LIGHT. 97 



REFRACTION, 

 i. OF GLASS. 



Fig. 72. 



Project any object that is three or four inches long, 

 a lead pencil or an arrow cut out of paper. A single 

 lens is all that is needed. Then hold in front of the 

 object a piece of glass three or four inches long, 

 half an inch broad, and the thicker the better. If the 

 glass is held exactly perpendicular to the beam of light 

 no refraction will be observed ; but turn one end of it 

 towards the opening, and at once the picture upon the 

 screen will appear as if a piece of the object had been 

 cut out and was held to one side of it. The thicker 

 the glass is the greater will be the displacement ; but a 

 piece that is an eighth of an inch will quite likely make 

 as much difference as the thickness of the object pro- 

 jected. 



Two pieces of glass may be put together and held as 

 before, or turned in various directions with reference 

 to each other and the object. 



2 OF WATER. 



A hand mirror held at r will reflect the light down- 

 ward into the chemical tank (Fig. 73), which should be 

 filled with water in which a little finely powdered resin 



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