REFRACTION 



the dangerous typhoid germs are present. The future of 

 medicine will depend somewhat upon the additional secrets 

 which man is able to force from nature through the use 

 of powerful lenses, because as lenses have, in the past, 

 been the means of revealing disease germs, so in the fu- 

 ture more powerful lenses may serve to bring to light 

 germs yet unknown. How refraction accomplishes these 

 results will be explained in the following Sections. 



no. The Window Pane. We have seen that light is bent 

 when it passes from one medium to another of different 

 density, and that objects viewed by refracted light do not ap- 

 pear in their proper positions. 



When a ray of light passes through a piece of plane glass, 

 such as a window pane (Fig. 67), it is refracted at the point B 



toward the perpendicular, and 

 continues its course through 

 the glass in the new direc- 

 tion BC. On emerging from 

 the glass, the light is re- 

 fracted away from the perpen- 

 dicular and takes the direc- 

 tion CD, which is clearly par- 

 allel to its original direction. 

 Hence, when we view objects 

 through the window, we see 



pane seem to be in their natural them slightly displaced in 



position, but otherwise un- 

 changed. The deviation or displacement caused by glass as 

 thin as window panes is too slight to be noticed, and we are 

 not conscious that objects are out of position. 



in. Chandelier Crystals and Prisms. When a ray of light 

 passes through plane glass, like a window pane, it is shifted 

 somewhat, but its direction does not change ; that is, the 



FIG. 67. Objects looked at through a 

 windo 

 place. 



