is 

 plane, so that all the rays entering it are subject to refrac- 

 tion under the same conditions, they are all bent in the 

 same manner; and if they at last enter the eve and form an 

 image, the image is not changed in any thing except in ap- 

 parent direction from which the rays forming it come to 

 the eye. 



This is what happens when we look at an object seen ob- 

 liquely under water; it seems raised somewhat, but is not 



